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ioctl (DOS)
===========

The DOSish version of `ioctl' performs an interrupt 0x21, function
0x44. It takes care of supplying transfer buffers in low address
regions, if they are needed. For an exhaustive description of the
various commands and subcommands, see Ralph Browns interrupt list.

It is highly recommended to use only the DOS_* functions listed in
`sys/ioctl.h'.

Syntax
------

ioctl(fd, cmd, ... );

     #include <sys/ioctl.h>
     int main(int argc, char **argv){
        char buf[6];
        short *s;
     
        open(fd,"EMMQXXX0",O_RDONLY);
        mybuf[0] = '\0';
        s = mybuf;
        ioctl(fd,DOS_SNDDATA,6, (int) &mybuf);
        if(*s ==0x25 )printf("EMM386 >= 4.45\n");
        mybuf[0]='\x02';
        ioctl(fd,DOS_SNDDATA,2,(int )&mybuf);
        printf("EMM Version %d.%d\n",(int )mybuf[0],(int) mybuf[1]);
        close(fd);
     }

Description
-----------

The parameter `fd' must refer to a file descriptor for character device
functions, or the number of a block device (usually current=0, A:=1,
...).

The following constants can be used for the `cmd' parameter:
`DOS_GETDEVDATA'
     Get device information. Returns the device information word from
     `DX'.

`DOS_SETDEVDATA'
     Set device information. Returns the new device information word
     form `DX' or -1

`DOS_RCVDATA'
     Read from character device control channel. After `cmd' must
     follow the number of requested bytes to read and a pointer to a
     buffer. Returns the number of bytes actually read or -1 on error.

`DOS_SNDDATA'
     Write to character device control channel. After `cmd' must follow
     the number of bytes to write and a pointer to a buffer holding the
     data.  Returns the number of bytes actually written.

`DOS_RCVCTLDATA'
     Read from block device control channel. See `DOS_RCVDATA'.

`DOS_SNDCTLDATA'
     Write to block device control channel. See `DOS_SNDDATA'.

`DOS_CHKINSTAT'
     Check the input status of a file. Returns 0 if not ready of at
     EOF, `0xff' if file is ready.

`DOS_CHKOUTSTAT'
     Check the output status of a file. Returns 0 if not ready of at
     EOF, `0xff' if file is ready.

`DOS_ISCHANGEABLE'
     Check if a block device is changeable. Returns 0 for removable or
     1 for fixed.

`DOS_ISREDIRBLK'
     Check if a block device is remote o local.

`DOS_ISREDIRHND'
     Check if a file handle refers to a local or remote device.

`DOS_SETRETRY'
     Set the sharing retry count. the first extra parameter specifies
     the pause between retries, the second number of retries.

`DOS_GENCHARREQ'
     Generic character device request.

`DOS_GENBLKREQ'
     Generic block device request.

`DOS_GLDRVMAP'
     Get logical drive map.

`DOS_SLDRVMAP'
     Set logical drive map.

`DOS_QGIOCTLCAPH'
     Query generic ioctl capability (handle). Test if a handle supports
     ioctl functions beyond those in the standard DOS 3.2 set.

`DOS_QGIOCTLCAPD'
     Query generic ioctl capability (drive). Test if a drive supports
     ioctl functions beyond those in the standard DOS 3.2 set.

If your specific device driver requires different commands, they must
be or'ed together with the flags listed in `ioctl.h' to tell the drive
about transfer buffers and what to return.

Return Value
------------

See description above.

Device information word
-----------------------

The bits of the device information word have the following meaning:\\
Character device:
     14  Device driver can process IOCTL request

     13  output until busy supported

     11  driver supports OPEN/CLOSE calls

     7   set (indicates device)

     6   EOF on input

     5   raw (binary) mode

     4   device is special (uses INT 29)

     3   clock device

     2   NUL device

     1   standard output

     0   standard input

Disk file:
     15  file is remote (DOS 3.0+)

     14  don't set file date/time on closing (DOS 3.0+)

     11  media not removable

     8   (DOS 4 only) generate INT 24 if no disk space on write or read
     past end of file

     7   clear (indicates file)

     6   file has not been written

     5-0 drive number (0 = A:)