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============== Function 21, subfunction 7 - set HD base. =============

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The HD base defines hard disk to write with usage of obsolete

syntax /HD in obsolete function 58; at usage of modern syntax

/HD0,/HD1,/HD2,/HD3 base is set automatically.

Parameters:

  * eax = 21 - function number

  * ebx = 7 - subfunction number

  * ecx = HD base: 1=IDE0, 2=IDE1, 3=IDE2, 4=IDE3

Returned value:

  * eax = 0

Remarks:

  * Any application at any time can change the base.

  * Do not change base, when any application works with hard disk.

    If you do not want system bugs.

  * To get HD base use subfunction 7 of function 26.

  * It is also necessary to define used partition of hard disk by

    subfunction 8.

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========= Function 21, subfunction 8 - set used HD partition. ========

======================================================================

The HD partition defines partition of the hard disk to write with

usage of obsolete syntax /HD and obsolete function 58;

at usage of functions 58 and 70 and modern syntax /HD0,/HD1,/HD2,/HD3

base and partition are set automatically.

Parameters:

  * eax = 21 - function number

  * ebx = 8 - subfunction number

  * ecx = HD partition (beginning from 1)

Return value:

  * eax = 0

Remarks:

  * Any application at any time can change partition.

  * Do not change partition when any application works with hard disk.

    If you do not want system bugs.

  * To get used partition use subfunction 8 of function 26.

  * There is no correctness checks.

  * To get the number of partitions of a hard disk use

    subfunction 11 of function 18.

  * It is also necessary to define used HD base by subfunction 7.

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============== Function 26, subfunction 7 - get HD base. =============

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The HD base defines hard disk to write with usage of obsolete

syntax /HD in obsolete function 58; at usage of modern syntax

/HD0,/HD1,/HD2,/HD3 base is set automatically.

Parameters:

  * eax = 26 - function number

  * ebx = 7 - subfunction number

Returned value:

  * eax = HD base: 1=IDE0, 2=IDE1, 3=IDE2, 4=IDE3

Remarks:

  * Any application in any time can change HD base.

  * To set base use subfunction 7 of function 21.

  * To get used partition of hard disk use subfunction 8.

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========= Function 26, subfunction 8 - get used HD partition. ========

======================================================================

The HD partition defines partition of the hard disk to write with

usage of obsolete syntax /HD in obsolete function 58;

at usage of functions 58 and 70 and modern syntax /HD0,/HD1,/HD2,/HD3

base and partition are set automatically.

Parameters:

  * eax = 26 - function number

  * ebx = 8 - subfunction number

Returned value:

  * eax = HD partition (beginning from 1)

Remarks:

  * Any application in any time can change partition.

  * To set partition use subfunction 8 of function 21.

  * To get number of partitions on a hard disk use

    subfunction 11 of function 18.

  * To get base of used hard disk, use subfunction 7.

    which the fields of intermediate buffer and file name are filled

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================ Function 58 - work with file system. ================

======================================================================

Parameters:

  * eax = 58

  * ebx = pointer to the information structure

Returned value:

  * eax = 0 - success; otherwise file system error code

  * some subfunctions return value in other registers too

General format of the information structure:

  * +0: dword: subfunction number

  * +4: dword: number of block

  * +8: dword: size

  * +12 = +0xC: dword: pointer to data

  * +16 = +0x10: dword: pointer to a memory for system operations

    (4096 bytes)

  * +20 = +0x14: n db: ASCIIZ-string with the file name

Specifications - in documentation on the appropriate subfunction.

Filename is case-insensitive for latin letters, russian letters

must be capital.

Format of filename:

/base/number/dir1/dir2/.../dirn/file,

where /base/number identifies device, on which file is located:

one of

  * /RD/1 = /RAMDISK/1 to access ramdisk

  * /FD/1 = /FLOPPYDISK/1 to access first floppy drive,

    /FD/2 = /FLOPPYDISK/2 to access second one

  * /HD/x = /HARDDISK/x - obsolete variant of access to hard disk

    (in this case base is defined by subfunction 7 of function 21),

    x - partition number (beginning from 1)

  * /HD0/x, /HD1/x, /HD2/x, /HD3/x to access accordingly to devices

    IDE0 (Primary Master), IDE1 (Primary Slave),

    IDE2 (Secondary Master), IDE3 (Secondary Slave);

    x - partition number on the selected hard drive, varies from 1

    to 255 (on each hard drive the indexing starts from 1)

Remarks:

  * In the first two cases it is also possible to use FIRST

    instead of 1, SECOND instead of 2, but it is not recommended

    for convenience of transition to the future extensions.

  * Limitation n<=39 is imposed.

  * Names of folders and file dir1,...,dirn,file must have the

    format 8.3: name no more than 8 characters, dot, extension no

    more than 3 characters. Trailing spaces are ignored, no other

    spaces is allowed. If name occupies equally 8 characters,

    dot may be omitted (though it is not recommended to use this

    feature for convenience of transition to the future extensions).

  * This function does not support folders on ramdisk.

Examples:

  * '/RAMDISK/FIRST/KERNEL.ASM',0

    '/rd/1/kernel.asm',0

  * '/HD0/1/kernel.asm',0

  * '/hd0/1/menuet/pics/tanzania.bmp',0

Existing subfunctions:

  * subfunction 0 - read file/folder

  * subfunction 8 - LBA-read from device

  * subfunction 15 - get file system information

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=========== Function 58, subfunction 0 - read file/folder. ===========

======================================================================

Parameters:

  * eax = 58

  * ebx = pointer to the information structure

Format of the information structure:

  * +0: dword: 0 = subfunction number

  * +4: dword: first block to read (beginning from 0)

  * +8: dword: amount of blocks to read

  * +12 = +0xC: dword: pointer to buffer for data

  * +16 = +0x10: dword: pointer to buffer for system operations

    (4096 bytes)

  * +20 = +0x14: ASCIIZ-name of file, the rules of names forming are

    given in the general description

Returned value:

  * eax = 0 - success, otherwise file system error code

  * ebx = file size (in bytes) or -1=0xffffffff, if file was not found

Remarks:

  * Block size is 512 bytes.

  * This function is obsolete, for reading files use subfunction 0

    of function 70, for reading folders - subfunction 1 of

    function 70.

  * Function can read contents of a folder. Only FAT file system is

    supported. The format of FAT-folder is described

    in any FAT documentation.

  * Size of a folder is determined by size of FAT clusters chain.

  * If file was ended before last requested block was read,

    the function will read as many as it can, and after that return

    eax=6 (EOF).

  * Function can read root folders /rd/1,/fd/x,/hd[n]/x, but

    in the first two cases the current implementation does not follow

    to the declared rules:

    for /rd/1:

    * if one want to read 0 blocks, function considers,

      that he requested 1;

    * if one requests more than 14 blocks or starting block is

      not less than 14, function returns eax=5 (not found) and ebx=-1;

    * size of ramdisk root folder is 14 blocks,

      0x1C00=7168 bytes; but function returns ebx=0

      (except of the case of previous item);

    * strangely enough, it is possible to read 14th block (which

      generally contains a garbage - I remind, the indexing begins

      from 0);

    * if some block with the number not less than 14 was requested,

      function returns eax=6(EOF); otherwise eax=0.

    For /fd/x:

    * if the start block is not less than 14, function returns

      eax=5 (not found) and ebx=0;

    * note that format of FAT12 allows floppies with the root size

      more or less than 14 blocks;

    * check for length is not performed;

    * if data was successful read, function returns

      eax=0,ebx=0; otherwise eax=10 (access denied), ebx=-1.

  * The function handles reading of special folders /,/rd,/fd,/hd[n];

    but the result does not correspond to expected (on operations with

    normal files/folders), does not follow the declared rules,

    may be changed in future versions of the kernel and consequently

    is not described. To obtain the information about the equipment

    use subfunction 11 of function 18 or

    read corresponding folder with subfunction 1 of function 70.

======================================================================

========= Function 58, subfunction 8 - LBA-read from device. =========

======================================================================

Parameters:

  * eax = 58 - function number

  * ebx = pointer to the information structure

Format of the information structure:

  * +0: dword: 8 = subfunction number

  * +4: dword: number of block to read (beginning from 0)

  * +8: dword: ignored (set to 1)

  * +12 = +0xC: dword: pointer to buffer for data (512 bytes)

  * +16 = +0x10: dword: pointer to buffer for system operations

    (4096 bytes)

  * +20 = +0x14: ASCIIZ-name of device: case-insensitive, one of

    /rd/1 = /RamDisk/1, /hd/n = /HardDisk/n,

    1<=n<=4 - number of device: 1=IDE0, ..., 4=IDE3.

    Instead of digits it is allowed, though not recommended for

    convenience of transition to future extensions, to use

    'first','second','third','fourth'.

Returned value:

  * for device name /hd/xxx, where xxx is not in the list above:

    * eax = ebx = 1

  * for invalid device name (except for the previous case):

    * eax = 5

    * ebx does not change

  * if LBA-access is disabled by subfunction 11 of function 21:

    * eax = 2

    * ebx destroyed

  * for ramdisk: attempt to read block outside ramdisk

    (18*2*80 blocks) results in

    * eax = 3

    * ebx = 0

  * for successful read:

    * eax = ebx = 0

Remarks:

  * Block size is 512 bytes; function reads one block.

  * Do not depend on returned value, it can be changed

    in future versions.

  * Function requires that LBA-access to devices is enabled by

    subfunction 11 of function 21. To check this one can use

    subfunction 11 of function 26.

  * LBA-read of floppy is not supported.

  * Function reads data on physical hard drive; if for any reason

    data of the concrete partition are required, application must

    define starting sector of this partition (either directly

    through MBR, or from the full structure returned by

    subfunction 11 of function 18).

  * Function does not check error code of hard disk, so request of

    nonexisting sector reads something (most probably it will be

    zeroes, but this is defined by device) and this is considered

    as success (eax=0).

======================================================================

==== Function 58, subfunction 15 - get information on file system. ===

======================================================================

Parameters:

  * eax = 58 - function number

  * ebx = pointer to the information structure

Format of the information structure:

  * +0: dword: 15 = subfunction number

  * +4: dword: ignored

  * +8: dword: ignored

  * +12 = +0xC: dword: ignored

  * +16 = +0x10: dword: ignored

  * +20 = +0x14: (only second character is checked)

    /rd=/RAMDISK or /hd=/HARDDISK

Returned value:

  * if the second character does not belong to set {'r','R','h','H'}:

    * eax = 3

    * ebx = ecx = dword [fileinfo] = 0

  * for ramdisk:

    * eax = 0 (success)

    * ebx = total number of clusters = 2847

    * ecx = number of free clusters

    * dword [fileinfo] = cluster size = 512

  * for hard disk: base and partition are defined by subfunctions

    7 and 8 of function 21:

    * eax = 0 (success)

    * ebx = total number of clusters

    * ecx = number of free clusters

    * dword [fileinfo] = cluster size (in bytes)

Remarks:

  * Be not surprised to strange layout of 4th returned parameter

    - when this code was writing, at system calls application got

    only registers eax,ebx,ecx (from pushad-structure transmitted

    as argument to the system function). Now it is corrected, so,

    probably, it is meaningful to return cluster size in edx, while

    this function is not used yet.

  * There exists also subfunction 11 of function 18,

    which returns information on file system. From the full table

    of disk subsystem it is possible to deduce cluster size (there

    it is stored in sectors) and total number of clusters

    for hard disks.