Programmer 7500/MAX_PROGRAMMERS.iso/WIN_NT/KMGLOS.ZIP/GLOS.TTY

Text File | 1993-01-29 | 117.4 KB | 3,499 lines

             Glossary of Terms and Acronyms             Glossary of Terms and Acronyms

             access violation             access violation
                An attempt to carry out a memory operation that is not
                allowed by the underlying page protection. See also probe
                and SEH.
                   There are four basic kinds of actions that can cause
                   access violations:
                   1   Attempting an invalid operation, such as writing to a
                       read-only buffer.
                   2   Attempting to access memory beyond the limit of the
                       current program's address space (a.k.a. "length
                       violation").
                   3   Attempting to access a page to which the system
                       forbids access. For example, code is not allowed to
                       run in the low-order 64K of the NT user-mode address
                       space in order to simplify the detection of NULL
                       pointer references.
                   4   Attempting to access a page that is currently
                       resident but dedicated to the use of an executive
                       component. For example, user-mode code is not allowed
                       access a page that the Kernel is using.
                   Note that this term pertains to memory operations. It has
                   nothing to do with the Security Manager's checking of
                   user-mode access rights to objects. See security
                   violation, ACE, and ACL.

             ACE             ACE
                (1) Access control entry
                   An ACE is an individual entry in an ACL. An ACE contains
                   an SID and describes the access rights that a particular
                   user or group of users has to a system resource. The set
                   of all ACEs on the object are used to determine whether
                   an access request to the object is granted. See also
                   security descriptor.
                (2) Advanced computing environment
                   A consortium of hardware and software companies formed to
                   promote an open computing environment. NT is one of the
                   original ACE operating systems.

             access right             access right
                A permission granted to a process to manipulate a particular
                object in a particular way (by calling a service). Different
                NT object types support different access rights, which are
                stored in an object's ACL.
















        G-2      Kernel-mode Driver Design Guide        G-2      Kernel-mode Driver Design Guide


        ACL        ACL
           Access control list
              An ordered list of ACEs.

        adapter object        adapter object
           A kernel-mode-only object type, defined by the I/O Manager
           and supported by the HAL component. An adapter object
           represents a hardware bus adapter or DMA controller channel.
           Adapter objects "connect" different kinds of devices on the
           bus or DMA controller, each device (or kind of device) with
           its own driver.

        affinity        affinity
           A programmer-defined attribute of a process and/or thread on
           a multiprocessor platform:
           n  For a process, its affinity is the programmer-determined           n
              set of processors on which its threads are permitted to
              run.
           n  For a thread, its default affinity is identical to that           n
              of the process to which it belongs; otherwise, its
              affinity must be a proper subset of the process's.

        alert        alert
           A Boolean that provides a way to break into a thread's
           execution at a point where either of the following
           conditions is met:
           n  The thread is in an alertable wait state (as specified           n
              when the wait service was called).
           n  The thread polls the alerted flag.           n

        APC        APC
           Asynchronous procedure call
              An APC is a Kernel-defined control object representing a
              procedure that is called asynchronously. APCs are thread-
              context dependent; that is, they are queued to a
              particular thread for execution.
              There are three different kinds of APCs in NT:
              1   User APCs - These APCs are used by certain                  _________
                  asynchronous NT system services to allow users to
                  synchronize the execution of a thread with the
                  completion of an operation or the occurrence of an
                  event such as a timer's expiration. User APCs are, by
                  default, disabled. That is, they are queued to the
                  user's thread, but they are not executed except at
                  well-defined points in the user's program.
                  Specifically, they can only be executed when the user
                  has called a wait service and has enabled alerts to
















                            Glossary of Terms and Acronyms      G-3                                 Glossary of Terms and Acronyms      G-3


                       occur, or if the user has called the test-alert
                       service.





























































        G-4      Kernel-mode Driver Design Guide        G-4      Kernel-mode Driver Design Guide


              2   Kernel APCs - These APCs are normal kernel-mode APCs.                  ___________
                  They are much like a normal user APC except that they
                  are executable by default. That is, they are enabled
                  except when the thread is already executing a Kernel
                  APC.  (Note that a special Kernel APC always preempts
                  these.)
              3   Special Kernel APCs - These APCs cannot be blocked                  ___________________
                  except by running at a raised IRQL. They are executed
                  at APC_LEVEL IRQL (see IDT), in kernel mode. These
                  types of APCs are used by the system to force a
                  thread to execute a procedure in the thread's
                  context. An example of this is I/O completion:  the
                  I/O Manager needs to get back into the context of the
                  original requestor of the I/O operation so that it
                  can copy buffers, etc. In order to do this, the I/O
                  Manager must be able to access the virtual address
                  space of the thread/process, and the most efficient
                  way to complete the operation is to be in the calling
                  thread's context.

        ARC        ARC
           (1) The NT executive runs on top of ARC-compliant machines,
           including both RISC- and CISC-based platforms that supply
           the following components to the OS loader:
           n  In MIPS-based platforms, a set of machine firmware that           n
              supports bootstrap loading and execution as an
              "abstracted" set of ARC routines and ARC devices.
           n  In x86-based platforms, a hardware recognizer (Ntdetect)           n
              that finds devices necessary to bootstrap the system by
              querying the ROM BIOS and builds a hardware database that
              emulates the RISC-based ARC firmware.
           n  In both kinds of platforms, a HAL that interfaces between           n
              the hardware and NT.
           Later in the load process, the driver of the disk, CD-ROM,
           or floppy device from which the system booted creates an
           alias between the name of its device object and the
           corresponding ARC device name by calling IoAssignArcName.                                                    IoAssignArcName
           (2) Advanced RISC computing
              Refers to a RISC-based computer architecture standard,
              associated with the ACE consortium.

        associated IRP        associated IRP
           One of a set of IRPs, created by the highest-level driver in
           a chain of layered drivers, that specifies some part of an
           I/O request to be sent on to a lower-level driver. When all
           associated IRPs in the set have been processed, the highest-
           level driver completes the original request. See also IRP.
















                            Glossary of Terms and Acronyms      G-5                                 Glossary of Terms and Acronyms      G-5


             asynchronous I/O             asynchronous I/O
                A model for I/O in which the operations carried out to
                satisfy I/O requests do not necessarily occur in sequence.
                The application that originally made the request can
                continue executing (rather than waiting for its I/O to
                complete), the I/O Manager or a high-level driver can
                reorder I/O requests as they are received, and a low-level
                driver can start an I/O operation on a device before it has
                completed the preceding request, particularly in a
                multiprocessor machine.

             backing store             backing store
                A mass storage medium, such as a disk, that serves as backup
                "memory" for paging when physical memory becomes full. See
                also paging file.

             balance set             balance set
                The set of processes currently in the system, in particular,
                processes whose threads are eligible for execution. See also
                dispatch state and working set.
                   At any given moment, the balance set depends on the
                   availability of physical memory (pages) to back the
                   virtual address space associated with each active
                   process. If a physical memory shortage occurs, the NT
                   Memory Manager first trims the working set of each active
                   process to its minimum, then (if necessary) removes
                   processes from the balance set.

             based section             based section
                A section allocated at the same virtual address for each
                process that has a view of the section. See also section and
                view.

             BCB             BCB
                Buffer control block
                   An opaque Cache Manager structure, used to maintain state
                   as a file system pins and releases data (for example, its
                   volume structure) in the cache.

             big-endian             big-endian
                Refers to a memory architecture in which the byte layout is
                as follows:
                n  Byte N is the most significant (and, in conventional                n
                   layout diagrams, the "leftmost") byte of:
                   n   A word composed of bytes N and (N + 1).                   n
                   n   A double word composed of bytes N, (N + 1), (N + 2),                   n
                       and (N + 3).
















        G-6      Kernel-mode Driver Design Guide        G-6      Kernel-mode Driver Design Guide


              n   A K-byte memory entity composed of bytes N, (N +              n
                  1),...,(N + K - 1).
           n  The address of the preceding word, double word, or K-byte           n
              entity is its most significant byte, N.



























































                            Glossary of Terms and Acronyms      G-7                                 Glossary of Terms and Acronyms      G-7


                A MIPS machine can be configured for either big-endian or
                little-endian byte addressing. For a big-endian
                configuration, the most significant bit of a 16-bit short                                                                    short
                value is the "leftmost" bit at byte N, while the least
                significant bit is the "rightmost" bit of byte (N + 1). See
                also little-endian.
                   The terms "big-endian" and "little-endian" are derived
                   from Jonathan Swift's Gulliver's Travels.                                         __________________

             Cache Manager             Cache Manager
                An executive component that provides file caching support
                for NT file system drivers.

             CCB             CCB
                Context control block
                   An internal NT-defined file system structure, in which a
                   file system maintains per file object state for an open
                   instance of a file. See also FCB and DCB.

             CDB             CDB
                Command descriptor block
                   A structure, defined by the SCSI-II standard, used to
                   communicate requests to a target device on the SCSI bus.

             CDFS             CDFS
                CD-ROM file system

             CD-ROM             CD-ROM
                Compact disk, read-only memory

             chase             chase
                To follow a linked list, queue, or other software-defined
                path. For example, when a file system encounters a symbolic
                link file within a path specification, it "chases the
                symbolic link" to redirect operations to the target file.
                See also symbolic link.



























        G-8      Kernel-mode Driver Design Guide        G-8      Kernel-mode Driver Design Guide


        child process        child process
           When a new NT-native process is created by calling a system
           service, the caller must specify a "parent" process from
           which the new process inherits its token, quota, and base
           priority. The new process can optionally inherit any or all
           of the following from the specified parent process:
           n  A copy of the parent's virtual address space.           n
           n  All object handles that were opened with the inheritance           n
              attribute.
           n  Debugging and exception handling ports.           n
           However, an NT user-mode process becomes a wholly
           independent peer to its so-called parent process as soon as
           it has been created. After process creation, any process-to-
           process dependencies become the responsibility of a
           protected subsystem (such as the Win32TM or POSIX
           subsystem).
           A kernel-mode-only (a.k.a. "system") process has no "parent"
           when it is created.

        CID        CID
           Client identifier
              A unique value that identifies a thread.

        class driver        class driver
           a.k.a. "type driver"
              (1) An intermediate driver for a physical device, which
              is connected to a so-called "intelligent controller" such
              as a SCSI HBA, or to an adapter bus. Such a class driver
              communicates with the corresponding port driver according
              to an established protocol, such NT-defined SRBs. The
              system-supplied SCSI disk, CD-ROM, and tape class drivers
              are examples of this type of class driver.
              (2) An intermediate driver that provides system-required
              but hardware-independent support for a given class of
              physical devices. Such a class driver communicates with a
              corresponding hardware-dependent port driver, using a set
              of system-defined device I/O control requests, possibly
              with additional driver defined internal device I/O
              control requests. The system-supplied keyboard and mouse
              class drivers are examples of this type of class driver.

        client/server model        client/server model
           A model for structuring applications or operating systems
           such that the system is divided into processes (servers),
           each of which provides a set of specialized services to
           other processes (clients).

















                            Glossary of Terms and Acronyms      G-9                                 Glossary of Terms and Acronyms      G-9


             collided page fault             collided page fault
                A page fault caused by one thread while an in-page I/O
                operation for another thread is being done on the same page.

             commitment             commitment
                The NT Memory Manager's current value for paging file usage.

             context             context
                The execution state of a thread at any given moment:
                n  For a user-mode thread, the platform-dependent register                n
                   state, kernel stack, TEB, and user stack in the address
                   space of the process to which the thread belongs.
                n  For a kernel-mode thread, the platform-dependent register                n
                   state and kernel stack.
                   Kernel-mode threads have neither a TEB nor a user-mode
                   context, but they must have an associated process. See
                   also process object.
                   Most NT device drivers do not have a context in this
                   sense. Unless a driver (such as an FSD) creates its own
                   process and/or thread(s), it does not have its own stack
                   space or register state. For each driver, the set of
                   objects it owns and the IRPs that it can access via a
                   device queue object associated with its device object can
                   be considered all or part of its context.

             context record             context record
                A system-defined structure, containing the current register
                state for an exception handler. See also SEH.

             control objects             control objects
                A class of Kernel-defined object types, used to manage all
                kernel-mode operations except dispatching and
                synchronization. See also dispatcher objects.
                   Control objects include: APC, DPC, device queue,
                   interrupt and process objects. Note that all control
                   object types except processes are kernel-mode-only
                   objects, invisible to user-mode code. User-mode APC
                   objects are also "invisible" in the sense that they look
                   more like user-supplied routines to be called on return
                   from certain system services (such as a request to read a
                   file) than like objects.

             controller object             controller object
                A kernel-mode-only object type, defined by the I/O Manager.
                A controller object represents a hardware controller or
                channel. The driver calls IoAllocateController to carry out                                          IoAllocateController
                synchronized I/O on attached devices. Controller objects
















        G-10     Kernel-mode Driver Design Guide        G-10     Kernel-mode Driver Design Guide


           "connect" a set of similar devices attached to a controller
           with a single driver.

        critical section        critical section
           A piece of code that accesses a nonsharable resource, such
           as device-state data stored in a device extension to which
           access must be synchronized among some number of driver
           routines.

        DACL        DACL
           Discretionary access control list
              A discretionary ACL is part of the security descriptor
              for an object. It can be applied to a newly created
              object in order to constrain access to the object. See
              also ACE, access right, ACL and security descriptor.

        DCB        DCB
           Directory control block
              An internal FS structure in which a file system maintains
              state for an open instance of a directory file.

        deadlock        deadlock
           A runtime error condition that occurs when two threads of
           execution are blocked, each waiting to acquire a resource
           that the other holds, and both unable to continue running.

        device extension        device extension
           A part of a device object whose size is determined when a
           driver creates the device object and whose internal
           structure is driver-defined. For many NT drivers, a device
           extension is the driver's major (and only) data storage
           area, used to maintain device state and to contain any
           system-defined objects and other data that the driver writer
           decides to use.

        device object        device object
           A kernel-mode-only, I/O Manager-defined object type, used to
           represent a physical, logical, or virtual device whose
           driver has been loaded into the system. Each driver calls
           IoCreateDevice to initialize a device object for each device           IoCreateDevice
           that driver services. See also driver object.
           Devices are "visible" to end users as named file objects,
           stored in a directory protected against careless or
           malicious user-mode access. User-mode code (protected
           subsystems) must access any device through the opaque handle
           returned by the system service that opens the file object
           that represents the device to user-mode code.
















                            Glossary of Terms and Acronyms     G-11                                 Glossary of Terms and Acronyms     G-11


             device queue object             device queue object
                A kernel-mode-only, Kernel-defined control object type, used
                to record the Boolean state (Busy or Not_Busy) of a device
                and to queue I/O requests for subsequent processing. A
                device queue object has an associated executive spin lock.
                   An I/O request, called a "queue entry," is not actually
                   placed in the device queue unless the state is already
                   Busy:
                   n   On the transition from Not_Busy to Busy, the driver                   n
                       is expected to service the queue entry immediately.
                   n   Subsequent requests while the state is Busy are                   n
                       queued in FIFO or key-sorted order.
                   n   An attempt to remove a queue entry from an empty                   n
                       queue causes the transition from Busy to Not_Busy.
                   n   An attempt to remove a queue entry from an empty                   n
                       queue when the device is Not_Busy causes the system
                       to "bugcheck" (i.e., crash).

             directory file             directory file
                A file that points to or lists a set of named file objects.
                   Note that on-disk directory files are represented in NT
                   as file objects, not as object directory objects.

             directory object             directory object
                See object directory object.

             DIRQL             DIRQL
                Device interrupt request level
                   See also IRQL and IDT - This particular IRQL refers to
                   the IRQL at which a given device interrupts.

             dispatch state             dispatch state
                For a thread at any given moment, one of the following:
                n  Initialized.                n                   ____________
                n  Ready - queued and eligible for dispatch to a processor.                n                   _____
                n  Standby - ready and selected to execute, but a context                n                   _______
                   switch to the thread has not yet occurred.
                n  Running.                n                   _______
                n  Waiting - suspended until a particular dispatcher object                n                   _______
                   is set to the Signaled state.
                n  Terminated.                n                   __________

             dispatcher objects             dispatcher objects
                A class of Kernel-defined object types, used to manage
                dispatching and synchronization. See also control objects.
                   Dispatcher objects have a Boolean state (Signaled or Not-
                   Signaled), and are arguments to the wait services or
















        G-12     Kernel-mode Driver Design Guide        G-12     Kernel-mode Driver Design Guide


              Kernel wait routines. Dispatcher objects include:
              events, (kernel-mode-only) mutexes, semaphores, threads,
              and timers.
              Kernel-mode threads synchronize their operations by
              waiting on one or more dispatcher objects, or by waiting
              on other objects, such as user-mode file objects,
              that contain "hidden" kernel-mode dispatcher objects.
              Note that it is a fatal error to wait on a dispatcher
              object at IRQL > APC_LEVEL.

        DMA        DMA
           Direct memory access
              (No different from any other OS.)

        DPC        DPC
           Deferred procedure call
              A DPC is a Kernel-defined control object type,
              representing a procedure that is to be called later. DPCs
              are executed in kernel mode at IRQL DISPATCH_LEVEL (see
              IDT and IRQL).
              A DPC is primarily used when an interrupt service routine
              (e.g., device driver or clock interrupt service routine)
              needs to perform more work but should do so at a lower
              IRQL than the one at which an ISR executes. (Note that
              getting the IRQL lowered back down quickly is important
              for overall system response time.) The ISR, then, can
              request that a procedure be executed at a lower IRQL at a
              later time.

        driver object        driver object
           A kernel-mode-only object representing an NT driver's load
           image, used by the I/O Manager to locate the driver's entry
           points.

        EA        EA
           Extended attribute
              Files have basically four different parts:
              1   Data
              2   File system attributes (such as creation time, other
                  times, FAT attributes, etc.)
              3   Security descriptor
              4   EAs
              EAs are the set of extended information about a file. An
              EA is viewed as an untyped name-value pair that is
              defined by the user. Typical system uses are to store the
              icon for an image, to indicate that the file is a
              symbolic link, etc.
















                            Glossary of Terms and Acronyms     G-13                                 Glossary of Terms and Acronyms     G-13


             EFU             EFU
                Error format utility
                   A utility, supplied by the system, that reads error
                   entries out of an error log file and displays them.
                   Drivers call IoAllocateErrorLogEntry and                                IoAllocateErrorLogEntry
                   IoWriteErrorLogEntry to transfer errors to an error log                   IoWriteErrorLogEntry
                   file; they can supply error buffer translation routines
                   to format entries for display by the EFU.

             EISA             EISA
                Extended industry standard architecture
                   Also, a standard that defines the architecture of (and
                   interface to) the extended PC bus. See also ISA.

             event object             event object
                A user-mode object upon which one or more threads can wait
                until the event is set to the Signaled state. Every user-
                mode event object is implemented through the use of a
                kernel-mode event object.
                A kernel-mode event object is an instance of a Kernel-
                defined dispatcher object type. Each kernel-mode event can
                be classified as either of the following:
                1  When a synchronization event (a.k.a. "autoclearing                          _____________________
                   event") is set to the Signaled state, a single thread
                   that was waiting on the event is released (its dispatch
                   state transitions from waiting to ready, standby, or
                   running), and an autoreset to Not-Signaled occurs.
                2  When a notification event is set to the Signaled state,                          __________________
                   all threads that were waiting on the event are released,
                   and the event remains in the Signaled state until an
                   explicit reset to Not-Signaled occurs.

             exception             exception
                A synchronous error condition, resulting from the execution
                of a particular machine instruction. See also SEH.




























        G-14     Kernel-mode Driver Design Guide        G-14     Kernel-mode Driver Design Guide


        executive        executive
           The collection of components that form the base NT operating
           system. Executive components include the Executive Support,
           Kernel, Memory Manager, Cache Manager, Process Structure,
           Interprocess Communication (LPC and RPC), Object Manager,
           I/O Manager, Configuration Manager, Hardware Abstraction
           Layer, and Security Reference Monitor.  Each executive
           component except the Executive Support, Cache Manager, and
           Hardware Abstraction Layer supplies a specialized set of
           native user-mode system services, and every executive
           component exports a set of kernel-mode functions for use by
           other executive components.
              NT drivers also call kernel-mode functions supplied by
              executive components, including (but not limited to)
              functions beginning with the prefix "Ex" for Ex(ecutive)                                                           Ex
              Support. Other kernel-mode functions of interest to
              drivers begin with the prefixes: Hal, Ke(rnel), Ps (for                                               Hal  Ke        Ps
              Process Structure), Ob(ject), Io, Mm (for Memory                                  Ob        Io  Mm              _       _                                 _
              Manager), Cc (for Cache Manager), Se(curity) and FsRtl                        Cc                      Se             FsRtl              _                 _ _
              (for File System Run-time Library). See also Zw routines.                   _    _      _   _   __
           Note that NT drivers, including kernel-mode device,
           intermediate, and file system drivers, are considered part
           of the NT executive after they are loaded. The "operating
           system" visible to end users is actually a protected
           subsystem that runs in user mode on top of the NT executive;
           the executive is hidden from end users by a subsystem-
           supplied interface that emulates Windows, POSIX, or some
           other operating system.

        FAT        FAT
           File allocation table
              (adjective: an NT-installable file system that was native
              to DOS; also, a type of disk partition)

        fault tolerance        fault tolerance
           An optional feature of the Windows NT operating system
           environment, which includes the end-user-visible Windows
           DiskMan utility supported by an NT-supplied intermediate
           driver that handles disk partition mirroring, striping, and
           volume set management.

        FCB        FCB
           File control block
              An internal FS structure in which a file system maintains
              state for an open file.


















                            Glossary of Terms and Acronyms     G-15                                 Glossary of Terms and Acronyms     G-15


             file object             file object
                A user-mode object that represents an open instance of a
                file, device, directory, or volume that is accessed through
                the file handle returned by a protected subsystem's function
                that calls down to a system service that opens (or creates)
                a file object . Every file handle contains a "hidden"
                kernel-mode event object, so that callers of the I/O system
                services can wait on a file handle.
                At any given moment, several file objects can be associated
                with a single, shared data file, but each such file object
                has a unique handle and maintains an object-specific value
                for the current file pointer.
                   A file object is sometimes called a "persistent object"
                   because the (file, device, directory, or volume) entity
                   that backs any run-time set of file objects is retained
                   across system boots.

             FS             FS
                File system
                   An FS is a file system driver that registers itself with
                   the NT I/O Manager as an active file system. Unlike many
                   other operating systems, NT does not have a particular
                   must-be-resident file system, and several NT file systems
                   can be active at the same time. NT file systems are
                   dynamically located when a volume is mounted or when a
                   remote name is being resolved: the I/O Manager calls the
                   registered FSs in turn until one file system "recognizes"
                   the volume structure or remote name.
                   Examples of NT-supplied file systems are FAT, HPFS, NTFS,
                   CDFS, the LAN Manager redirector, NPFS (named pipe file
                   system), and RAW.

             FSD             FSD
                File system driver
                   The FSD refers to the portion of a driver that executes
                   in the context of the caller, to which an I/O request is
                   dispatched when the request is originally made. The FSD
                   has no process virtual address space and no particular
                   thread context because it operates in the context of
                   whoever happens to call it.
                   An FSD also executes in the context of the lower-level
                   (intermediate or mass storage device) driver's DPC
                   routine when the I/O operation is being completed if the
                   FSD indicated that it should be called upon completion of
                   the IRP.
                   The term FSD normally refers to the DD (device driver)
                   part of a file system driver only when the driver also
















        G-16     Kernel-mode Driver Design Guide        G-16     Kernel-mode Driver Design Guide


              has an FSP associated with it; otherwise, it's called
              simply a device driver.





























































                            Glossary of Terms and Acronyms     G-17                                 Glossary of Terms and Acronyms     G-17


             FSP             FSP
                File system process
                   The FSP usually refers to a set of device-dedicated or
                   system worker threads that aid a file system driver (FSD)
                   in getting work done, but can also refer to a kernel-mode
                   process set up by an FSD. FSP threads are generally used
                   when a file system driver needs a thread context in which
                   to work. An example is when the driver needs to be able
                   to wait without tying up the calling thread. An FSP
                   kernel-mode process is used only when an FSD must have a
                   driver-specific process address space in which its
                   device-dedicated threads execute. (Most NT file system
                   drivers conserve system memory by not creating their own                                                     ___
                   kernel-mode processes.)
                   Communication between the FSD and the FSP threads is
                   performed through the use of a communication region. This
                   region is generally allocated in a device object's device
                   extension and consists of an interlocked queue and a
                   synchronization event. See also device object, device
                   extension, and event object.
                   Note that any NT driver (not just file systems) can
                   create one or more device-dedicated threads or use system
                   worker threads. In particular, an NT driver should create
                   a thread for I/O operations that use synchronization
                   mechanisms (such as events, timers, semaphores, mutexes,
                   etc.) other than spin locks. Such a driver's thread can
                   wait for an indefinite, nonzero interval on a Kernel-
                   defined dispatcher object, but context switches to the
                   thread slow down the driver's I/O operations.

             GUID             GUID
                Globally unique identifier
                   See SID.

             HAL             HAL
                Hardware abstraction layer
                   An NT executive component that provides platform-specific
                   support for the NT Kernel, I/O Manager, kernel-mode
                   debuggers, and lowest-level device drivers. The HAL
                   exports routines that abstract platform-specific hardware
                   details about caches, I/O buses, interrupts, etc. and
                   provides an interface between the platform's hardware and
                   the system software. For example, the HAL implements a
                   routine to map each device driver's bus-relative device
                   interrupt vector to a system-assigned vector with a
                   corresponding platform-specific hardware priority

















        G-18     Kernel-mode Driver Design Guide        G-18     Kernel-mode Driver Design Guide


              (DIRQL), as well as several routines that provide DMA-
              transfer support.

        hardware exception        hardware exception
           See SEH.


























































                            Glossary of Terms and Acronyms     G-19                                 Glossary of Terms and Acronyms     G-19


             HBA             HBA
                Host bus adapter
                   A hardware device that "connects" NT and a SCSI bus. A
                   SCSI HBA driver usually manages the lower layers of the
                   SCSI-II protocol. See miniport driver; see also port
                   driver, class driver, and SCSI.

             HPFS             HPFS
                High performance file system
                   An NT-supplied installable file system

             hyperspace             hyperspace
                A block of virtual memory somewhere in kernel space,
                dedicated to the use of the NT Memory Manager. Every
                instance of a user-mode virtual address space has an
                associated hyperspace area where the Memory Manager
                maintains internal data (such as page table pages and WSLs)
                for the current process. See also kernel space and user
                space.

             IDB             IDB
                Interrupt dispatch block
                   An internal structure used by the NT Kernel.








































        G-20     Kernel-mode Driver Design Guide        G-20     Kernel-mode Driver Design Guide


        IDT        IDT
           Interrupt dispatch table
              A Kernel-defined call table with a platform-dependent
              number of first-level entries (some for DIRQL ISRs) and
              second-level entries for interrupt transfer routines
              (dependent on a first-level ISR). For symmetric
              multiprocessor platforms, the Kernel sets up an IDT for
              each processor. See also multiprocessor machine.
              The NT Kernel reserves eight first-level entries per IDT
              for its own use; the remaining first-level entries can be
              connected to a platform-specific bus interrupt by the HAL
              or to a device interrupt. The Kernel's reserved entries
              (in low-to-high IRQL priority) are defined by the
              following constants:
              n   PASSIVE_LEVEL - execute thread.              n
              n   APC_LEVEL - execute special Kernel APC.              n
              n   DISPATCH_LEVEL - dispatch (execute DPC).              n
              n   WAKE_LEVEL - debugger execution.              n
              n   CLOCK2_LEVEL - interval-timer execution.              n
              n   REQUEST_LEVEL - interprocessor request.              n
              n   POWER_LEVEL - power failure notification.              n
              n   HIGH_LEVEL - machine checks or bus errors.              n
              The set of software and hardware interrupt vectors mapped
              to these constants is platform-dependent, but none can be
              connected to a driver's interrupt object. Note that the
              constants PASSIVE_LEVEL through DISPATCH_LEVEL and
              WAKE_LEVEL correspond to software interrupt vectors.
              DIRQLs for device drivers usually have IRQL priority
              higher than DISPATCH_LEVEL but lower than CLOCK2_LEVEL.

        IFS        IFS
           Installable file system
              See FS.

        integral subsystem        integral subsystem
           A protected subsystem (server) that performs an essential
           operating system task. For NT, this group includes the Local
           Security Authority, the Security Accounts Manager, the
           Session Manager, and the network server. See also protected
           subsystem.























                            Glossary of Terms and Acronyms     G-21                                 Glossary of Terms and Acronyms     G-21


             intermediate driver             intermediate driver
                An intermediate driver processes I/O requests "between" the
                highest-level driver (frequently an FS) and the lowest-level
                driver that controls the hardware device for which the
                request is bound. See also layered driver.
                   Examples of intermediate drivers include the NT ftdisk
                   driver, which supports fault tolerance, and many class
                   drivers.

             interrupt             interrupt
                An asynchronous hardware signal, usually indicating that a
                peripheral device needs service, that is detected by the
                processor. An interrupt causes the processor to save state,
                to branch to a fixed location, and to resume execution at
                that location. See also IDT.

             interrupt object             interrupt object
                A kernel-mode-only, Kernel-defined control object type, used
                to connect a hardware interrupt source (see DIRQL) and an
                ISR to an IDT entry, or to connect an ISR and an interrupt
                transfer routine (dependent on the ISR at its IRQL) to a
                second-level IDT entry.
                Each interrupt object:
                n  Can be associated with a single IDT entry (and,                n
                   therefore, with a single processor in a multiprocessor
                   machine).
                n  Is either LevelSensitive or Latched, depending on the                n
                   platform or device.
                n  Can be one of several interrupt objects associated with a                n
                   given IDT entry if and only if every interrupt object for
                   that entry is of a single type (LevelSensitive or
                   Latched).
                For a second-level IDT entry, an ISR (e.g., for a bus
                adapter) associated with a first-level IRQL routes the
                interrupt to the (device-specific) interrupt transfer
                routine for service via its entry in the IDT.
                When more than one set of interrupt objects are connected to
                the same first-level IDT entry, the corresponding ISRs are
                called in the same order in which they were connected.

             invalid page             invalid page
                A page-sized range of virtual addresses for which a page
                fault occurs when any address in the range is referenced.
                For NT drivers, referencing an invalid page causes a fatal
                page fault unless the driver is running at an IRQL <
                DISPATCH_LEVEL when the reference occurs.

















        G-22     Kernel-mode Driver Design Guide        G-22     Kernel-mode Driver Design Guide


        I/O stack location        I/O stack location
           a.k.a. "stack location"
              An I/O stack location refers to the part of an IRP that
              is allocated for each driver in a chain of layered
              drivers. Each driver owns one of the stack locations in
              the packet and obtains driver-specific information about
              what I/O operation to carry out on the target device,
              using the supplied arguments. It is also used to store
              context about the driver during I/O completion so that
              the driver's I/O completion routine can perform its
              cleanup operations.

        I/O status block        I/O status block
           An I/O status block is a data structure that is part of each
           IRP. An I/O status block serves two purposes:
           1  For asynchronous system calls, it provides the user (or a
              higher-level driver's IoCompletion routine) a way of
              determining whether or not the service worked when the
              IRP is completed.
           2  It also provides more information about why the service
              either worked or did not work.
           The type definition of an I/O status block is as follows:

           typedef struct _IO_STATUS_BLOCK {
              NTSTATUS Status;
              ULONG Information;
           } IO_STATUS_BLOCK, *PIO_STATUS_BLOCK;

           Upon completion of a system service, the Information member
           supplies the caller with more information about what
           actually occurred. For example, this member contains the
           number of bytes actually read from a file after a read
           operation.






























                            Glossary of Terms and Acronyms     G-23                                 Glossary of Terms and Acronyms     G-23


             IPC             IPC
                Interprocess communication
                   In addition to synchronization primitives, the NT system
                   has two defined, message-passing mechanisms for IPC:
                   1   LPC, defining the port object type with a server
                       process that supplies system (port) services to local
                       (using the same physical memory on a single system)
                       client processes.
                   2   RPC, with an NT-supplied runtime library that
                       implements such RPC capabilities as binding a client
                       process in one address space with a server process in
                       another address space and sending necessary messages
                       to make a remote procedure call possible.
                   The system-supplied named pipe file system supports LPC.
                   The NT LAN Manager redirector also implements named pipes
                   as a transport layer to connect clients to application
                   servers (RPC).

             IRP             IRP
                I/O request packet
                   An IRP is the basic I/O Manager structure used to
                   communicate with drivers and to allow drivers to
                   communicate with each other. A packet consists of two
                   different parts:
                   1   Header, or fixed portion of the packet - This is used                       ______     ___________________________
                       by the I/O Manager to store information about the
                       original request, such as the caller's parameters,
                       the address of the device object upon which the file
                       is open, etc. It is also used by drivers for storing
                       such information as the final status of the request.
                       See also I/O status block and device object.
                   2   I/O stack locations - Following the header is a set                       ___________________
                       of I/O stack locations, one per driver in the chain
                       of layered drivers for which the request is bound.
                       Each stack location contains the parameters, function
                       codes, and context used by the corresponding driver
                       to determine what it is supposed to be doing.

             IRQ             IRQ
                A hardware line over which a peripheral device, bus
                controller, other processor, or the Kernel signals a request
                for service to the microprocessor. (IRQ is a common
                abbreviation for "interrupt request lines.") See interrupt.




















        G-24     Kernel-mode Driver Design Guide        G-24     Kernel-mode Driver Design Guide


        IRQL        IRQL
           Interrupt request level
              The hardware priority level at which a given kernel-mode
              routine runs, thereby "masking off" interrupts with
              equivalent and lower IRQL on the processor. Note that
              such a routine can be preempted by any interrupt with a
              higher IRQL. Note also that running at IRQL
              DISPATCH_LEVEL or higher prevents threads (even those
              with the highest real-time priority level) from running
              on the same processor until the current kernel-mode
              routine lowers IRQL. However, running at raised IRQL on a
              given processor has no effect on the IRQL priority of any
              other processor in a symmetric multiprocessor machine.
              See also IDT, interrupt object, IRQ, ISR, multiprocessor
              machine, and priority.

        ISA        ISA
           Industry standard architecture
              Also, a standard defining the architecture of the PC bus
              (a.k.a. "AT bus standard").

        ISR        ISR
           Interrupt service routine
              A routine whose function is to service a device when it
              generates an interrupt.
              An NT driver's ISR executes at raised IRQL, usually at
              the DIRQL of the interrupt object(s) set up for its
              device (i.e., drivers connected to second-level IDT
              entries execute at the IRQL of the first-level entry they
              connect to). Every NT driver's ISR should execute as
              quickly as possible, doing only what is necessary to save
              sufficient state, to make the device stop generating
              interrupts, and to queue a DPC that completes interrupt
              processing at a lower IRQL.

        kernel mode        kernel mode
           The privileged processor mode in which NT executive code
           runs. A driver or thread running in kernel mode has access
           to system memory and hardware. See also user mode.

        kernel space        kernel space
           (a.k.a. "system space")
              A block of virtual memory, dedicated to the use of
              kernel-mode code. Generally, the NT kernel space is a
              range of high-order virtual addresses around one gigabyte
              in size. See also hyperspace, pool memory, and user
              space.
















                            Glossary of Terms and Acronyms     G-25                                 Glossary of Terms and Acronyms     G-25


             key object             key object
                A NT object type defined by the Configuration Manager that
                represents an entry in the configuration registry database.
                See also Registry.

             latched interrupt             latched interrupt
                (a.k.a. "edge-triggered interrupt")
                   An interrupt that occurs at the transition from
                   deasserted to asserted on the IRQ line.

             layered driver             layered driver
                One of a collection of drivers that respond to the same
                IRPs. See also I/O stack location.
                   The term "layered driver" describes the highest-level and
                   lowest-level drivers in a chain of layered drivers that
                   process the same IRPs, along with all intermediate
                   drivers in the chain.

             LBN             LBN
                Logical block number
                   A logical block number identifies a physical block on a
                   disk, using a logical address rather than physical disk
                   values (for cylinder, track, and sector). For a disk with
                   N blocks (a.k.a. "sectors"), the corresponding LBNs are 0
                   through (N - 1). See also MCB and VBN.

             level-sensitive interrupt             level-sensitive interrupt
                An interrupt that occurs when the signal is asserted on the
                IRQ line.

             LPC             LPC
                Local procedure call
                   See also IPC and port object.






























        G-26     Kernel-mode Driver Design Guide        G-26     Kernel-mode Driver Design Guide


        little-endian        little-endian
           Refers to a memory architecture in which the byte layout is
           as follows:
           n  Byte N is the least significant (and, in conventional           n
              layout diagrams, the "rightmost") byte of:
              n   A word composed of bytes N and (N + 1).              n
              n   A double word composed of bytes N, (N + 1), (N + 2),              n
                  and (N + 3).
              n   A K-byte memory entity composed of bytes N, (N +              n
                  1),...,(N + K - 1).
           n  The address of the preceding word, double word, or K-byte           n
              entity is its least significant byte, N.
           Intel microprocessors always support little-endian
           addressing.  A MIPS-based machine can be configured for
           either big-endian or little-endian addressing. For a little-
           endian configuration, the least significant bit of a 16-bit
           short value is the "rightmost" bit at byte N, while the most           short
           significant bit is the "leftmost" bit of byte (N + 1). See
           also big-endian.

        LSA        LSA
           Local Security Authority

        LU        LU
           Logical unit
              From a SCSI-II HBA driver's point of view, a physical or
              virtual peripheral device, addressable through a TID,
              attached to a SCSI bus.

        LUID        LUID
           Locally unique identifier
              See SID.

        MACL        MACL
           Mandatory access control list
              A part of the security descriptor for each object in a
              system with a B1 or higher security rating from the U.S.
              National Computer Security Center.

        map        map
           (1) To translate a virtual or logical address into a
           physical address. See also MDL.
           (2) To alias a bus-relative interrupt vector to a system-
           assigned interrupt vector. See also HAL.



















                            Glossary of Terms and Acronyms     G-27                                 Glossary of Terms and Acronyms     G-27


             MCB             MCB
                Map control block
                   An MCB is a structure provided by the FsRtl (File System                                                         FsRtl                                                                _    _
                   Run-time Library) package to aid NT file systems in                   _   _    _
                   mapping the VBNs for a file to the corresponding LBNs on
                   the disk.

             MDL             MDL
                Memory descriptor list
                   A memory descriptor list uses an array of physical page
                   frame numbers (PFNs) to describe the pages that back a
                   virtual memory range.

             method             method
                A routine supplied with an NT object type that handles
                standard operations (such as open, close, delete, parse,
                dump, and read or reset security attributes) on every
                instance of the object type.

             MIDI             MIDI
                Musical instrument digital interface

             miniport driver             miniport driver
                (1) An HBA-specific driver, linked against the NT-supplied
                SCSI port driver, that drives a SCSI bus.
                (2) A video-adapter-specific driver, linked against the NT-
                supplied video port driver.

             mirror driver             mirror driver
                a.k.a. "shadow driver"
                   An intermediate (layered somewhere between an FSD and a
                   disk DD) device driver whose responsibility is to keep a
                   duplicate of a disk partition.

             mount             mount
                Operation that requests a file system to make a volume
                useable by the I/O Manager. This is done by filling in the
                information in a VPB which indicates the serial number and
                label of the volume, as well as by filling in the pointer to
                the file system's device object that represents the "volume"
                mounted on the real device.






















        G-28     Kernel-mode Driver Design Guide        G-28     Kernel-mode Driver Design Guide


        multiprocessor machine        multiprocessor machine
           A platform with more than one CPU. NT is designed to run on
           multiprocessor machines, usually configured to be:
           n  Homogenous - all CPUs are identical, and either all have           n              __________
              identical coprocessors or none has a coprocessor.
           n  Closely coupled - all CPUs share memory and have uniform           n              _______________
              access to memory.
           n  Symmetric - every CPU can access memory, handle any           n              _________
              interrupt, and access I/O control registers just like
              every other CPU in the system. Note that any version of
              NT that runs on a symmetric multiprocessor machine also
              runs unchanged on a uniprocessor machine based on the                   _________
              same CPU.
              While NT can run on asymmetric platforms, configured with                                  __________
              a master CPU that handles all IRQs and one or more slave
              CPUs as long as the platform is both homogenous and
              closely coupled, the system has been designed to run
              primarily on symmetric multiprocessor platforms because
              SMP machines have better performance characteristics,
              particularly for I/O.

        mutex object        mutex object
           A kernel-mode-only, Kernel-defined dispatcher object type,
           used to provide mutually-exclusive, deadlock-free access to
           a resource.
              A mutex owner (thread) must run exclusively in kernel
              mode while it retains ownership; an attempt to switch to
              user mode while holding a mutex causes a system crash.
              Ownership of a mutex by a given thread has the following
              effects:
              n   Prevents the owning thread's process from leaving the              n
                  balance set.
              n   Raises the owning thread's priority to the the lowest              n
                  real-time priority value if the owning thread's
                  priority is not already higher.
              n   Prevents the delivery of normal kernel-mode APCs.              n
              Each mutex object has an associated level value, and a
              given thread may acquire ownership of a mutex if and only
              if:
              n   The requested mutex is currently unowned.              n
              n   The requesting thread does not already own a mutex of              n                                             ___
                  a (numerically) higher level.
              These requirements, and the requirement that a mutex
              owner run exclusively in kernel mode, prevent deadlocks.
              Note that recursive ownership of a mutex is possible.
              However, any thread that claims a mutex N times must

















                            Glossary of Terms and Acronyms     G-29                                 Glossary of Terms and Acronyms     G-29


                   explicitly release that mutex N times in order to set the
                   mutex to the Signaled state.





























































        G-30     Kernel-mode Driver Design Guide        G-30     Kernel-mode Driver Design Guide


        native services        native services
           See system services.

        NLS        NLS
           National language support
              A set of routines that give applications access to
              locale-specific information. See also Unicode.

        nonpaged pool        nonpaged pool
           See pool memory.

        NTFS        NTFS
           NT file system
              A file system, native to NT, that supports file system
              and file data recovery, extremely large storage media,
              and various other features.

        object        object
           A single, run-time instance of a system-defined object type.
           Objects visible in user mode include process, thread,
           section, file, event, semaphore, key, timer, port, object
           directory, symbolic link, and token objects.
           Many user-mode objects are implemented through the use of a
           corresponding kernel-mode object, including processes,
           threads, events, semaphores, and timers. Other user-mode
           objects contain "hidden" kernel-mode objects, such as the
           event associated with each file object.
              Kernel-mode-only objects include APC, DPC, device queue,
              interrupt, mutex, driver, device, adapter, controller,
              and stream file objects.

        object directory object        object directory object
           A type defined by the Object Manager and used to implement
           hierarchical object names.
              Note that file system directories are implemented as NT
              file objects, not as object directory objects.



























                            Glossary of Terms and Acronyms     G-31                                 Glossary of Terms and Acronyms     G-31


             object type             object type
                An opaque data structure that defines a protected entity
                implemented and manipulated by the operating system. See
                also opaque.
                   Every user-visible object has:
                   n   A type (whose name must be unique).                   n
                   n   Two parts:                   n
                       1  A header operated on by the NT Object Manager.                            ______
                       2  A body operated on by type-specific system                            ____
                          services. For example, the system service that
                          reads a file operates on an open file object.
                   n   A set of standardized rules for object creation,                   n
                       deletion, protection, access, management, and naming.
                   User-visible objects can contain "hidden" kernel-mode
                   objects. For example, a user-mode thread can wait on a
                   file handle because it contains a hidden, kernel-mode
                   event object.
                   Kernel-mode objects are visible to (and directly
                   accessible only by) the executive component that defined
                   a given object type. They are are indirectly accessible
                   to other kernel-mode code through the type-specific
                   functions exported by the defining component (e.g.,
                   KeInitializeDeviceQueue operates on device queue                   KeInitializeDeviceQueue
                   objects).

             opaque             opaque
                Pertains to any data structure (including NT objects)
                defined with a deliberately hidden internal structure that
                is known only to the executive component that defined the
                type. However, the defining component supplies system
                services and, usually, kernel-mode functions to manipulate
                opaque objects. User-mode data types can also be opaque.

             paging file             paging file
                A system file containing the contents of virtual pages that
                have been paged out of memory. See also backing store.

             page frame             page frame
                A block of contiguous physical addresses used to store the
                contents of a virtual page. Note that the virtual page size
                and page frame size are usually identical, but that a page
                frame size is actually microprocessor-dependent.

             paged pool             paged pool
                See pool memory.


















        G-32     Kernel-mode Driver Design Guide        G-32     Kernel-mode Driver Design Guide


        PCR        PCR
           Processor control registers
              An internal data structure in which the Kernel stores
              per-processor information.

        PEB        PEB
           Process environment block

        PFN        PFN
           Page frame number
              Also, the database in which the NT Memory Manager
              maintains information about every physical page in the
              system. Each PFN is an index for a physical page in the
              array of records that makes up the PFN database. See also
              PTE.

        PIO        PIO
           Programmed I/O

        polling        polling
           A pernicious, but sometimes necessary, coding technique that
           wastes CPU cycles in a driver until the physical device
           updates its registers. NT device drivers should never
           implement polling loops and should minimize the interval
           they specify in calls to KeStallExecutionProcessor (no                                    KeStallExecutionProcessor
           longer than 50 microseconds) if they must poll their
           devices.




































                            Glossary of Terms and Acronyms     G-33                                 Glossary of Terms and Acronyms     G-33


             pool memory             pool memory
                Regions located in kernel space from which memory blocks can
                be allocated and deallocated dynamically (some other systems
                call this "heap memory"). The NT Memory Manager creates two
                kinds of pools for system use and for use by drivers via
                Ex(ecutive) Support function calls:                Ex
                1  Paged pool is a based region that can be paged in and out                   __________
                   of a process's working set. Each process has its own set
                   of PTEs that map paged pool into its address space.
                   Touching a page in this pool can cause a page fault at
                   any time, so drivers should allocate only those data
                   structures accessed exclusively at IRQL PASSIVE_LEVEL or
                   APC_LEVEL (see IDT) from paged pool.
                2  Nonpaged pool is a based region for which all processes                   _____________
                   share a set of PTEs. The NT Memory Manager guarantees
                   that nonpaged pool is resident in physical memory at all
                   times; therefore, this region can be accessed from any
                   process's address space without causing a page fault.
                   However, nonpaged pool is a limited system resource.
                Drivers should allocate from paged pool for entities that
                are accessed exclusively at or below IRQL APC_LEVEL. They
                should minimize their usage of nonpaged pool by "saving" it
                for data that must be accessed at or above IRQL
                DISPATCH_LEVEL. Allocations of contiguous or noncached
                memory come from nonpaged pool.
                The Memory Manager allocates entities from both pools using
                a buddy scheme. See also kernel space.

             port object             port object
                An instance of an object type representing a conduit for
                messages between local (server/client) processes. It is used
                in the LPC (Local Procedure Call) model of NT as an object                            _     _         _
                accessible to user-mode processes through system services.
                The server (callee) process defines a named connection port
                object and sets up two (unnamed) communication port objects
                when a client (caller) process connects to the named port.



























        G-34     Kernel-mode Driver Design Guide        G-34     Kernel-mode Driver Design Guide


        port driver        port driver
           (1) An NT-supplied SCSI driver that supports a set of class
           drivers above it and one or more HBA-specific miniport
           drivers, which link themselves to the NT-dependent port
           driver (implemented as a dynamic-link library) and call its
           ScsiPortXxx routines.           ScsiPort                   ___
           (2) An NT-supplied video adapter driver that supports a
           user-level display driver and one or more adapter-specific
           miniport drivers, which link themselves to the OS-dependent
           port driver (implemented as a dynamic-link library) and call
           its VideoPortXxx routines.               VideoPort                        ___
           (3) A lowest-level device driver whose device is a so-called
           "intelligent controller" or a bus adapter. A port driver
           communicates with one or more class drivers according to an
           established protocol and synchronizes access to the
           controller or bus.
           (4) A lowest-level physical device driver that responds to a
           set of system-defined device I/O control requests (and,
           possibly an additional set of driver-defined internal I/O
           control requests) sent down by a corresponding class driver.
           See also class driver and miniport driver.

        POSIX        POSIX
           Portable operating system for (UN)IX

        PRCB        PRCB
           Processor control block           __        _       _
              An extension of the PCR.

        priority        priority
           An attribute of a thread that determines when and how often
           it is scheduled to run. For a running thread, its priority
           falls into either of two classes, each class with 16 levels:
           1  Variable priority class has values in the range 0 to 15.              ________ ______________
              This class is used by most threads.
              Threads with variable priority are always preemptible
              (scheduled to run round-robin with other threads at the
              same level). In general, the Kernel manages a variable-
              priority thread as follows: when the thread is
              interactive with a user, its priority is high (given a
              boost); otherwise, its priority decays (by one level per
              quantum the thread runs) until it reaches its original
              (programmer-defined) base level.
           2  Real-time priority class has values in the range 16 to              ________________________
              31. This class is used by time-critical threads, making
              such a thread preemptible only by a thread with higher
              priority. Note that a thread running at the highest real-
















                            Glossary of Terms and Acronyms     G-35                                 Glossary of Terms and Acronyms     G-35


                   time priority level could be preempted by a special
                   Kernel APC if an APC_LEVEL interrupt occurs.





























































        G-36     Kernel-mode Driver Design Guide        G-36     Kernel-mode Driver Design Guide


        priority boosts        priority boosts
           A set of system-defined constant values, supplied when
           certain device drivers complete an IRP. In general, drivers
           for interactive devices call IoCompleteRequest with a                                        IoCompleteRequest
           device-type-specific priority boost value. The boost is
           added to the priority of the user-mode thread that
           originally requested the I/O operation, in order to
           compensate for that thread's assumed wait on the I/O.

        probe        probe
           To check whether a memory access of a particular kind (e.g.,
           read) to data (e.g., a handle for an object or a buffer) is
           allowed without causing an access violation. Note that user-
           supplied argument values are always probed and captured (on
           the system stack) before an NT system service gets control
           in kernel mode. The system service is responsible for
           probing whatever a captured pointer accesses.

        process object        process object
           A Kernel-defined control object type, representing the
           virtual address space and control information necessary for
           the execution of a set of thread objects. A user-mode
           process object defines the base priority, default affinity,
           and directory table base value for its threads and for any
           child processes it creates. Every user-visible process
           object is implemented through the use of an embedded kernel-
           mode process object.
              A kernel-mode-only process object must be initialized
              before any thread objects that belong to the process.
              At any given moment, a process is either part of the
              balance set (Included) or not (Excluded). A kernel-mode
              process must remain in the balance set as long as any of
              its threads owns a mutex object. Each thread owning one
              or more mutexes continues to run until it releases its
              last mutex, when the thread is suspended. The process is
              not removed from the balance set until every thread has              ___
              released all mutexes.

        protected subsystem        protected subsystem
           A server that performs operating system functions or that
           emulates another operating system, such as WindowsTM or
           POSIX, on top of the NT executive. See also integral
           subsystem.

        PTE        PTE
           Page table entry

















                            Glossary of Terms and Acronyms     G-37                                 Glossary of Terms and Acronyms     G-37


                   The Memory Manager uses a PTE to represent the state of a
                   virtual page.





























































        G-38     Kernel-mode Driver Design Guide        G-38     Kernel-mode Driver Design Guide


        pulse        pulse
           To set an event to the Signaled state, satisfy as many
           waiters on the event as possible, and to reset the event to
           the Not-Signaled state.

        quantum        quantum
           a.k.a. "time slice"
              A brief period of time during which a given thread
              executes in a multitasking operating system.

        quota        quota
           For each process, NT sets a limit on certain system
           resources the process's threads can use, including quotas
           for paging-file, paged-pool, and nonpaged-pool usage, as
           well as for CPU time. As the process's threads run, the
           Kernel subtracts the CPU time used from the quota. The
           Memory Manager "charges quota" against the process as its
           threads use page-file, paged-pool, or nonpaged-pool memory;
           it also updates these values when threads release memory.

        raise an exception        raise an exception
           A deliberate transfer of control to an exception handler
           when an exception occurs. A kernel-mode component, including
           any NT driver, cannot raise an exeception while running at
           IRQL > APC_LEVEL without bringing down the system. See also
           SEH.

        range        range
           A finite and discrete sequence of values. Note that a
           virtual address range can be backed by a set of
           discontiguous physical pages or by a file stored in
           discontiguous sectors on disk.

        RAW        RAW
           An NT-supplied file system that is the "last resort" for all
           NT I/O requests requiring file system support. When the I/O
           Manager calls active NT file systems to mount a volume, RAW
           file system driver is always called last, because it
           recognizes all disk and tape media. However, RAW supplies
           very primitive file handling capabilities. For example, it
           treats the whole disk as a single file and supplies
           physical-disk-level VBN access to the disk.
              RAW is not an acronym.

        redirector        redirector
           An NT (network) file system driver that provides access to
           files on remote machines.
















                            Glossary of Terms and Acronyms     G-39                                 Glossary of Terms and Acronyms     G-39


             region             region
                A range of virtual addresses.
                   When a user-mode caller creates a section or maps a view,
                   it must specify a region. The NT Memory Manager rounds
                   the specified region's starting address down to the
                   nearest host-alignment boundary and rounds its size in
                   bytes up to the next host-page-size boundary.

             registry             registry
                a.k.a. "configuration registry"
                   A database containing configuration and control data for
                   the system, including which file systems and drivers to
                   load at system boot. The NT Configuration Manager exports
                   system services to manipulate registry key objects
                   contained in the database.

             resource             resource
                An entity (such as a device object, file object, section
                object, variable, structure, or buffer) visible to one or
                more processes.
                   In kernel mode, a shared resource is a multiprocessor-
                   safe synchronization mechanism, rather like a gating
                   semaphore with a dynamic limit value. Drivers can use
                   system-supplied Ex(ecutive) Support and/or Rtl (Runtime                                   Ex                         Rtl                                                                   _  _
                   Library) functions to control access to a memory entity,                   _
                   such as a file or database, on a multiple-reader (shared
                   access), single-writer (exclusive access) basis.

             RPC             RPC
                Remote procedure call
                   A call from one process's thread (client) to another's
                   (server) that exists in a different address space,
                   usually on another (networked) machine. See also IPC.

             Rtl functions             Rtl functions
                There are two general sets of (C) Runtime Library functions                                                  _  _    _
                supplied with the NT system, one each for user mode and for
                kernel mode. All NT drivers can call the kernel-mode Rtl                                                                     Rtl
                functions. An NT (highest-level) driver cannot call a user-
                mode Rtl function unless it is executing in the context of                     Rtl
                the user-mode thread that requested the driver's current I/O
                operation.





















        G-40     Kernel-mode Driver Design Guide        G-40     Kernel-mode Driver Design Guide


        run        run
           verb: to execute on a processor.
           noun: (1) within an MCB, a contiguous range of VBNs mapped
           to a contiguous range of LBNs (a.k.a. "extent"); (2) slang
           for a quantum, as in "when the thread is given the run..."

        runtime priority inversion        runtime priority inversion
           A condition that can occur when threads with mismatched
           priority attributes share resources or when a higher
           priority thread waits for a lower priority thread to
           complete some action. Such an inversion occurs whenever:
           n  A high priority thread is blocked, waiting for a lower           n
              priority thread to release a shared resource or to
              complete an action (and probably to set a dispatcher
              object to the Signaled state).
           n  This lower priority thread is also blocked, because many           n
              other higher priority threads are ready for execution, so
              they will be run first.
           Under these circumstances, the waiting high priority thread
           undergoes a runtime priority inversion, because one or more
           lower priority threads will run before it does. Note that
           two threads with mismatched priorities must be very careful
           to avoid deadlocks if they "share" a resource in a mutually
           exclusive manner (that is, only one thread at a given time
           can access the resource). Such a pair of threads should not
           attempt to use a spin lock. See also thread object,
           priority, resource, and deadlock.

        SACL        SACL
           System access control list
              A part of the NT security descriptor for an object, used
              to maintain per object auditing information. See also
              security descriptor, ACE, and ACL.

        SAM        SAM
           Security Account Manager
              An integral subsystem that maintains a database of
              information on user accounts, including passwords, any
              account groups a given user belongs to, the access rights
              each user is allowed, and any special privileges a given
              user has.

        SCSI        SCSI
           Small computer standard interface (pronunciation: "scuzzy")
              NT SCSI drivers are assumed to comply with the ANSI SCSI-
              II standard. In addition, NT supplies an OS-dependent
              SCSI port driver, implemented as a dynamic-link library,
















                            Glossary of Terms and Acronyms     G-41                                 Glossary of Terms and Acronyms     G-41


                   and several device-type-specific class drivers, together
                   with system-defined interfaces to HBA-specific SCSI
                   miniport drivers and additional class drivers.

             section object             section object
                A user-mode object type, representing a memory entity that
                can be mapped onto a range of virtual addresses in a
                process's address space. Note that creating or opening a
                section object does not allocate physical memory. See also
                view.
                An opened section object can be either:
                1  File-backed - The original entity resides as a file on a                   ___________
                   disk.
                2  Page-backed - The original entity resides either in a                   ___________
                   paging file controlled by the Memory Manager or (wholly
                   or partially) in physical memory where storage is page-
                   granular and the page size is microprocessor-dependent.
                   Unnamed sections are not sharable, but a view into an
                   unnamed section can be mapped through the creating
                   process's handle. Named sections are shareable. All
                   sections are inheritable by child processes.

             security descriptor             security descriptor
                A data structure used to hold per-object security
                information, including the object's owner, group, protection
                attributes, and audit information. See also ACE, ACL, SACL
                and SID.

             security violation             security violation
                A user-mode attempt to access an object (by passing its
                handle to a system service) without having the correct,
                granted access rights for the requested operation. See also
                ACE and ACL.
                   Note that the Security component does not check the
                   access rights on object handles used by kernel-mode code.
                   However, the I/O Manager and network server driver can
                   force a security access check on object handles.


























        G-42     Kernel-mode Driver Design Guide        G-42     Kernel-mode Driver Design Guide


        SEH        SEH
           Structured exception handling
              A feature of the NT system, which supports control
              transfers to exception handlers when certain runtime
              exceptions occur. The system traps the following general
              kinds of exceptions:
              1   Hardware-defined faults or traps, such as,
                  n  Access violations (see also access violation).                  n
                  n  Data-type misalignments (such as a 16-bit entity                  n
                     aligned on an odd-byte boundary).
                  n  Illegal and privileged instructions.                  n
                  n  Invalid lock sequences (attempting to execute an                  n
                     invalid sequence of instructions within an
                     interlocked section of code).
                  n  Integer divides by zero and overflows.                  n
                  n  Floating-point divides by zero, overflows,                  n
                     underflows, and reserved operands.
                  n  Breakpoints and single steps (to support                  n
                     debuggers).
              2   System software-defined exceptions, such as,
                  n  Guard-page violations (attempting to load or store                  n
                     data from or to a location within a guard page).
                  n  Page read errors (attempting to read a page into                  n
                     memory and encountering a concurrent I/O error).
                  n  Paging file quota exceeded (attempting to commit                  n
                     backing store for a page currently being removed
                     from a process's working set).
              NT supplies standard exception handlers for data-type
              alignment faults and for ANSI/IEEE Std 754-1985 floating-
              point faults.
              Both user-mode and kernel-mode code can set up custom
              exception handlers using the except, try, and finally                                           except  try      finally
              constructs currently supplied by NT-compatible C
              compilers and supported by NT-supplied Rtl (Run-time                                                     Rtl                                                          _   _
              Library) functions. An exception handler can be              _
              associated with each call frame in the function-call
              hierarchy of a program. A CONTEXT record contains the
              register state for each exception handler.

























                            Glossary of Terms and Acronyms     G-43                                 Glossary of Terms and Acronyms     G-43


             semaphore object             semaphore object
                A user-mode semaphore gates access to resources, allowing
                some maximum number of threads (as specified when the
                semaphore object was created) to access the resources
                protected by the semaphore.
                Each user-mode semaphore also has an associated current
                count, representing how many additional threads can acquire
                the semaphore. When the current count is zero, a thread
                attempting to acquire the semaphore waits (i.e., blocks)
                until the count is incremented (another thread has released
                that semaphore). Every user-mode semaphore object is
                implemented through the use of a kernel-mode semaphore
                object.
                A kernel-mode semaphore is an instance of a Kernel-defined
                dispatcher object type. It has either of two uses:
                1  A counting semaphore gates access to a resource by                     __________________
                   allowing some number of threads (up to a specified limit)
                   to access the resource while the semaphore is set to the
                   Signaled state (semaphore count is nonzero).
                2  A binary semaphore gates access to a single resource, if                     ________________
                   and only if the limit is set to 1 and it is not possible
                   for the semaphore to be over-Signaled (set to the
                   Signaled state when it is already in the Signaled state).
                   A binary semaphore gates exclusive access to a resource.
                   However, using a semaphore with a limit of 1 to gate
                   access is not the same thing as using a mutex:                             ___
                   semaphores have no ownership, deadlocks are possible, and
                   the owner's priority is unaffected.

             server             server
                (1) A process with one or more threads that accept requests
                from client processes. See also client/server.
                (2) An NT-supplied file system driver that provides remote
                access to files, named pipes, comm devices, and print
                devices. It implements the LAN Manager 2.1 SMB (server
                message block) protocol, along with NT-specific extensions.

             Session Manager             Session Manager
                An integral subsystem that starts and keeps track of NT
                logon sessions and serves as an intermediary between the
                Windows NT and other protected subsystems.






















        G-44     Kernel-mode Driver Design Guide        G-44     Kernel-mode Driver Design Guide


        SFD        SFD
           SCSI filter driver
              An add-on driver for a SCSI class device that is layered
              between the system-supplied class driver and the NT SCSI
              port driver. An SFD intercepts requests for a particular
              SCSI peripheral device that has special features (not
              shared by other SCSI devices of its class), or that does
              not accept standard SCSI-II CDBs, in order to set up
              device-specific requests. For other devices of the same
              class on the same bus, an SFD simply passes requests sent
              down from the system-supplied class driver on to the NT
              SCSI port driver.

        SID        SID
           Security identifier
              A value, unique across time and space, that identifies a
              process in the Security system. SIDs can either identify
              an individual process, usually containing a user's logon
              identifier, or a group of processes.

        Signaled        Signaled
           An attribute of Kernel-defined dispatcher objects that
           support synchronization. When the Kernel sets such an object
           to the Signaled state, any threads waiting on the object are
           released from their wait and become elgible for execution.

        single-byte coding scheme        single-byte coding scheme
           A character encoding scheme, such as ASCII, that uses a byte
           to represent each character. See also Unicode.

        SMP        SMP
           Symmetric multiprocessor machine
              See multiprocessor machine.

        spin lock        spin lock
           A spin lock is a low-level, synchronization mechanism
           defined by the NT Kernel. A driver or any other kernel-mode
           component can use a spin lock to synchronize access to a
           shared resource, particularly in a multiprocessor machine.
           When one routine holds a particular spin lock, a second
           routine running on another processor cannot access the
           resource protected by that spin lock until it acquires the
           lock. While a routine attempts to acquire a spin lock, it
           cannot carry out other operations (it spins) until the lock                                                 _____
           has been acquired.
           Note that operations involving system-defined spin locks are
           IRQL-specific to help prevent deadlocks: an interrupt spin                                                       ______________
















                            Glossary of Terms and Acronyms     G-45                                 Glossary of Terms and Acronyms     G-45


                lock can only be acquired while executing at a DIRQL of the                ____
                associated interrupt object; an executive spin lock can only                                                ___________________
                be acquired while executing at DISPATCH_LEVEL IRQL.

             SRB             SRB
                SCSI request block
                   An NT-defined structure, used to communicate I/O requests
                   from a SCSI class driver to the NT-dependent port driver,
                   which relays such request to appropriate HBA-specific
                   miniport drivers.

             stream file object             stream file object
                   A virtual file representing on-disk data associated with
                   a file, some of which might not be part of the physical
                   file that backs a file object. For example, a stream file
                   object makes it possible to cache the EAs or ACL for a
                   file object together with the file's data. See also
                   volume file.

             stripe driver             stripe driver
                   (a.k.a. "striper")
                   An intermediate driver whose job is to get better
                   performance for file accesses than the underlying disk
                   driver can. A stripe driver is layered between the FSD
                   and a disk device driver (or between a mirror driver and
                   the disk driver). It distributes pieces of each file over
                   a set of partitions concurrently, thereby cutting down on
                   synchronous read/write time for the file.

             subject             subject
                The combination of a (security) token and of an associated
                program that may use system services. See also token.

             symbolic link             symbolic link
                (1) An instance of the symbolic link object type,
                representing a "soft alias" that equates one name to another
                within the NT Object Manager's name space.
                (2) A file object with special properties. A symbolic link
                file is recognized as having the following three attributes:
                1  Its FILE_ATTRIBUTE_CONTROL bit is set.
                2  It has an EA whose name is .FAMILY_IDs and whose 128-bit
                   binary value is 42 (decimal).
                3  It has an EA whose name is .SYMBOLIC_LINK_VALUE and whose
                   value is the fully qualified pathname of the target file.
                When a special file of this type is encountered as a
                component of a pathname, rather than opening the file
                itself, the file system is redirected to the target file.
















        G-46     Kernel-mode Driver Design Guide        G-46     Kernel-mode Driver Design Guide


              Note that the I/O Manager does not actually use a
              symbolic link object to implement symbolic link files; it
              uses a file object.




























































                            Glossary of Terms and Acronyms     G-47                                 Glossary of Terms and Acronyms     G-47


             symbolic link object             symbolic link object
                An instance of a type defined by the Object Manager, used to
                translate a reference to one named object into a different
                name.

             system services             system services
                The set of native, user-mode routines exported by the NT
                executive. Each system service has a name of the form
                TwoLettersXxxYyy where:                ________________
                n  TwoLetters is the prefix for all system services.                n                   __________
                n  Xxx is usually a verb, describing the operation of a                n                   ___
                   given service.
                n  Yyy is generally the object type the service operates on.                n                   ___

             system space             system space
                See kernel space.

             system worker threads             system worker threads
                A set of kernel-mode threads provided by the NT Executive
                Support component that NT drivers, particularly FSDs, use to
                get work done within a nonarbitrary thread context. Such a
                driver sets up a work queue item with a driver-supplied
                callback routine that is queued to be run when a system
                worker thread is dispatched for execution by the Kernel. See
                also FSP and thread object.

             TB             TB
                Translation buffer
                   See TLB.

             TEB             TEB
                Thread environment block































        G-48     Kernel-mode Driver Design Guide        G-48     Kernel-mode Driver Design Guide


        thread object        thread object
           A user-mode thread object represents a path of execution
           within the current process. Every user-mode thread object is
           implemented through the use of an embedded kernel-mode
           thread object.
           A kernel-mode thread is an instance of a Kernel-defined
           dispatcher object type. It is the basic schedulable entity
           in the NT system.
           A thread object:
           n  Is dispatched for execution by the Kernel.           n
           n  Has the following properties at any given moment:           n
              1   Dispatch state
              2   Priority
              3   Context
              4   Execution mode (kernel or user)
              5   Affinity
           n  Is "owned by" a process object but can attach itself to           n
              another process's address space.
           Note that most NT drivers usually execute in the context of
           the currently running thread, that is, in an arbitrary
           thread context. While an NT file system driver can create an
           independent process for its own device-dedicated threads,
           FSDs usually avoid setting up a driver-created process in
           order to conserve system memory. FSDs (and other NT drivers)
           can set up device-dedicated (system-process) threads and/or
           FSDs can use system worker threads if they need a driver-
           specific thread context in which to execute. NT drivers use
           kernel-mode Ps (Process Structure) functions to create                       Ps                           _       _
           processes and/or device-dedicated threads, not the Ke(rnel)                                                              Ke                                                      ___
           thread functions. FSDs call routines supplied by the NT
           Executive Support component to use system worker threads.           Ex

        TID        TID
           Target identifier
              One of up to eight target controllers on a SCSI-II bus
              through which peripheral devices are addressable, either
              as numbered TIDs or as logical units (LUs) subordinate to
              a particular TID.

























                            Glossary of Terms and Acronyms     G-49                                 Glossary of Terms and Acronyms     G-49


             timer object             timer object
                A timer object is an instance of a Kernel-defined dispatcher
                object type. User-mode timer objects can be used to
                synchronize the execution of specific actions, optionally an
                APC, with time. Kernel-mode timer objects are used to
                synchronize the execution of specific actions, in particular
                a DPC, with time.
                   When set to a specified interval:
                   n   The timer's state is reset to Not-Signaled.                   n
                   n   The timer is placed in a queue that is ordered                   n
                       according to expiration time.
                   Any thread that waits on the timer is suspended until the
                   timer is set to the Signaled state when its interval
                   expires.
                   Expiration of the specified interval does not determine
                   the end of a wait; the Signaled state does. Then, the
                   Kernel attempts to satisfy as many waiters as possible.
                The I/O Manager also supplies timer functions for drivers to
                use.

             TLB             TLB
                Translation lookaside buffer
                   (Not directly accessible by system software for the i386;
                   otherwise, an on-chip virtual-to-page address translation
                   cache for the i486 and MIPS microprocessors.)

             toaster device             toaster device
                slang: A SCSI peripheral device of an unknown class.

             token object             token object
                A security object type, representing an authenticated user
                process. Every process has an assigned token, which becomes
                the default token for each of that process's threads.
                However, an individual thread can be assigned a token that
                overrides this default.

             trap handler             trap handler
                A body of code in the Kernel to which the processor
                transfers control when an interrupt or exception occurs. The
                trap handler determines the type of condition that caused
                the interrupt or exception and transfers control to an ISR
                or exception handler.

             Unicode             Unicode
                A fixed-width, 16-bit character encoding standard that NT
                uses to provide NLS support for locale-specific natural
                languages. See also NLS.
















        G-50     Kernel-mode Driver Design Guide        G-50     Kernel-mode Driver Design Guide


        user mode        user mode
           The nonprivileged processor mode in which application code,
           including protected subsystem code, executes. User-mode
           threads can only gain access to system data by calling
           system services. See also kernel mode.

        valid page        valid page
           A virtual page that is currently in physical memory. See
           also invalid page.

        user space        user space
           A block of virtual memory, dedicated to the use of the
           current user-mode process. Generally, the NT user space is a
           range of low-order virtual addresses around two gigabytes in
           size. See also hyperspace, kernel space, section object, and
           view.

        VBN        VBN
           Virtual block number
              A virtual block number identifies a block (a.k.a.
              "sector") relative to the start of a file. For a file
              with N blocks of data, the corresponding VBNs are 0
              through (N - 1).

        VCB        VCB
           Volume control block
              An internal NT file system structure in which a file
              system maintains state about a mounted volume.

        VDM        VDM
           Virtual DOS machines
              A protected subsystem that emulates DOS and Windows
              (earlier versions than Windows NT) on top of NT.

        view        view
           A whole or partial mapping of a section object, always
           allocated on a 64K boundary, in the virtual address space of
           a process. Note that mapping a view of a section that is
           backed by an executable image file, in effect, "loads" the
           image. (Except during the system boot process, NT uses
           memory-mapped I/O, rather than a loader, to start program
           execution.)





















                            Glossary of Terms and Acronyms     G-51                                 Glossary of Terms and Acronyms     G-51


             virtual memory             virtual memory
                A logical view of memory that does not necessarily
                correspond to the underlying physical memory structure. For
                example, a given range of virtual addresses might be mapped
                to (and backed by) some number of discontiguous physical
                pages, even though the corresponding virtual pages could be
                accessed as a single, contiguous range.

             VMCB             VMCB
                Volume map control block
                   An opaque structure that stores VBN-to-LBN mappings for a
                   volume file. FSDs can use a set of FsRtl routines to                                                      FsRtl
                   maintain a VMCB for each mounted volume.

             volume file             volume file
                   A virtual file, maintained by certain NT file systems,
                   whose contents map ancillary structures of the on-disk
                   file system. A volume file is a type of stream file.

             VPB             VPB
                Volume parameter block
                   A VPB is a structure that connects a file system's device
                   object to the device upon which the volume is mounted.
                   The file system's device object is actually used to
                   represent the volume (VPB) mounted on the actual device
                   (physical device object). Device objects for physical
                   disks, tapes, CD ROMs, and RAM disks have associated
                   VPBs.

             VRP             VRP
                Video request packet
                   A structure used to communicate device I/O control
                   requests from a Windows NT display driver to its
                   corresponding adapter-specific miniport driver. The NT
                   I/O Manager sets up an IRP in response to a user-mode
                   display driver's I/O control request and calls the NT-
                   supplied video port driver with the IRP. The video port
                   driver uses the IRP to set up a VRP and calls the
                   miniport driver's StartIo entry point with the VRP.

             window turn             window turn
                Turning a window refers to the process of filling an MCB
                with the appropriate retrieval pointers in order to map a
                VBN for a file to an LBN for a disk.



















        G-52     Kernel-mode Driver Design Guide        G-52     Kernel-mode Driver Design Guide


        working set        working set
           The set of physical pages that are resident for a given
           process while it has one or more running threads. See also
           balance set and quota.
              The size of each process's working set is bounded by a
              minimum number of pages (that the NT Memory Manager
              guarantees to be resident while the process has one
              running thread) and by a maximum. However,  NT does not
              necessarily constrain a process's working set to its
              maximum if many free pages are available.

        WORM        WORM
           Write-once, read many

        WSL        WSL
           Working set list
              The set of WSLEs for the current process.

        WSLE        WSLE
           Working set list entry

        zone        zone
           A block of dynamically allocatable and deallocatable storage
           of a specified and fixed size within a block of equivalent
           zones. Each zone within such a block is aligned on a
           platform-dependent boundary, determined by the processor's
           data cache line size. Callers of the Ex(ecutive) Support                                                Ex
           zone functions must synchronize their allocation and
           deallocation of zones within the block.
              For example, the I/O Manager uses zones to implement
              lookaside lists for fast allocation and deallocation of
              IRPs and MDLs.

        Zw routines        Zw routines
           A set of entry points parallel to the NT executive's system
           services. A call to a ZwXxx entry point from kernel-mode                                 Zw                                   ___
           code (including calls from other system services or NT
           drivers) supplies the corresponding system service, except
           the caller's access rights and the arguments to the Zw                                                               Zw
           "alias" are not checked for validity, and the call does not
           cause the previous mode to be set to user mode. It is the
           responsibility of a kernel-mode caller to check all user-
           supplied arguments for validity before such a caller passes
           them on to a ZwXxx entry point. See also system services,                        Zw                          ___
           probe, and SEH.