DIO_FUNCTION

Section: Misc. Reference Manual Pages (2L)
Updated: Data Logic Limited
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NAME

dio_functions - MSDOS Raw Disk/Memory I/O Functions

SYNOPSIS

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ms_dio.h>

int dio_access (path, amode)
int dio_chmod (path, mode)
int dio_close (fildes)
int dio_creat (path, mode)
int dio_dup (fildes)
int dio_isatty (fildes)
long dio_lseek (fildes, offset, whence)
int dio_open (path, oflag [ , mode ] )
int dio_read (fildes, buf, nbyte)
int dio_stat (path, statb)
int dio_fstat (fildes, statb)
int dio_write (fildes, buf, nbyte)
long dio_tell (fildes)

char *path;
char *buf;
int amode;
int mode;
int fildes;
int whence;
int oflag;
long offset;
unsigned int nbyte;
struct stat *statb;

DESCRIPTION

These functions provide replacements for the standard MS-DOS library function of similar name. The object of these functions is to allow the user to access either the files, or raw disks or memory using standard library calls, in a similar manner to UNIX where files or devices can be accessed using the standard library functions. A set of macros is provided in the include file ms_dio.h which maps the standard library functions onto one of these functions. If the file name or file descriptor refers to a normal MSDOS file, the standard library function is invoked to perform the required function. Otherwise, the appropriate action is taken by these replacement functions. The functionality of the libraries is described on the appropriate manual pages for the standard function.

These libraries recognise three devices - hard disks, floppy disks or memory and these are accessed using the following file names:

/dev/fdn: This device allows the user to access a floppy disk. The digit n gives the drive number (from 0 to 9). The topological information for this device (heads, tracks, sectors) is obtained from MS-DOS. The open function then checks to see what type of disk is loaded. The following disks are recognised (8, 9 or 15 sectors, 1 or 2 heads, double or single density). The drive density is selected when necessary by attempting to read sector 0 from the disk.
/dev/hdxy: This device allows the user to access a hard disk. The first digit x gives the drive number (from 0 to 9) and the second digit y gives the partition number on the disk (from 0 to 9). Partition zero refers to the whole disk. Note that the open function sorts the partition table before deciding which partition is referred to. All topological information for this device (heads, tracks, sectors) is obtained from MS-DOS.
/dev/mem: This device allows the user to access memory from location 0 to location 0xFFFFF.

The libraries use/return file descriptors in the range 30000 to 32767 and use this as a check to see if they are processing one of the special files mentioned above. This value can be changed by modifying the value of MS_MODIFIER in the library source.

Note: File descriptors for these special devices cannot be passed via exec or spawn to new or child processes.

RETURN VALUE

See standard library functions. If an error occurs, errno is set to EIO if the error occurs when reading or writing the device.