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RDCF: A Reentrant DOS-Compatible File System, Version 2.0 by Philip J. Erdelsky PLAIN VANILLA CORPORATION CompuServe 75746,3411 InterNet 75746.3411@compuserve.com January 15, 1993 Copyright (c) 1993 Plain Vanilla Corporation 1. Introduction --------------- RDCF is a reentrant and ROMable DOS-compatible file system designed for use with floppy diskettes and hard disk partitions that do not exceed 32 Mbytes in size. For users who are familiar with version 1.0, here is a summary of the differences between versions 1.0 and 2.0: (1) Version 2.0 supports subdirectories and volume names. This is by far the most important difference. (2) Version 2.0 can be compiled to adapt to different sector sizes at run time. (3) Version 2.0 has no default drive option, but it can be compiled with or without multiple drive support. (4) The parameters to some functions have been changed slightly to make them more uniform. (5) Version 2.0 requires access to the system clock, although a dummy access function will suffice for systems without clocks. (6) In version 2.0, the drive access function pointer is stored in the file control block by the calling program, instead of being passed as a parameter. (7) In version 2.0, direct access to the file control block is not encouraged to the extent it was in version 1.0. (8) Version 2.0 has a few additional features, such as a directory sort function, that were not in version 1.0 and are not in most implementations of DOS. (9) Version 2.0 is copyrighted. Although you may use it non-commercially without registering it or paying any fees, resale or commercial use requires permission and payment of a one-time royalty. Although DOS 3 permits characters from the IBM extended character set in file names, most DOS applications don't, and neither does RDCF. Since DOS 1 is now obsolete, RDCF does not support DOS 1 diskette formats. RDCF is fully reentrant with respect to files on different drives. It is also reentrant with respect to files on the same drive, provided they are opened for reading only. It is not reentrant with respect to different files on the same drive, if any of them are being written. Therefore, access to it in this case must be serialized on a drive-by-drive basis when it is used in a multitasking system. RDCF does not call on the memory allocator. All working storage for an open file is contained in a file control block and a scratch buffer that you must allocate in some manner before calling on RDCF. In a manner of speaking, this is a reversion to the old CP/M standard, but it permits complete reentrancy and does not limit the number of open files. Since RDCF treats each open file as though it were the only open file, it cannot detect collisions. For example, in a multitasking system, if a file is written by two tasks at the same time, it will be corrupted. The disk may end up with lost clusters and cross-linked chains, but other files on the same disk should keep their integrity. RDCF requires access to a real-time clock. If your system does not have a real-time clock, you can write a dummy clock interface that always returns some standard date and time, such as the notorious 1/1/80 00:00:00, which will be applied whenever a file is created or modified. RDCF accesses a disk one sector at a time. While this may seem appallingly inefficient, it appears adequate in some cases where only minimal file operations are required. A simple cache system, which is also available from the same source, will improve its efficiency in other cases. With simple interfaces and full source code, you can make other changes that you deem necessary for your own application. RDCF can be compiled as a read-only file system. This eliminates much of the code and is suitable for devices that load operating code and other data from DOS diskettes but do not write anything on them. RDCF can be compiled to handle multiple drives, in which case every file specification must begin with a drive letter (followed by a colon). If your system has only one drive, or if you prefer to handle drive selection outside RDCF, you can compile RDCF without multiple drives, in which case a file specification must NOT begin with a drive letter. The interface to RDCF is not ANSI-compliant, although you could put an ANSI compliant interface on top of it. 2. Compilation Instructions --------------------------- The source code for RDCF 2.0 consists of the files RDCF2.C and RDCF2.H. The header file RDCF2.H should be #included in any source file that calls on the RDCF, because it contains function prototypes and other necessary definitions. Since a DOS diskette contains a number of fields of specific sizes, your C compiler must have types of the same sizes. Here is what is required: type number of bits ----- -------------- char 8 short 16 long 32 int at least 16 If your application is to run on a CPU with "big endian" byte ordering, such as one of the Motorola 68000 series, RDCF will have to do some byte swapping because DOS diskettes contain fields with "little endian" ordering. You can do this by #defining the variable _BIG_ENDIAN. If you do not need to write anything on disk, you can save a great deal of code by #defining the variable RDCF_SYSTEM_READ_ONLY. This eliminates almost all code devoted to writing. If you system has multiple drives, you can #define the variable RDCF_MULTIPLE_DRIVES. In this case RDCF will require each file specification to begin with a drive letter (followed by a colon), and it will pass the drive number to the drive interface. If your application has only one drive, or if it has more than one drive but you want to handle drive selection outside RDCF, leave the variable RDCF_MULTIPLE_DRIVES undefined. In this case a file specification passed to RDCF must NOT begin with a drive letter. All DOS diskettes (and nearly all DOS hard disks) use 512-byte sectors, so the following definition is included in the header file RDCF2.H: #define RDCF_SECTOR_SIZE 512 If you change this value, RDCF won't be compatible with DOS, but it can operate in a consistent manner on disks that it has formatted. If you leave RDCF_SECTOR_SIZE undefined, then RDCF will read the sector size from the bootstrap sector of each disk. This produces less efficient code, because expressions involving the sector size cannot be evaluated at compile time. However, it enables RDCF to adapt itself to different sector sizes at run time. You can cut out the code for any RDCF function that you don't need. The publicly defined functions in RDCF2.C do not call each other, so one or more may be removed without difficulty. For example, if you do only sequential file access, you can cut out the function rdcf_seek(). In fact, RDCF probably has more functions than most applications require. RDCF calls on the following standard C functions and macros, which are widely available and are usually reentrant: isalpha() longjmp() memcmp() memcpy() memset() setjmp() toupper() RDCF presumes that all file specifications are expressed in ASCII and that the C compiler uses ASCII for characters and strings. To prevent identifier conflicts, all publicly defined RDCF labels begin with the characters "RDCF", "_RDCF" or "rdcf". The following public domain packages are usually distributed along with RDCF 2.0: package files --------- ----------------------------- CACHE 1.1 CACHE.C, CACHE.DOC, CACHE.H FILES FILES.C, FILES.COM, FILES.DOC The FILES package contains examples of the use of RDCF. It is also a rather handy diskette utility. 3. Drive Access --------------- RDCF does not read or write disks directly. You must supply it with a pointer to a function that you have written or adapted for this purpose. RDCF then calls this function whenever it needs to read or write a disk sector. The format of the function call is as follows: e = (*drive_access)(write, drive, LSN, buffer); int write; nonzero (true) for a write operation; zero (false) for a read operation unsigned drive; drive (0=A, 1=B, etc) unsigned LSN; logical sector number void *buffer; memory buffer for data unsigned e; 0 for a successful read or write, or an implementation-defined nonzero error code The function is called to read or write only one sector at a time. However, you may want to implement some kind of read-ahead, caching or delayed writing at a lower level to improve efficiency. The function may be required to convert the LSN into side, track and sector numbers, although many disk controllers will make the conversion internally. The layout of LSN's is fairly standard, and is designed to minimize head motion when LSN's are accessed in ascending numerical order. On DOS systems, the conversion is made as follows: sector number = LSN % (number of sectors per track) + 1 side number = (LSN / (number of sectors per track)) % (number of sides) track number = LSN / ((number of sectors per track) * (number of sides)) The sector size, the number of sectors per track and the number of sides are written into the following bytes of LSN 0 (where byte 0 is the first byte): byte contents ---- -------------------------------------- 11 LS byte of number of bytes per sector 12 MS byte of number of bytes per sector 24 LS byte of number of sectors per track 25 MS byte of number of sectors per track 26 LS byte of number of sides 27 MS byte of number of sides If RDCF is to adapt automatically to diskettes of different formats in the same drive, the function (*drive_access)() can simply record these values whenever LSN 0 is read or written and then use them to find other sectors. Notice that LSN 0 is always sector 1 of track 0 on side 0. An error code must be a 16-bit nonzero unsigned value. Its format is implementation-dependent. When RDCF receives a nonzero return value from the function (*drive_access)(), it aborts the current operation, puts the return value into the file control block member called "drive_error" and returns the error code RDCF_DRIVE_ERROR. Error correction and retries, if any, must be implemented at a lower level. If RDCF is used in a reentrant fashion, the function (*drive_access)() must also have the required reentrancy. Here is a drive access function that can be used with Turbo C 2.0 (or a compatible later version of Borland or Turbo C++) under DOS: #include <dos.h> unsigned drive_access(int write, unsigned drive, unsigned LSN, void *buffer) { _SI; _DI; return write ? abswrite(drive, 1, LSN, buffer) : absread(drive, 1, LSN, buffer); } The strange-looking first line of the function goads the compiler into saving and restoring the SI and DI registers, something that absread() and abswrite() should do but don't always do, especially when a drive error is detected. DOS does a little bit of caching when you access disks in this manner. Therefore, you should call bdos(13,0,0) to flush the buffers before returning control to DOS. Otherwise DOS may not recognize the changes RDCF has made. 4. Real Time Clock Access ------------------------- When RDCF needs the date and time, it calls a function as follows: rdcf_get_date_and_time(p); struct rdcf_date_and_time *p; pointer to structure to receive date and time You must write a version of rdcf_date_and_time() for your own system. If your system has no real-time clock, the following function will supply the notorious 1-1-80 00:00:00 as the current date and time: struct rdcf_date_and_time(struct rdcf_date_and_time *p) { static struct rdcf_date_and_time DT = {0,0,0,1,1,1980}; memcpy(p, &DT, sizeof(DT)); } If you run RDCF under DOS and use Turbo C 2.0 (or a compatible later version of Turbo or Borland C++), the following function will supply the date and time taken from the system clock: void rdcf_get_date_and_time(struct rdcf_date_and_time *p) { struct date d; struct time t; int day; getdate(&d); day = d.da_day; gettime(&t); getdate(&d); if (day != d.da_day) gettime(&t); p->month = d.da_mon; p->day = d.da_day; p->year = d.da_year; p->hour = t.ti_hour; p->minute = t.ti_min; p->second = t.ti_sec; } Notice that it is sometimes necessary to read the date and time twice to be sure of getting a consistent reading when the function is called at midnight. DOS files always have dates in the period 1980-2107. 5. The File Control Block ------------------------- All working storage for an open file is contained in a file control block of type "struct rdcf", which is defined in the header file RDCF2.H, and a scratch buffer described below. You must allocate space for file control blocks and scratch buffers before calling on RDCF, since RDCF itself does not call on the memory allocator. The first element of a file control block is a pointer to a scratch buffer with room for RDCF_SECTOR_SIZE unsigned characters. The second element is a pointer to the drive access function defined above. You must initialize these pointers, perhaps as follows: static unsigned char my_buffer[RDCF_SECTOR_SIZE]; static struct rdcf f = {my_buffer, drive_access}; If your implementation has a memory allocator, you can use that instead: struct rcdf f; f.buffer = malloc(RDCF_SECTOR_SIZE); f.drive_access = drive_access; If you leave RDCF_SECTOR_SIZE undefined because your system uses different sector sizes on different disks, the buffer must be large enough to hold the largest sector. If RDCF_MULTIPLE_DRIVES is undefined, but your system has more than one drive, you must also put the appropriate drive number into the member f.drive so that it can be passed to the drive access function. With one exception involving the function rdcf_next_file_information(), neither the scratch buffer contents nor the scratch buffer pointer needs to be maintained from one call on RDCF to the next. However, if RDCF is to be used in a multitasking system, tasks that can call RDCF in a reentrant fashion must use different scratch buffers. In most cases, it is sufficient to allocate one scratch buffer for each drive, and to serialize calls on RDCF for each drive. The drive access function pointer must not be changed while the file corresponding to the file control block is open. You don't have to perform any other initialization on your file control blocks; RDCF does that for you. The file control block for a successfully opened file contains a number of members that you can (safely) read and/or write directly, without calling on RDCF: member permitted access meaning --------------- ---------- ---------------------------------------- buffer read/write pointer to scratch buffer drive_access read/write pointer to drive access function drive read/write drive (0=A, 1=B, etc.) file read file information block, described below position read file pointer drive_error read error when RDCF_DRIVE_ERROR is returned result read result returned by most recent operation Of course, you should write into the "drive" member only if you have left RDCF_MULTIPLE_DRIVES undefined but your system has more than one drive. The file information block is described more fully in Section 6 below. File control blocks of the same format are also used by some RDCF functions for working storage, although nothing more than result codes are returned in them. 6. The File Information Block ----------------------------- The "file" member of a file control block, when filled by RDCF, contains the following information about a file: member meaning --------- --------------------------------------------------- spec[13] name and extension in ASCII, terminated by \0 attribute DOS file attribute byte (see below) date_and_time file date and time first_cluster number of first cluster size file length in bytes (0 for volume or subdirectory) The name and extension are at most eight and three characters long, respectively, they are separated by a period (.) if the extension is non-blank, and they are terminated by a nul (\0). RDCF always converts small letters in file names and extensions to the corresponding capital letters before putting them into the file information block. If the information block represents a volume name, however, then the spec[] member contains the name, which is eleven characters long and may contain small letters and special characters. The date_and_time member is itself a structure with the following members: member meaning range ------ --------- ----------------- second file time 0-58, always even minute file time 0-59 hour file time 0-23 day file date 1-31 month file date 1-12 year file date 1980-2107 The bits of the attribute byte are represented by mnemonics defined in RDCF2.H: #define RDCF_READ_ONLY 0x01 #define RDCF_HIDDEN 0x02 #define RDCF_SYSTEM 0x04 #define RDCF_VOLUME 0x08 #define RDCF_DIRECTORY 0x10 #define RDCF_ARCHIVE 0x20 The file information and date-and-time blocks also appear outside the file control block in some contexts. 7. RDCF File Specifications --------------------------- A file specification under RDCF is almost the same as its DOS counterpart. As in DOS, case is not significant in file specifications. Moreover, every name is truncated to eight characters, and every extension is truncated to three characters. Hence "A:MYPROGRAM.PASCAL", "A:MYPROGRA.PAS", and "a:myprogra.pas" all represent the same file. In a multiple-drive system, the file specification MUST begin with a drive specification (a drive letter followed by a colon). In systems with only one drive, the file specification must NOT begin with a drive letter. If you want to handle drive selection outside RDCF, adjust the drive access pointer and the drive number in the file control block to select the desired drive, and then remove the drive letter and colon from the file specification before calling on RDCF. Since there is no "current directory", the file specification must begin at the root and contain the names of all intermediate subdirectories. The backslash at the beginning of the directory path is superfluous and is NOT used. Hence a file specification such as "C:\UTIL\CHKDSK.COM", which is quite familiar under DOS, is invalid under RDCF. The RDCF specification is "C:UTIL\CHKDSK.COM". For the same reason, RDCF does not permit the special subdirectories "." and ".." in a directory path, but to maintain disk-level compatibility with DOS, it puts them into subdirectories that it creates. A directory specification is the same as a file specification, except that it refers to a subdirectory. Where required, a root directory is represented by a drive specification alone; e.g., "B:" represents the root directory on drive B:. In single-drive systems, the empty string "" represents the root directory. RDCF treats all file and drive specifications supplied to it as read-only strings. They may reside in ROM. 8. The Program Interface ------------------------ The RDCF program interface consists of the following functions: function description --------------------------- ------------------------------------- rdcf_attribute() change a file attribute rdcf_close() close a file rdcf_date_and_time() change a file, volume or subdirectory date and time rdcf_delete() delete a file, volume name or subdirectory rdcf_directory() create a subdirectory rdcf_format() format a disk rdcf_free_space() get disk free space rdcf_get_file_information() get a directory entry rdcf_get_volume() get volume name rdcf_match() match name and extension rdcf_move() move a file or subdirectory rdcf_next_file_information() get next directory entry rdcf_open() open a file rdcf_read() read from a file rdcf_recover() recover erased data rdcf_rename() rename a file or directory rdcf_seek() move a file pointer rdcf_set_file_information() write into a directory entry rdcf_set_volume() write volume name rdcf_sort_directory() sort a directory rdcf_undelete() restore a deleted file rdcf_wipe_drive() wipe out erased data rdcf_write() write into a file There are also four externally defined variables, which for reentrancy must be considered read-only: rdcf_format_360 rdcf_format_1200 rdcf_format_720 rdcf_format_1440 8.1. rdcf_attribute() - Change a File Attribute ----------------------------------------------- The following function call changes a file's attribute byte: e = rdcf_attribute(fcb, filespec, attribute); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 unsigned attribute; new attribute byte int e; 0 if file was successfully modified, or negative error code Only the following attribute bits are affected by this function: RDCF_ARCHIVE RDCF_READ_ONLY RDCF_HIDDEN RDCF_SYSTEM Possible return values are as follows: return value meaning ----------------------- ------------------------------------- 0 successful operation RDCF_DIRECTORY_CONFLICT file name conflicts with subdirectory RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_FORMAT_ERROR corrupt file allocation table RDCF_FILE_NOT_FOUND file not found RDCF_INVALID_SPEC invalid drive or file specification RDCF_INVALID_DIRECTORY nonexistent subdirectory in path If RDCF is compiled as a read-only file system, this function is not defined. 8.2. rdcf_close() - Close a File -------------------------------- If a file has been written or otherwise modified, you must close it in order to update its directory entry. Here is the appropriate function call: e = rdcf_close(fcb); struct rdcf *fcb; pointer to open file control block int e; 0 for a successful operation, or a negative error code The file control block must have been successfully opened by rdcf_open(). If the file has been modified, its date and time will be set to the value returned by rdcf_get_date_and_time(). If a file has not been written or otherwise modified, there is no need to close it, and this function will do nothing to it. If RDCF is compiled as a read-only file system, this function is not even defined. Possible return values are as follows: return value meaning ----------------- -------------------------------- 0 successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk 8.3. rdcf_date_and_time() - Change Date and Time ------------------------------------------------ The following function call changes the date and time of a file, volume name or subdirectory: e = rdcf_date_and_time(fcb, filespec, t); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 struct rdcf_date_and_time *t; pointer to block containing desired date and time int e; 0 if operation was successful, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the file specification for a volume name consists of a drive specification alone, e.g., "A:" for drive A:, "B:" for drive B:, etc. In other cases, the file specification for a volume name is the empty string (""). When the time and date of a subdirectory are changed, the time and date of its special subdirectories "." and ".." are also changed. Possible return values are as follows: return value meaning ----------------------- ---------------------------------- 0 successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_FORMAT_ERROR corrupt file allocation table RDCF_FILE_NOT_FOUND file not found RDCF_INVALID_SPEC invalid drive or file specification RDCF_INVALID_DIRECTORY nonexistent subdirectory in path If RDCF is compiled as a read-only file system, this function is not defined. 8.4. rdcf_delete() - Delete a File, Volume Name or Subdirectory ---------------------------------------------------------------- The following function call deletes a file, volume name or subdirectory: e = rdcf_delete(fcb, filespec); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 int e; 0 if file was successfully opened, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the file specification for a volume name consists of a drive specification alone, e.g., "A:" for drive A:, "B:" for drive B:, etc. In other cases, the file specification for a volume name is the empty string (""). Possible return values are as follows: return value meaning ----------------------- ---------------------------------------- 0 successful operation RDCF_ACCESS_DENIED attempt to delete a read-only file or a subdirectory that is not empty RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_NOT_FOUND file, volume name or directory not found RDCF_INVALID_SPEC invalid drive or file specification RDCF_INVALID_DIRECTORY nonexistent subdirectory in path If RDCF is compiled as a read-only file system, this function is not defined. 8.5. rdcf_directory() - Create a New Subdirectory ------------------------------------------------- The following function call creates a new subdirectory: e = rdcf_directory(fcb, filespec); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 int e; 0 if operation was successful, or negative error code The new directory, and its special subdirectories "." and "..", will bear the current date and time as determined by a call on rdcf_get_date_and_time(). Possible return values are as follows: return value meaning ----------------------- ---------------------------------------- 0 successful operation RDCF_DIRECTORY_CONFLICT name conflicts with file or subdirectory RDCF_DIRECTORY_FULL insufficient directory or data space RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_INVALID_SPEC invalid drive or file specification RDCF_INVALID_DIRECTORY nonexistent subdirectory in path If RDCF is compiled as a read-only file system, this function is not defined. 8.6. rdcf_format() - Format a Disk ---------------------------------- Formatting a disk usually involves two operations, both of which are performed by most DOS formatting utilities for diskettes. The first operation, called physical formatting, divides the tracks up into sectors and writes the necessary sector numbers into them. The sectors are filled with meaningless bytes. RDCF has no provision for physical formatting because the procedure is highly hardware-dependent. The second operation, called logical formatting, writes the required information into the bootstrap sector, the file allocation table, and the root directory. RDCF performs logical formatting with the following function call: e = rdcf_format(fcb, spec, format); struct rdcf *fcb; pointer to file control block char *spec; drive specification ("A:", "B:", etc.), omitted if RDCF_MULTIPLE_DRIVE is undefined struct rdcf_format *format; pointer to descriptor block for desired format int e; 0 if operation was successful, or negative error code The format parameter has any of four values, depending on the type of disk being formatted: value of format physical size density capacity ----------------- ------------- ------- -------- &rdcf_format_360 5-1/4 inch double 360K &rdcf_format_720 3-1/2 inch double 720K &rdcf_format_1200 5-1/4 inch high 1.2M &rdcf_format_1440 3-1/2 inch high 1.44M Logical formatting deletes all files, subdirectories and the volume name. Some of this information can be reconstructed by rdcf_recover() or by special recovery programs if it has not been overwritten. However, all the information becomes inaccessible through normal DOS and RDCF calls. The disk also becomes unbootable and cannot be made bootable with the DOS SYS utility. This function is especially useful if the data storage device is not a DOS-compatible disk. You can use it to format a RAM disk, a portion of a hard disk, or even a file and use it as though it were a disk. The function (*drive_access)() usually needs to be modified, but no other changes are required. If you want to use a nonstandard format, you can make up your own format descriptor block. Here is what is in it: byte contents ---- ------------------------------------------------------ 0 LS byte of number of bytes per sector 1 MS byte of number of bytes per sector 2 number of sectors per data cluster 3 1 4 0 5 number of file allocation tables 6 LS byte of number of root directory entries 7 MS byte of number of root directory entries 8 LS byte of total number of sectors 9 MS byte of total number of sectors 10 unused 11 LS byte of number of sectors per file allocation table 12 MS byte of number of sectors per file allocation table 13 LS byte of number of sectors per track 14 MS byte of number of sectors per track 15 LS byte of number of sides 16 MS byte of number of sides 17 unused 18 unused NOTICE that some two-byte parameters are not aligned on even boundaries. Of course, if you format a disk in a nonstandard manner, DOS may not be able to read it. There are a number of limitations on the parameters to guarantee a self-consistent format that RDCF can use: (1) None of the parameters can be zero (although the MS byte of a two-byte parameter can be zero). (2) The sector size must be a multiple of 32; but if RDCF_SECTOR_SIZE is defined, RDCF ignores this field. (3) The number of root directory entries must be a multiple of the number of entries in a sector. Each entry occupies 32 bytes, so if 512-byte sectors are used, the number of entries per sector is 16. (4) The disk contains the following areas, which must add up to the specified total number of sectors: (a) one bootstrap sector, (b) the specified number of file allocation tables, each containing the specified number of sectors, (c) the root directory, and (d) the data sectors. (5) The number of data sectors must be a multiple of the number of sectors per data cluster. Their quotient is the number of data clusters. (6) The number of data clusters must not exceed 65,517. (6) If the number of data clusters is 4077 or less, then each file allocation table must contain at least 3 bytes plus one and one-half bytes for each data cluster. Otherwise, each file allocation table must contain at least 4 bytes plus 2 bytes for each data cluster. Parameters described as "unused" are not used by RDCF, although they may have meanings on a DOS diskette. The rdcf_format() function makes only a perfunctory consistency check on the parameters. RDCF does not use the number of sectors per track or the number of sides, but the function (*drive_access)() may need them. Possible return values are as follows: return value meaning ------------------------ ----------------------------- 0 successful operation RDCF_DISK_FORMAT_ERROR improper format control block RDCF_DRIVE_ERROR error in writing disk RDCF_INVALID_SPEC invalid drive specification If RDCF is compiled as a read-only file system, this function is not defined. 8.7. rdcf_free_space() - Get Disk Free Space --------------------------------------------- The following function call returns the number of bytes of free space on a disk: n = rdcf_free_space(fcb, char *spec); struct rdcf *fcb; pointer to file control block char *spec; drive specification ("A:", "B:", etc.), omitted if RDCF_MULTIPLE_DRIVE is undefined long n; number of free bytes, or a negative error code If the operation is successful, the number of free bytes is also left in the member fcb->file.size. In the absence of drive errors, the number of free bytes returned by this function is the maximum number of bytes that can be added to an existing file that fills a whole number of data clusters. The number of additional bytes that can be written to existing files may be larger, because each file may have some empty space in its last cluster that is not counted as free by this function. The number of bytes that can be written to a newly created file is also the same as the value returned by this function, except in one peculiar case. If a new file is added to a subdirectory, it may be necessary to add a cluster to the subdirectory to accommodate the new file entry. This cluster is not available for file data. Possible error codes are as follows: return value meaning ---------------------- --------------------------- RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_INVALID_SPEC invalid drive specification 8.8. rdcf_get_file_information() - Get a Directory Entry -------------------------------------------------------- The following function reads a directory entry: e = rdcf_get_file_information(fcb, specs, index); struct rdcf *fcb; pointer to file control block char *filespec; directory specification string, with terminating \0 unsigned index; index of desired entry (0 = first entry, 1 = second entry, etc.) int e; 0 if entry was successfully read, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the directory specification string for the root directory consists of a drive specification alone, such as "D:". Otherwise, the empty string ("") represents the root directory. If the operation is successful, useful information about the file, volume name or subdirectory will be found in the file information block fcb->file. If the return value is RDCF_FILE_NOT_FOUND, the entry represents an erased file, volume name or subdirectory. The first character in the name is invalid but other information is valid and reflects the status of the file, volume name or subdirectory before it was deleted. If the entry represents a volume name or subdirectory, the RDCF_VOLUME or RDCF_DIRECTORY bit will be set in the attribute byte. Entries 0 and 1 in a subdirectory represent the special directory entries named "." and "..". RDCF makes no use of these special entries, but it faithfully emulates this DOS feature. The value RDCF_DIRECTORY_FULL is returned if the index would put the entry beyond the end of the directory area, or if the entry lies inside this area but has never been used since the directory was created. In either case, the entry is invalid and there are no valid entries with any higher index value. Even if the entry is valid and represents a file, the file control block may not be used to read, write or otherwise manipulate the file until it is successfully opened by rdcf_open(). If you call this function repeatedly to scan the directory, you should probably use some kind of caching. Otherwise, both the bootstrap block and the directory will be read from disk with each function call. Even without caching, this function produced acceptable results when used to display a directory listing of a floppy diskette, although the process was a little slower than most people would prefer. The companion function rdcf_next_file_information(), which is described below, can also be called to obtain the following entry without repeating the entire directory search. Possible return values are as follows: return value meaning ---------------------- ------------------------------ 0 successful operation RDCF_DIRECTORY_FULL index is past end of directory RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_FILE_NOT_FOUND entry represents deleted file RDCF_INVALID_SPEC invalid drive specification RDCF_INVALID_DIRECTORY nonexistent subdirectory in path 8.9. rdcf_get_volume() - Get Volume Name ---------------------------------------- The following function call scans the root directory for the volume name, if any: e = rdcf_get_volume(fcb, char *spec); struct rdcf *fcb; pointer to file control block char *spec; drive specification ("A:", "B:", etc.), omitted if RDCF_MULTIPLE_DRIVE is undefined int e; 0 if volume name was successfully read, or negative error code If the operation is successful, information regarding the volume name is left in the file information block fcb->file. Possible return values are as follows: return value meaning ---------------------- ------------------------------ 0 successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_FILE_NOT_FOUND disk has no volume name RDCF_INVALID_SPEC invalid drive specification 8.10. rdcf_next_file_information() - Get Next Directory Entry ------------------------------------------------------------- The following function reads the next directory entry after the one read by the most recent call on rdcf_get_file_information() or rdcf_next_file_information() using the same file control block: e = rdcf_next_file_information(fcb); struct rdcf *fcb; pointer to the same file control block used by a previous call on this function or rdcf_get_file_information() int e; 0 if entry was successfully read, or negative error code The file control block and scratch buffer must be the same ones used by the preceding call on rdcf_get_file_information() or this function, and the directory structure on the disk must not have changed. The preceding call must not have returned RDCF_DIRECTORY_FULL. This function uses information left in the file control block to find the next directory entry without rescanning the directory. If the operation is successful, useful information about the file, volume name or subdirectory will be found in the file information block fcb->file. If the return value is RDCF_FILE_NOT_FOUND, the entry represents an erased file, volume name or subdirectory. The first character in the name is invalid but other information is valid and reflects the status of the file, volume name or subdirectory before it was deleted. If the entry represents a volume name or subdirectory, the RDCF_VOLUME or RDCF_DIRECTORY bit will be set in the attribute byte. Entries 0 and 1 in a subdirectory represent the special directory entries named "." and "..". RDCF makes no use of these special entries, but it faithfully emulates this DOS quirk. The value RDCF_DIRECTORY_FULL is returned if the index would put the entry beyond the end of the directory area, or if the entry lies inside this area but has never been used since the directory was created. In either case, the entry is invalid and there are no valid entries with any higher index value. Even if the entry is valid and represents a file, the file control block may not be used to read, write or otherwise manipulate the file until it is successfully opened by rdcf_open(). Possible return values are as follows: return value meaning ---------------------- ------------------------------ 0 successful operation RDCF_DIRECTORY_FULL index is past end of directory RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_FILE_NOT_FOUND entry represents deleted file 8.11. rdcf_match() - Match Name and Extension --------------------------------------------- The following function determines whether a DOS file name and extension match a DOS pattern, which may include the special characters ? and *: match = rdcf_match(name_extension, pattern); char *name_extension; DOS name and extension, with separating . and terminating \0 char *pattern; DOS name and extension, with separating . and terminating \0, possibly including the special characters ? and * int match; true (nonzero) if the name and extension match the pattern; false (zero) otherwise The function follows all the usual DOS quirks. Small letters are converted to capital letters before comparison. The name is truncated to eight characters, and the extension is truncated to three characters. The function does not check the validity of the name and extension or the pattern. 8.12. rdcf_move() - Move a File or Subdirectory ----------------------------------------------- The following function call moves a file or subdirectory from one directory to another ON THE SAME DRIVE: e = rdcf_move(fcb, old_filespec, new_filespec); struct rdcf *fcb; pointer to file control block char *old_filespec; old file specification string, with terminating \0 char *new_filespec; new file specification, with terminating \0 int e; 0 if file was successfully opened, or negative error code The new file specification may not begin with a drive specification, even if RDCF_MULTIPLE_DRIVE is defined. However, it may, and often does, begin with a directory path. The file name and extension in the new file specification need not be the same as those in the old file specification. The file or subdirectory can be renamed as it is moved. The file or directory entry in the old position will be marked as deleted. You may use this function to move a subdirectory, but you must be careful not to corrupt the tree structure by moving a subdirectory into itself or one of its subdirectories. RDCF will not protect you from such folly. Possible return values are as follows: return value meaning ----------------------- ------------------------------------------ 0 successful operation RDCF_DIRECTORY_FULL insufficient directory space for new entry RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_NOT_FOUND file not found RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification RDCF_RENAMING_ERROR new file specification is already in use If RDCF is compiled as a read-only file system, this function is not defined. 8.13. rdcf_open() - Open a File ------------------------------- The following function call opens a file: e = rdcf_open(fcb, filespec, mode); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 unsigned mode; file mode (not used if RDCF is read-only) int e; 0 if file was successfully opened, or negative error code If the file is successfully opened, the file pointer is set to the beginning of the file and the file control block is initialized for use by other RDCF operations on the file. The file information block fcb->file then contains meaningful information about the file. The mode may be as follows: mode operation --------------- ------------------------------------------------ RDCF_CREATE create file for writing, deleting the file if it already exists RDCF_READ open file for reading only RDCF_READ_WRITE open file for reading and writing In read-only file systems, RDCF_READ is the only mode permitted, so the mode parameter is absent. You may wish to open a file in the RDCF_READ mode merely to obtain information from its file control block. Then you can abandon or re-use the file control block; there is no need to close the file. You can emulate the full panoply of DOS open() modes by calling this function more than once. Possible return values are as follows: return value meaning ----------------------- ---------------------------------------------- 0 successful operation RDCF_ACCESS_DENIED attempt to write a read-only file RDCF_DIRECTORY_CONFLICT file name conflicts with subdirectory RDCF_DIRECTORY_FULL insufficient directory space to create a file RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_NOT_FOUND file not found in RDCF_READ or RDCF_READ_WRITE RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification RDCF_MODE_ERROR invalid mode 8.14. rdcf_read() - Read from a File ------------------------------------ The following function call reads a block of bytes from an open file: n = rdcf_read(fcb, buffer, count); struct rdcf *fcb; pointer to open file control block void *buffer; memory buffer to receive data int count; number of bytes to be read int n; number of bytes actually read, or a negative error code The file control block must have been successfully opened in mode RDCF_READ or RDCF_READ_WRITE by rdcf_open(). Reading starts at the current file pointer position. If the operation is successful, the file pointer is advanced to the byte immediately following the last byte read. The return value is the number of bytes actually read. If this nonnegative but less than the count, the end of the file was encountered. Errors are indicated by the following negative return values: return value meaning ---------------------- ------------------------------------------ RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_FILE_FORMAT_ERROR corrupt file allocation table RDCF_MODE_ERROR file mode not RDCF_READ or RDCF_READ_WRITE 8.15. rdcf_recover() - Recover Erased Data ------------------------------------------ The following function call creates a new file and puts all unused data clusters into it: e = rdcf_recover(fcb, filespec); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 int e; 0 if file was successfully opened, or negative error code When a file is deleted by DOS or RDCF, the information contained in the file is not actually erased. The data clusters containing the information are merely marked as unused. Until these clusters are actually used for other files, the information is still there, and can be recovered and assembled into a single file by calling this function. The file specifications must be for a new file. If you try to use an existing file, this function will return the error code RDCF_ACCESS_DENIED. If you specify a file in a subdirectory, it will NOT be lengthened to accommodate the new file, as it would be when you call rdcf_open(). That would destroy information and partially defeat the purpose of this function. If there is no empty space in the subdirectory, this function will return the error code RDCF_DIRECTORY_FULL. If this function is successfully called, the new file will contain all the data in all unused clusters on the specified drive. Of course, the unused clusters will no longer be unused, and the drive will then be completely full. If you want to edit the information, you may have to copy the file to another drive that has room for the backup and scratch files that most text editors require. Some kind of editing is usually required because the new file will typically contain information from a number of old deleted files or subdirectories, and the information will be slightly mixed up if the old files were fragmented. Possible return values are as follows: return value meaning ----------------------- ----------------------------------- 0 successful operation RDCF_ACCESS_DENIED attempt to use an existing file RDCF_DIRECTORY_FULL insufficient directory space RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification If RDCF is compiled as a read-only file system, this function is not defined. 8.16. rdcf_rename() - Rename a File or Subdirectory --------------------------------------------------- The following function call changes the name and/or extension of a file or subdirectory: e = rdcf_rename(fcb, old_filespec, new_filespec); struct rdcf *fcb; pointer to file control block char *old_filespec; old file specification string, with terminating \0 char *new_filespec; new name and extension, with terminating \0 int e; 0 if file was successfully opened, or negative error code The new file specification may not begin with a drive specification or directory path. Possible return values are as follows: return value meaning ----------------------- ---------------------------------------- 0 successful operation RDCF_ACCESS_DENIED attempt to rename a hidden or system file RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_NOT_FOUND file not found RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification RDCF_RENAMING_ERROR new file specification is already in use If RDCF is compiled as a read-only file system, this function is not defined. 8.17. rdcf_seek() - Move a File Pointer --------------------------------------- The following function call moves a file pointer: e = rdcf_seek(fcb, offset); struct rdcf *fcb; pointer to open file control block unsigned long offset; desired file pointer offset, relative to beginning of file int e; 0 for a successful operation, or a negative error code The file control block must have been successfully opened by rdcf_open() in any mode. If the operation is successful, the function returns zero. The next call on rdcf_read() or rcdf_write() will start at the specified position, relative to the beginning of the file. The file control block entry fcb->position or fcb->file.size can be used to convert an offset from the file pointer or end of file to an offset from the beginning of the file. A file cannot be lengthened by moving the file pointer past the end of the file. To lengthen a file, you must move the file pointer to the end of the file and then write enough data to it to make it the desired length. Possible return values are as follows: return value meaning ----------------- ------------------------- 0 successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_SEEK_OUT_OF_RANGE offset exceeds file size 8.18. rdcf_set_file_information() - Set File Information -------------------------------------------------------- The following function writes new information into a directory entry: e = rdcf_set_file_information(fcb, filespec, index, p); struct rdcf *fcb; pointer to file control block char *filespec; directory specification string, with terminating \0 unsigned index; index of desired entry (0 = first entry, 1 = second entry, etc.) struct rdcf_file_information *p; pointer to block with new directory information int e; 0 if entry was successfully written, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the directory specification string for the root directory consists of a drive specification alone, such as "A:". Otherwise, the empty string ("") represents the root directory. This function takes a block of information, converts it to DOS directory format, and writes it into the specified directory entry. The block of information is usually supplied by rdcf_get_file_information. This function is used almost exclusively for special disk utilities. If p->spec[0] is zero, the entire entry will be cleared to zeros. This function will not lengthen a subdirectory if the index is past its current end. Possible return values are as follows: return value meaning ----------------------- ---------------------------------------- 0 successful operation RDCF_DIRECTORY_FULL index is past end of directory RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification If RDCF is compiled as a read-only file system, this function is not defined. 8.19. rdcf_set_volume() - Write Volume Name ------------------------------------------- The following function writes a new volume name: e = rdcf_set_volume(fcb, drive_name); struct rdcf *fcb; pointer to file control block char *drive_name; string of form "d:name" that specifies drive and name, with terminating \0 int e; 0 if name was successfully written, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the string drive_name begins with a drive specification (a drive letter, followed by a colon). Otherwise, it contains only the volume name. In any case, it is terminated by \0. If the volume name is less than 11 characters long, RDCF will pad it with blanks at the end before writing it to the disk. Notice that the volume name may contain small letters, which are NOT converted to capital letters by RDCF. Volume names in DOS are case-sensitive. RDCF will reject the volume name and return RDCF_INVALID_SPEC if the first character of the name is 0xE5, which indicates a deleted file or volume name. If there is already a volume name on the drive, it is replaced by the specified one. The new volume name will bear the current date and time as determined by a call on rdcf_get_date_and_time(). return value meaning ---------------------- ----------------------------------- 0 successful operation RDCF_DIRECTORY_FULL insufficient directory space RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading disk RDCF_INVALID_SPEC invalid drive specification or name If RDCF is compiled as a read-only file system, this function is not defined. 8.20. rdcf_sort_directory() - Sort a Directory ---------------------------------------------- The following function call sorts a directory: e = rdcf_sort_directory(f, filespec, mode); struct rdcf *fcb; pointer to file control block char *filespec; directory specification string, with terminating \0 int mode; code to indicate the kind of sort int e; 0 if directory was successfully sorted, or negative error code If RDCF_MULTIPLE_DRIVE is defined, the directory specification string for the root directory consists of a drive specification alone, such as "A:". Otherwise, the empty string ("") represents the root directory. The sorting mode may be any ONE of the following: mode manner of sort ------------------- --------------------------------------------- RDCF_EXTENSION_NAME sort by extension, then among files that have the same extension, sort by name RDCF_NAME_EXTENSION sort by name, then among files that have the same name, sort by extension RDCF_DATE_TIME sort by date and time (earlier files first) RDCF_SIZE sort by size (smallest files first) The modifier RDCF_REVERSE may be added to any of these modes to sort in the opposite order. For example, RDCF_SIZE+RDCF_REVERSE sorts the files by size, but it puts the largest files first. Actually, before the function sorts the directory entries, it first divides them into five groups and arranges them in the following order: (1) The two system files at the beginning of the root directory and the two special files "." and ".." at the beginning of a subdirectory are always left where they are. (2) The volume label, if any, is put next. (3) The subdirectory entries, if any, are sorted and put next. (4) The file entries are sorted and put next. (5) The entries for deleted files, volume labels and subdirectories, if any, are sorted and put last. Within each category, if two entries are identical according to the sorting criterion, their relative position is left unchanged. Some kind of caching is strongly recommended when using this function. The sorting algorithm is rather primitive one called a "bubble sort", so it may take a noticeable amount of time to sort a long directory, even with caching. Possible return values are as follows: return value meaning ----------------------- ---------------------------------------- 0 successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification If RDCF is compiled as a read-only file system, this function is not defined. 8.21. rdcf_undelete() - Restore a Deleted File ---------------------------------------------- When you delete a file, with either DOS or RDCF, the information in the file is not erased, although it may become rather difficult to find. The following function call restores the original contents of a deleted file, to the extent possible: e = rdcf_undelete(fcb, filespec); struct rdcf *fcb; pointer to file control block char *filespec; file specification string, with terminating \0 int e; 0 if file was even partially recovered, or negative error code The function will attempt to restore as much of the file as possible. If only part of the file can be restored, the value in fcb->position will indicate how much of the file was NOT restored. If the entire file was restored, this entry will be zero. If nothing can be restored because the first data cluster of the file is in use by another file, the function will return RDCF_UNRECOVERABLE_FILE. Even an apparently successful restoration may not restore the original file contents. For example, if another file was written over the original file contents and then deleted, RDCF may have no way of knowing that the file contents have changed. Complete restoration of a file can be assured if the original file was unfragmented before it was deleted and nothing has been written to the disk after it was deleted. Possible return values are as follows: return value meaning ----------------------- --------------------------------------- 0 fully or partially successful operation RDCF_DIRECTORY_FULL index is past end of directory RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_NOT_FOUND entry did not represent a deleted file RDCF_INVALID_DIRECTORY nonexistent subdirectory in path RDCF_INVALID_SPEC invalid drive or file specification RDCF_UNRECOVERABLE_FILE none of the file can be restored If RDCF is compiled as a read-only file system, this function is not defined. 8.22. rdcf_wipe_disk() - Wipe Out Erased Data --------------------------------------------- The following function call writes nonsense over all unused clusters of the specified drive: e = rdcf_wipe_disk(fcb, spec); struct rdcf *fcb; pointer to file control block char *spec; drive specification ("A:", "B:", etc.), omitted if RDCF_MULTIPLE_DRIVE is undefined int e; 0 if operation was successful, or negative error code When a file is deleted by DOS or RDCF, the information contained in the file is not actually erased. The data clusters containing the information are merely marked as unused. Until these clusters are actually used for other files, the information is still there, and can often be recovered by calling rdcf_undelete() or rdcf_recover() or by using a file recovery utility. For security reasons, you may want to make sure your erased files are really erased. This function does that by writing nonsense into every cluster marked as unused. The information is not completely destroyed. It may be possible to read some of it by subjecting the disk to a special analysis in a laboratory, but it cannot be read by an ordinary file recovery utility. Even erasing every unused cluster won't necessarily remove all the information from erased files. There may be unused sectors at the ends of files that are not erased. The last cluster of such a file is not marked as unused, because part of it is being used. But the part that is not being used may contain information from an older file that did use the entire cluster. Possible return values are as follows: return value meaning ----------------------- ------------------------------------------ 0 fully or partially successful operation RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_INVALID_SPEC invalid drive specification If RDCF is compiled as a read-only file system, this function is not defined. 8.23. rdcf_write() - Write to a File ------------------------------------ The following function call writes a block of bytes to an open file: n = rdcf_write(fcb, buffer, count); struct rdcf *fcb; pointer to open file control block void *buffer; memory buffer to supply data int count; number of bytes to be written int n; number of bytes actually written, or a negative error code The file control block must have been successfully opened in mode RDCF_CREATE or RDCF_READ_WRITE by rdcf_open(). Writing starts at the current file pointer position. If the operation is successful, the file pointer is advanced to the byte immediately following the last byte written. If necessary, the file is lengthened to accommodate the bytes being written. The return value is the number of bytes actually written. If this is nonnegative but less than the count, there was insufficient disk space to write all the data. Other errors are indicated by the following negative return values: return value meaning --------------------- -------------------------------------------- RDCF_DISK_FORMAT_ERROR disk improperly formatted RDCF_DRIVE_ERROR error in reading or writing disk RDCF_FILE_FORMAT_ERROR corrupt file allocation table RDCF_MODE_ERROR file mode not RDCF_CREATE or RDCF_READ_WRITE This function also sets an internal flag to indicate that the file has been written, which causes RDCF to update the directory when the file is later closed. If the count is zero, setting the flag is all it does. 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