172 lines
3.1 KiB
Text
172 lines
3.1 KiB
Text
.TH DISK 2
|
|
.SH NAME
|
|
opendisk, Disk \- generic disk device interface
|
|
.SH SYNOPSIS
|
|
.nf
|
|
.ft L
|
|
#include <u.h>
|
|
#include <libc.h>
|
|
#include <disk.h>
|
|
.ft
|
|
.PP
|
|
.ft L
|
|
typedef struct Disk {
|
|
char *prefix;
|
|
char part[NAMELEN];
|
|
int fd, wfd, ctlfd, rdonly;
|
|
int type;
|
|
vlong secs, secsize, size, offset;
|
|
int c, h, s;
|
|
} Disk;
|
|
.ft
|
|
.PP
|
|
.B
|
|
Disk* opendisk(char *file, int rdonly, int noctl)
|
|
.SH DESCRIPTION
|
|
These routines provide a simple way to gather
|
|
and use information about
|
|
.IR floppy (3)
|
|
and
|
|
.IR sd (3)
|
|
disks and disk partitions,
|
|
as well as plain files.
|
|
.PP
|
|
.I Opendisk
|
|
opens
|
|
.I file
|
|
for reading and stores the file descriptor in
|
|
the
|
|
.B fd
|
|
field of the
|
|
.B Disk
|
|
structure.
|
|
If
|
|
.I rdonly
|
|
is not set,
|
|
.I opendisk
|
|
also opens
|
|
.I file
|
|
for writing and stores that file descriptor in
|
|
.BR wfd .
|
|
The two file descriptors are kept separate to
|
|
help prevent accidents.
|
|
.PP
|
|
If
|
|
.I noctl
|
|
is not set,
|
|
.I opendisk
|
|
looks for a
|
|
.B ctl
|
|
file in the same directory as the
|
|
disk file;
|
|
if it finds one, it declares
|
|
the disk to be
|
|
an
|
|
.I sd
|
|
device,
|
|
setting the
|
|
.B type
|
|
field in the
|
|
.B Disk
|
|
structure
|
|
to
|
|
.BR Tsd .
|
|
If the passed
|
|
.I file
|
|
is named
|
|
.BI fd n disk \fR,
|
|
it looks for a file
|
|
.BI fd n ctl \fR,
|
|
and if it finds that,
|
|
declares the disk to be
|
|
a floppy disk, of type
|
|
.BR Tfloppy .
|
|
If either
|
|
control
|
|
file is found, it is opened for reading
|
|
and writing, and the resulting file descriptor
|
|
is saved as
|
|
.BR ctlfd .
|
|
Otherwise the returned disk
|
|
has type
|
|
.BR Tfile .
|
|
.PP
|
|
.I Opendisk
|
|
then stats the file and stores its length in
|
|
.BR size .
|
|
If the disk is an
|
|
.I sd
|
|
partition,
|
|
.I opendisk
|
|
reads the sector size from the
|
|
control
|
|
file and stores it in
|
|
.BR secsize ;
|
|
otherwise the sector size is assumed to be 512,
|
|
as is the case for floppy disks.
|
|
.I Opendisk
|
|
then stores the disk size measured in sectors in
|
|
.BR secs .
|
|
.PP
|
|
If the disk is an
|
|
.I sd
|
|
partition,
|
|
.I opendisk
|
|
parses the
|
|
control
|
|
file to find the partition's offset
|
|
within its disk;
|
|
otherwise it sets
|
|
.B offset
|
|
to zero.
|
|
If the disk is an ATA disk,
|
|
.I opendisk
|
|
reads
|
|
the disk geometry (number of cylinders, heads, and sectors)
|
|
from the
|
|
.B geometry
|
|
line in the
|
|
.I sd
|
|
control file;
|
|
otherwise it sets these to zero as well.
|
|
.B Name
|
|
is initialized with the base name of
|
|
the disk partition, and is useful for forming messages to the
|
|
.I sd
|
|
control file.
|
|
.B Prefix
|
|
is set to the passed filename without
|
|
the
|
|
.B name
|
|
suffix.
|
|
.PP
|
|
The IBM PC BIOS interface allocates
|
|
10 bits for the number of cylinders, 8 for
|
|
the number of heads, and 6 for the number of sectors per track.
|
|
Disk geometries are not quite so simple
|
|
anymore, but to keep the interface useful,
|
|
modern disks and BIOSes present geometries
|
|
that still fit within these constraints.
|
|
These numbers are still used when partitioning
|
|
and formatting disks.
|
|
.I Opendisk
|
|
employs a number of heuristics to discover this
|
|
supposed geometry and store it in the
|
|
.BR c ,
|
|
.BR h ,
|
|
and
|
|
.B s
|
|
fields.
|
|
Disk offsets in partition tables and
|
|
in FAT descriptors are stored in a form
|
|
dependent upon these numbers, so
|
|
.I opendisk
|
|
works hard to report numbers that
|
|
agree with those used by other operating
|
|
systems; the numbers bear little or no resemblance
|
|
to reality.
|
|
.SH SOURCE
|
|
.B /sys/src/libdisk/disk.c
|
|
.SH SEE ALSO
|
|
.IR floppy (3),
|
|
.IR sd (3)
|