DC(4) GENIX Programmer's Manual DC(4)
NAME
dc - SYS16 disk driver for ANSI interface disks
DESCRIPTION
Files with minor device numbers 0 through 7 refer to various por-
tions of drive 0; minor devices 8 through 15 refer to drive 1, etc.
The standard device names begin with "dc" followed by the drive
number and then a letter a-h for partitions 0-7 respectively. The
character `?' stands here for a drive number in the range 0-7.
It is unwise for all of these files to be present in one installa-
tion, because there is overlap in addresses and protection becomes a
sticky matter. The dc?a partition is normally used for the root
file system, the dc?b partition as a paging area, the dc?c partition
for pack-pack copying (it maps the entire disk). On large disks,
the dc?h partition is inserted prior to the dc?d or dc?g partition;
the dc?g partition then maps the remainder of the pack.
The block files access the disk via the system's normal buffering
mechanism and may be read and written without regard to physical
disk records. A `raw' interface, which provides for direct
transmission between the disk and the user's read or write buffer,
is also available. A single read or write call results in exactly
one I/O operation and therefore raw I/O is considerably more effi-
cient when many words are transmitted. The names of the raw files
conventionally begin with an extra `r.'
In raw I/O counts must be a multiple of 512 bytes (one page), and
the buffer address must be a multiple on 512 (i.e., be page-
aligned). This is a restriction imposed by the disk controller.
Attempts to perform I/O without following these restrictions results
in an EIO error. Likewise lseek(2) calls should specify a multiple
of 512 bytes.
DISK SUPPORT
This driver supports any ANSI interface drive that contains a valid
header (as described by disk(5)) on physical sector 0. The drive
header is read off each pack and used to initialize the driver with
the disk configuration information, and the origin and size (in sec-
tors) of the psuedo-disks. The origin and size of the psuedo-disks
may be changed with mkpt(8).
FILES
/dev/dc[0-7][a-h] block files
/dev/rdc[0-7][a-h] raw files
/usr/include/sys/disk.h disk header layout
DIAGNOSTICS
%s disk %s error: unit %d sector %d status %x retries %d. This mes-
sage appears on the console when a disk error occurs. The status
indicates the reason for the error. The dcerr(8) program can be
used to decode the status.
Printed 11/16/83 1
DC(4) GENIX Programmer's Manual DC(4)
SEE ALSO
disk(5), mkpt(8)
BUGS
The page-alignment restriction for raw I/O should not exist.
Bad block forwarding is not yet supported.
Printed 11/16/83 2