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Diffstat (limited to 'man/man3/disk.3')
-rw-r--r-- | man/man3/disk.3 | 177 |
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diff --git a/man/man3/disk.3 b/man/man3/disk.3 new file mode 100644 index 00000000..30e4440a --- /dev/null +++ b/man/man3/disk.3 @@ -0,0 +1,177 @@ +.TH DISK 3 +.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 +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 /usr/local/plan9/src/libdisk/disk.c +.SH SEE ALSO +Plan 9's +\fIfloppy\fR(3) and \fIsd\fR(3) +.SH BUGS +Disks on Unix systems do not present the interface +that +.I opendisk +expects, so +.I opendisk +will give them type +.BR Tfile . |