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Wrap

C/C++ Source or Header | 1988-06-12 | 9.2 KB | 306 lines

/* ** file: idt.h ** ** purpose: This file contains the format of DOS' internal ** data table which may be located via the un- ** documented function call 52h. ** ** This information has been gathered from many ** sources, including public bulletin boards, ** magazine articles, books, and personal ** exploration. One significant source of the ** structure of this mess is Jim Kyle. Through ** his program CVTTRC, downloaded from Compuserve, ** many holes were filled. ** ** author: Bill Parrott ** ** Copyright (c) 1988, Bill Parrott ** All Rights Reserved */ #pragma pack(1) /* ** type definitions */ typedef unsigned char byte; typedef unsigned int word; typedef unsigned long dword; typedef unsigned int segment; typedef struct idt IDT; typedef struct devhdr DEVHDR; typedef struct pdpt PDPT; typedef struct ldt LDT; typedef struct mdb MDB; typedef struct bcb BCB; typedef struct chain CHAIN; typedef struct ifcb IFCB; typedef struct time TIME; typedef struct date DATE; typedef struct psp PSP; /* ** This structure defines a device driver header. Device drivers ** are linked in a chain by MS-DOS during system boot up. The ** sequence of this linkage is: ** ** NUL ** <installable device drivers> ** CON ** AUX ** PRN ** CLOCK$ ** ** Installable device drivers are loaded and appear in the ** sequence encountered in CONFIG.SYS. The NUL device ** header is listed as part of the internal data table ** (below) and may be used as a starting point in the list. */ struct devhdr { DEVHDR far *nextheader; /* address of next header */ word attributes; /* device attributes */ word strategy; /* strategy entry point */ word intrupt; /* interrupt entry point */ byte devname[8]; /* device name */ }; /* ** This is the definition of the internal data table. Its ** address may be found by subtracting 8 from the value ** returned in (bx) from DOS function 52h and combining ** that offset with the segment returned in (es). ** ** This table format is not correct for versions of DOS ** prior to 3.0. */ struct idt { BCB far *curbcb; /* address of current buffer */ MDB far *arena; /* start of memory arena */ PDPT far *pdpt; /* physical drive parameter table */ CHAIN far *ifcb; /* internal file control blocks */ void far *clockdev; /* address of clock device driver */ void far *condev; /* address of console device driver */ word max_ssize; /* maximum allowed sector size */ BCB far *bcbhead; /* start of buffer list */ LDT far *ldt; /* address of logical device table */ CHAIN far *fcbt; /* file control block table */ word nprotfcbs; /* number of protected fcbs (FCBS=?,n) */ byte nphysdrives; /* number of physical devices */ byte nlogdrives; /* number of logical devices (in ldt) */ DEVHDR nuldev; /* NUL device header */ }; /* ** This structure defines the physical device table. An ** individual entry in the table may be obtained by calling ** DOS interrupt 21H with function 32H, (dl) set to the ** drive desired (0=default, 1=A, 2=B, ...). Returned ** value in (al) = FFH if the drive does not exist, else ** 00H, ds:bx points to the desired entry. ** ** The head of the physical device table may be found in ** the internal data table, described above. */ struct pdpt { byte drive; /* Drive: 0=A, 1=B, etc. */ byte dunit; /* Unit within driver (0,1,...) */ word sectorsize; /* bytes per sector */ byte clustersize; /* sectors per cluster - 1 */ byte shift; /* cluster to sector shift */ word bootsectors; /* number of reserved sectors */ byte fats; /* number of file alloc. tables */ word rootsize; /* number of root dir. entries */ word dataoffset; /* sector # of cluster 2 (data) */ word lastcluster; /* number of clusters + 1 */ byte fatsize; /* sectors for FAT */ word diroffset; /* sector number of directory */ DEVHDR far *devheader; /* address of device header */ byte mediabyte; /* media descriptor byte */ byte accessflag; /* 0 if disk has been accessed */ PDPT far *nextentry; /* address of next entry */ }; /* ** This structure defines the logical device table. This ** table is utilized by MS-DOS to keep track of logical ** drives. The number of entries in the table is kept ** in the internal device table (above) in nlogdrives. ** The number of logical drives is set to the higher ** of LASTDRIVE= in CONFIG.SYS or the number of physical ** drives. ** ** Some general observations (not necessarily rules!!): ** ** code == 00 if logical device is invalid ** code == 40 if logical device directly associated with physical device ** code == 50 if logical device is SUBST'ed ** ** flag == 001b if drive is SUBST'ed */ struct ldt { char currentdir[68]; /* current directory for this drive */ byte code; /* ?? 00, 40 or 50 */ PDPT far *pdpt; /* physical device for this logical dev */ word curdir; /* directory sector */ word fubar[2]; /* ?? FFFFh FFFFh */ word flag; /* ?? 0002, 0008, 001b */ }; /* ** This structure defines a memory descriptor. These are used ** by MS-DOS to keep track of allocated memory. The address ** of the first descriptor is found in the idt (above). */ struct mdb { byte type; /* 'M' if descriptor, 'Z' if last one */ segment owner; /* PSP of owner */ word length; /* length of this block (paragraphs) */ }; /* ** This structure defines the buffer control block. The ** information here is incomplete because it comes entirely ** from CVTTRC.C. */ struct bcb { BCB far *nextbcb; /* address of next BCB */ byte logdrive; /* logical drive associated with buffer */ byte action; /* action code */ word logsec; /* logical sectoe # */ byte nfats; /* # of FATs */ byte sectorsperfat; /* sectors per FAT */ PDPT far *pdpt; /* pdpt associated with buffer */ word fubar; /* ?? (probably filler to align buffer) */ byte buffer[512]; /* the buffer */ }; /* ** This structure is used to define the length of a chain of ** internal file control blocks. By itself, it really does ** nothing, however it provides the mechanism for locating ** IFCBs. */ struct chain { CHAIN far *nextchain; /* link to next chain */ word nentries; /* number of entries in this link */ }; /* ** This structure defines the internal file control block ** used by MS-DOS to track open files. The total number of ** these in the internal file control block chain is determined ** by FILES= in CONFIG.SYS. The total number of these in the ** FCB table chain is determined by FCBS= in CONFIG.SYS. */ struct date { unsigned day : 5; /* day (1-31) */ unsigned month : 4; /* month (1-12) */ unsigned year : 7; /* 1980 - year (0-127) */ }; struct time { unsigned second : 5; /* seconds / 2 (0-29) */ unsigned minute : 6; /* minute (0-59) */ unsigned hour : 5; /* hour (0-23) */ }; struct ifcb { word nopens; /* # opens active */ word mode; /* open mode, 0=read, 1=write, 2=r/w */ byte fileattr; /* file attribute (flags) byte */ word devattr; /* device attribute word */ PDPT far *pdpt; /* pdpt associated with file */ word firstcluster; /* 1st cluster of file */ TIME filetime; /* file time */ DATE filedate; /* file date */ dword filesize; /* file size (bytes) */ dword filepos; /* current file position */ word nclusters; /* # of clusters in file */ word curcluster; /* current cluster */ word dirsector; /* directory sector */ byte dirindex; /* index in directory sector */ byte filename[8]; /* file name */ byte fileext[3]; /* file type (extension) */ word fubar[3]; /* ??? */ segment owner; /* PSP of file owner */ word fubar2; /* ??? */ }; /* ** This structure define the program segment prefix. There ** is a PSP associated with every process executing under ** MS-DOS. Note that in this definition, the FCB's are not ** defined. Since no one (I HOPE!) uses these any more, and ** even if they do they generally have to copy them first, ** this shouldn't really be a big hit. */ struct psp { word wmboot; /* program termination (int 20h) */ segment himem; /* segment of end-of-memory */ byte reserved1; /* reserved */ byte calldos[5]; /* far call to DOS function dispatcher */ void (far *termhndlr)(); /* pointer to terminate handler */ void (far *breakhndlr)(); /* pointer to crtl/break handler */ void (far *crithndlr)(); /* pointer to critical error handler */ segment parentpsp; /* PSP of parent process */ byte handles[20]; /* handle table (FF=available) */ segment environment; /* environment block */ byte reserved2[4]; /* reserved */ word nhandles; /* handle table size */ dword phandles; /* handle table address */ byte reserved3[24]; /* reserved */ word int21; /* int 21h DOS call */ byte farret; /* retf */ byte reserved4[9]; /* reserved */ byte fcb1[16]; /* 1st CP/M-style FCB */ byte fcb2[16]; /* 2nd CP/M-style FCB */ byte extra[4]; /* overflow from FCBs */ byte cmdlen; /* length of command line parameters */ byte cmdline[127]; /* command line parameters */ };