Sprite 1984 - 1993/Sprite 1984 - 1993.iso/src/lib/c/etc/Pfs.man

Text File | 1990-06-27 | 19.8 KB | 499 lines

' $Header: /sprite/src/lib/c/etc/RCS/Pfs.man,v 1.1 89/04/06 08:24:45 brent Exp $ SPRITE (Berkeley)
.so \*(]ltmac.sprite
.HS Pfs lib
.BS
.SH NAME
Pfs_Open, Pfs_OpenConnection, Pfs_SetHandler, Pfs_PassFile, Pfs_Close \- Package for servicing pseudo-file-systems.
.SH SYNOPSIS
\fB#include <pdev.h>\fR
.sp
Pfs_Token
.br
\fBPfs_Open\fR(\fIprefix, rootIDPtr, pfsService, clientData\fR)
.br
Pdev_Stream *
.br
\fBPfs_OpenConnection\fR(\fIpfsToken, fileIDPtr, reqBufSize, readBufSize, readBuf, selectBits, pdevService\fR)
.br
int (*
.br
\fBPfs_SetHandler\fR(\fIpfsToken, operation, handler\fP))()
.br
int
.br
\fBPfs_PassFile\fR(\fIpfsToken, streamID\fP)
.br
void
.br
\fBPfs_Close\fR(\fIpfsToken\fP)
.SH ARGUMENTS
.AS Pfs_CallBacks pdevService
.AP char *prefix in
File name prefix of the pseudo-file-system.
.AP Fs_FileID *rootIDPtr in
The server-defined ID of the root.
.AP Pfs_CallBacks *pfsService in
Set of name service call-back procedures.
.AP ClientData clientData in
User-defined data passed to service call-backs.
.AP Pfs_Token pfsToken in
Return value of \fBPfs_Open\fP.
.AP Fs_FileID *fileIDPtr in
Server's identifier for file in pseudo-file-system.
.AP int reqBufSize in
Preferred size for the request buffer.
.AP int readBufSize in
Size of read buffer.  Zero means no read buffering.
.AP char *readBuf in
Optional read buffer, or NULL.
.AP int selectBits in
\fBFS_READABLE\fR, \fBFS_WRITABLE\fR, \fBFS_EXCEPTION\fR
.AP Pdev_CallBacks *pdevService in
Set of pseudo-device service call-back procedures.
.AP int streamID in
A regular open file descriptor returned from \fBopen\fP.
.BE
.SH Pfs_Open
.ta 1.0i 3.0i 3.5i
.LP
\fBPfs_Open\fR declares a server process for a pseudo-file-system
and installs a set of service procedures for it.
The service procedures are called when client processes
do file naming operations on the pseudo-file-system,
i.e. \fBopen\fR, \fBstat\fR, \fBunlink\fR, \fBmkdir\fR, \fBrmdir\fR, \fBrename\fR, and \fBlink\fR.
As a side effect of opening a file in the pseudo-file-system the
server can set up a pseudo-device connection for the open file.
Thus the server can completely implement file system
access to the pseudo-file-system.
.PP
The \fIprefix\fP argument indicates what part of the global file system
hierarchy is controlled by the pseudo-file-system server.
This prefix can be arbitrarily nested in the hierarchy
but there must be a remote link that corresponds to it.
(The command \fBln -r \fIprefix\fR creates a remote link for the prefix.)
The existence of the remote link ensures that the kernel's lookup
algorithm will automatically find the pseudo-file-system server.
The pseudo-file-system is visible across the network as well.
.PP
The \fIrootIDPtr\fP defines the file ID for the root of the pseudo-file-system.
This ID will be presented as the \fBprefixID\fP for pathnames that begin
at the root (prefix) of the pseudo-file-system.  The file ID has the following
format.  The server can define the file ID to fit its own needs.
However, the special type value of -1 is reserved to indicate an
invalid file ID.
.DS
typedef struct {
    int type;
    int serverID;
    int major;
    int minor;
} Fs_FileID;
.DE
.LP
The \fIpfsService\fP procedures are described in detail below.
The \fIclientData\fP argument is passed to all the naming service
procedures.  It is ordinarily used to get
to the state of the pseudo-file-system.
.LP
The return value of \fBPfs_Open\fR is a token for the pseudo-file-system,
which must be used in calls to \fBPfs_OpenConnection\fR,
\fBPfs_PassFile\fP,
\fBPfs_SetHandler\fR, and \fBPfs_Close\fP.
If a pseudo-file-system couldn't be opened, then NULL is
returned and \fBpfs_ErrorMsg\fR contains a string
describing the problem.
.LP
The Pfs package uses the facilities of \fBFs_Dispatch\fR in order to keep
track of the streams associated with the pseudo-file-system and ensure
that Pfs is notified whenever those streams become readable.  In order
to use Pfs, you must also use \fBFs_Dispatch\fR.
.SH Pfs_OpenConnection
.PP
\fBPfs_OpenConnection\fP is used to create open file connections
to the pseudo-file-system indicated by \fIpfsToken\fP.
Open file connections can only be made during an \fBopen\fP call-back.
The open file connection is the same as a connection to a pseudo-device
with the addition of two new requests to handle
\fBfstat\fR, \fBfchmod\fR, and \fBfchown\fR.
The details of using the pseudo-device call-backs are given
in the \fBPdev\fP man page.
.PP
The \fIfileIDPtr\fP is a server-defined identifier for the open file.
The server can set the file ID fields to any values that make sense to it.
However, by convention a type of -1 indicates an invalid fileID.
This special case may occur when handling the \fBrename\fP and
\fBhardLink\fP call-backs.
Note that the file IDs for directories in the pseudo-file-system
may be presented back to the server as a \fBprefixID\fP
that indicates the starting point of the lookup operation.
Thus a process can have a current directory inside the pseudo-file-system
and name files relative to that directory.
.PP
The \fIpdevService\fP parameter is a set of pseudo-device call-backs.
The use of these call-backs is described in detail in the \fBPdev\fP man page.
.PP
The \fIreqBufSize\fP parameter indicates the preferred size of the
request buffer associated with the pseudo-device connection.  This size
determines how many requests can be bufferred before the kernel has to
wait on the server.  A minimum size is enforced by the library, so
zero can be passed to get the default size (about 1 Kbyte).
.PP
The \fIreadBufSize\fP and \fIreadBuf\fP parameters indicate the size
and location of an optional read buffer.
No buffering is indicated by a zero read buffer size.
See the library \fBPdev\fP and device \fPpdev\fP man pages for more details
on using a read buffer.
.SH Pfs_PassFile
.PP
\fBPfs_PassFile\fP is used to pass the open file descriptor of
a regular file back to a client in response to an open request.
If this is done then the pseudo-file-system server sees no further
requests concerning this open file;  the file is handled in
the regular way the by kernel.
.PP
\fBPfs_PassFile\fP exists, but the kernel doesn't support it, yet.
.SH Pfs_Close
.PP
\fBPfs_Close\fP is used to end pseudo-file-system service.
This closes the naming stream to the kernel and frees up any
dynamically allocated storage.  After this call \fIpfsToken\fP
should not be used.
.PP
\fBPfs_PassFile\fP exists, but the kernel doesn't support it, yet.
.SH NAME SERVICE PROCEDURES
.ta 2.0i
.pp
The callbacks are given to \fBPfs_Open\fP as a record
of procedures:
.DS
typedef struct {
    int (*open)();    /* PFS_OPEN */
    int (*getAttr)();    /* PFS_GET_ATTR */
    int (*setAttr)();    /* PFS_SET_ATTR */
    int (*makeDevice)();    /* PFS_MAKE_DEVICE */
    int (*makeDir)();    /* PFS_MAKE_DIR */
    int (*remove)();    /* PFS_REMOVE */
    int (*removeDir)();    /* PFS_REMOVE_DIR */
    int (*rename)();    /* PFS_RENAME */
    int (*hardLink)();    /* PFS_HARD_LINK */
    int (*symLink)();    /* PFS_SYM_LINK */
} Pfs_CallBacks;
.DE
.PP
Any of the elements can
be NULL to indicate that the operation should be handled by
a default handler that is a no-op procedure that returns
a file-not-found error.
The \fIservice\fP parameter to \fBPfs_Open\fP
itself can also be NULL to indicate default
handling for all operations.  This is only useful during initial test.
The global variable \fBpfs_Trace\fP can be set to a non-zero value
to generate printfs to stderr when
each service procedure (default or user-supplied) is invoked.
.PP
All the name service procedures have
a similar calling sequence that includes a relative pathname,
a record containing input parameters,
and a buffer for \fIpathname redirection\fP.
(The \fBrename\fP and \fBhardlink\fP procedures have slighly different
calling sequences because they handle two pathnames.)
The pathname is relative to a prefix indicated
by a \fIprefixID\fR in the input parameters.
This ID is either for the root as defined by
the \fIrootIDPtr\fP argument to \fBPfs_Open\fP,
or for some directory who's ID was defined by \fBPfs_OpenConnection\fP
when the directory was entered by a client process.
.LP
The service procedures should return 0 to mean success,
otherwise they should return a suitable errno value.
There are no other return results.  Open file connections are
created as a side effect using \fBPfs_OpenConnection\fP.
.LP
It is possible that the pathname may leave the pseudo-file-system
during any lookup operation.
This happens with remote links, symbolic links back to the root,
or with enough ``..'' components to take the pathname out the
top of the pseudo-file-system.  In this case the pseudo-file-system
server should return the remaining, or new, pathname instead of
attempting to follow it itself.  The return code \fBEREMOTE\fR is
used to indicate this situation, and the \fIredirectPtr\fP argument is
used to return the new name:
.DS
typedef struct FsRedirectInfo {
    int    prefixLength;
    char fileName[FS_MAX_PATH_NAME_LENGTH];
} FsRedirectInfo;
.DE
.PP
If the lookup hits a symbolic link to the root the server should
expand the link and return the new absolute pathname in this buffer.
A remote link is like a symbolic link, except it indicates a nested
prefix and its contents are the prefix itself.  Expanding it will
result in a new absolute pathname.
The length of the prefix that is embedded in the absolute path
should be returned in the \fBprefixLength\fP
field.  With regular symbolic links this field should be zero.
If the server hits a ``..'' component that leaves its root it should
place the remaining pathname, including the offending ``..'' component,
into the buffer.  The prefix length is again zero in this case.
.SH open
.ta 2.5i
.DS
int
(*service->open)(clientData, name, openArgsPtr, redirectPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    Fs_OpenArgs *openArgsPtr;    /* Identifies prefix and caller */
    FsRedirectInfo *redirectPtr;    /* Return - new pathname and prefix info if
    * name leaves the pseudo-file-system */
.DE
.LP
The open service procedure is invoked in response to an \fBopen\fR system call
by a client process.  The \fIclientData\fP argument is the
value passed into \fBPfs_Open\fR and is generally used to get back to
the state kept for the pseudo-file-system.
The \fIname\fP is a relative pathname that begins at the prefix
indicated by \fI*openArgsPtr\fP.  The \fBFsOpenArgs\fP structure
identifies the root of the pseudo-file-system, the
prefix or starting directory of the pathname,
and the identity of the calling process:
.DS
typedef struct {
    Fs_FileID prefixID;    /* File ID from prefix handle */
    Fs_FileID rootID;    /* File ID of root. */
    int useFlags;    /* Flags defined in fs.h */
    int permissions;    /* Permission bits for created files.  Already
     * reflects per-process permission mask */
    int type;    /* Used to contrain open to a specific type */
    int clientID;    /* Host ID of client doing the open */
    Fs_UserIDs id;    /* User and group IDs */
} FsOpenArgs;
.DE
.LP
The \fBprefixID\fR is either the fileID of the root of the pseudo-file-system,
or the fileID of some directory in the pseudo-file-system that
has been previously opened.
The \fBuseFlags\fP is an or'd combination of flags defined in
<fs.h> that include \fBFS_READ\fR, \fBFS_WRITE\fR, and \fBFS_EXECUTE\fR.
The \fBpermissions\fR define the file mode when creating a file.
File creation is indicated by the \fBFS_CREATE\fR usage flag.
.PP
The \fBtype\fR is used to constrain the open to a particular kind of file.
Possible values are \fBFS_FILE\fR, which means any type will do,
\fBFS_DIRECTORY\fR when changing the current directory,
and \fBFS_SYMBOLIC_LINK\fR when reading links.
.PP
IMPORTANT:  \fBPfs_OpenConnection\fR and
\fBPfs_PassFile\fR can only be called during the servicing of
an open request.  If they are called (successfully) by the open call-back
it must return 0, never a non-zero error status.
.SH getAttr
.ta 2.5i
.DS
int
(*service->getAttr)(clientData, name, openArgsPtr, attrPtr, redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsOpenArgs *openArgsPtr;    /* Bundled arguments */
    Fs_Attributes *attrPtr;    /* Return - attributes of the file */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to get the attributes of a file in the pseudo-file-system
given its pathname.  The arguments are similar to those of the \fBopen\fR
call-back.  The \fIattrPtr\fP argument is used to return the attributes.
.SH setAttr
.ta 0.5i 2.5i
.DS
int
(*service->setAttr)(clientData, name, openArgsPtr, flags, attrPtr,
    redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsOpenArgs *openArgsPtr;    /* Bundled arguments */
    int flags;    /* Specifies which attrs to set */
    Fs_Attributes *attrPtr;    /* New attributes of the file */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to set certain attributes of a file in
the pseudo-file-system
given its pathname.  The arguments are similar to those of the \fBopen\fR
call-back.  Additionally, the \fIflags\fP argument indicates which attributes
are to be set, and the \fIattrPtr\fP argument specifies their new values.
The \fIflags\fP are an or'd combination of
\fBFS_SET_TIMES\fR, \fBFS_SET_MODE\fR, \fBFS_SET_OWNER\fR,
\fBFS_SET_FILE_TYPE\fR, \fBFS_SET_DEVICE\fR.
.SH makeDevice
.ta 2.5i
.DS
int
(*service->makeDevice)(clientData, name, makeDevArgsPtr, redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsMakeDeviceArgs *makeDevArgsPtr;    /* Bundled arguments */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to create a special device file in the
pseudo-file-system.  The \fBFsMakeDeviceArgs\fP are similar to the
\fBFsOpenArgs\fP with some addition information about the device:
.DS
typedef struct {
    Fs_FileID prefixID;    /* FileID of the prefix */
    Fs_FileID rootID;    /* FileID of the root */
    Fs_Device device;    /* Device attributes */
    int permissions;    /* Permissions already reflect per-process mask */
    Fs_UserIDs id;    /* Identifies calling process */
    int clientID;    /* Identifies host of calling process */
} FsMakeDeviceArgs;
.DE
.SH makeDir
.ta 2.5i
.DS
int
(*service->makeDir)(clientData, name, openArgsPtr, redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsOpenArgs *openArgsPtr;    /* Bundled arguments */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to create a directory.  The arguments are similar
to those of the \fBopen\fP call-back.
.SH remove
.ta 2.5i
.DS
int
(*service->remove)(clientData, name, lookupArgsPtr, redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsLookupArgs *lookupArgsPtr;    /* Bundled arguments */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to remove a file in the pseudo-file-system.
\fBFsLookupArgs\fP are a simplified sub-set of \fBFsOpenArgs\fP:
.DS
typedef struct {
    Fs_FileID prefixID;    /* FileID of the prefix */
    Fs_FileID rootID;    /* FileID of the root */
    int useFlags;    /* not used */
    Fs_UserIDs id;    /* User and group IDs of calling process */
    int clientID;    /* Host ID of calling process */
} FsLookupArgs;
.DE
.SH removeDir
.ta 2.5i
.DS
int
(*service->removeDir)(clientData, name, lookupArgsPtr, redirectInfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *name;    /* Relative pathname */
    FsLookupArgs *lookupArgsPtr;    /* Bundled arguments */
    FsRedirectInfo *redirectInfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to remove a directory in the pseudo-file-system.
The server should check against removing non-empty directories.
The arguments are the same as for \fBremove\fP.
.SH rename
.ta .5i 3.0i
.DS
int
(*service->rename)(clientData, srcName, dstName, twoNameArgsPtr,
    redirect2InfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *srcName;    /* Original name */
    char *dstName;    /* New name */
    Fs2PathParams *twoNameArgsPtr;    /* Lookup args plus prefixID2 */
    Fs2PathRedirectInfo *redirect2InfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is made to change the name of a file in the pseudo-file-system.
The arguments are bundled into the \fBFs2PathParams\fP structure:
.DS
typedef struct Fs2PathParams {
    FsLookupArgs lookup;    /* Regular lookup parameters */
    Fs_FileID prefixID2;    /* Prefix of second pathname */
} Fs2PathParams;
.DE
.PP
It is possible that the second pathname is not a part of the pseudo-file-system.
The Sprite kernel still calls out to the pseudo-file-system in this case
because the first pathname might be redirected out of the pseudo-file-system.
If the second prefixID does not belong to the pseudo-file-system
that is indicated by a \fBtype\fP value of -1.
If the first pathname remains in the pseudo-file-system but the second
prefixID is not in the pseudo-file-system
then the error \fBEXDEV\fR should be returned.
If either of the pathnames gets redirected, or an error occurs
during pathname interpretation, the \fBFs2PathRedirectInfo\fP
structure is used to return more information:
.DS
.ta 0.5i 2.0i
typedef struct {
    int name1ErrorP;    /* TRUE if redirection or other error applies
         * to the first pathname, FALSE if the error
         * applies to second pathname, or no error */
    int prefixLength;    /* The length of the prefix embedded in
         * fileName.  This is used when a server hits
         * a remote link and has to return a new file
         * name plus an indication of a new prefix. */
    char fileName[FS_MAX_PATH_NAME_LENGTH];
        /* The new file name.  Returned
         * from the server when its lookup is about
         * to leave its domain. */
} Fs2PathRedirectInfo;
.DE
.SH hardLink
.ta .5i 3.0i
.DS
int
(*service->hardLink)(clientData, srcName, dstName, twoNameArgsPtr,
    redirect2InfoPtr)
    ClientData clientData;    /* Passed into Pfs_Open */
    char *srcName;    /* Original name */
    char *dstName;    /* New name */
    Fs2PathParams *twoNameArgsPtr;    /* Lookup args plus prefixID2 */
    Fs2PathRedirectInfo *redirect2InfoPtr;    /* Used when name leaves our domain */
.DE
.PP
This call-back is used to create a hard link between two files in the
pseudo-file-system.  The arguments are the same as those for \fBrename\fP,
and the same comments about pathname redirection apply.
.SH symLink
.DS
int
(*service->symLink)(clientData, linkName, value, openArgsPtr, redirectInfoPtr)
    ClientData clientData;    /* returned from Pfs_Open */
    char *linkName;    /* SymLink file name */
    char *value;    /* Symlink value */
    FsOpenArgs *openArgsPtr;    /* Open arguments */
    FsRedirectInfo *redirectInfoPtr;    /* Used when srcName leaves our domain */
.DE
.PP
This call-back is used to create a symbolic link in the
pseudo-file-system.  The arguments are similar to those for \fBopen\fP,
except there are two pathnames.
Pathname redirection is only possible on the \fIlinkName\fR.
The \fIvalue\fR pathname is simply used as the value of the link regardless
of its location in the system.
(This is not currently used.  Symbolic links are created instead by
opening a file of type FS_SYMBOLIC_LINK and writing the link value
into it.  This will change, although it currently works in NFS.)
.PP
The \fBtype\fP field in the open args is used differentiate between
a regular symbolic link and a remote link.  A remote link is a circular
symbolic link with a different file descriptor type than a symbolic
link.  Remote links are used in native Sprite file systems to indicate
a nested prefix that is stored elsewhere.  Bumping into a remote link
causes a pathname redirection just like hitting a symbolic link back
to the root.  Additionally, however, the redirection information also
includes the length of the prefix that is embedded into the returned
pathname.
.SH SEE ALSO
pfs (devices), Pdev, Swap_Buffer
.SH KEYWORDS
pseudo-file-system