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+.\" sd.4
+.\" Copyright 1992 Rickard E. Faith (faith@cs.unc.edu)
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH sd 4 2023-02-05 "Linux man-pages 6.05.01"
+.SH NAME
+sd \- driver for SCSI disk drives
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/hdreg.h>        " "/* for HDIO_GETGEO */"
+.BR "#include <linux/fs.h>           " "/* for BLKGETSIZE and BLKRRPART */"
+.fi
+.SH CONFIGURATION
+The block device name has the following form:
+.BI sd lp,
+where
+.I l
+is a letter denoting the physical drive, and
+.I p
+is a number denoting the partition on that physical drive.
+Often, the partition number,
+.IR p ,
+will be left off when the device corresponds to the whole drive.
+.PP
+SCSI disks have a major device number of 8, and a minor device number of
+the form (16 *
+.IR drive_number ") + " partition_number ,
+where
+.I drive_number
+is the number of the physical drive in order of detection, and
+.I partition_number
+is as follows:
+.IP \[bu] 3
+partition 0 is the whole drive
+.IP \[bu]
+partitions 1\[en]4 are the DOS "primary" partitions
+.IP \[bu]
+partitions 5\[en]8 are the DOS "extended" (or "logical") partitions
+.PP
+For example,
+.I /dev/sda
+will have major 8, minor 0, and will refer to all of the first SCSI drive
+in the system; and
+.I /dev/sdb3
+will have major 8, minor 19, and will refer to the third DOS "primary"
+partition on the second SCSI drive in the system.
+.PP
+At this time, only block devices are provided.
+Raw devices have not yet been implemented.
+.SH DESCRIPTION
+The following
+.IR ioctl s
+are provided:
+.TP
+.B HDIO_GETGEO
+Returns the BIOS disk parameters in the following structure:
+.PP
+.in +4n
+.EX
+struct hd_geometry {
+    unsigned char  heads;
+    unsigned char  sectors;
+    unsigned short cylinders;
+    unsigned long  start;
+};
+.EE
+.in
+.IP
+A pointer to this structure is passed as the
+.BR ioctl (2)
+parameter.
+.IP
+The information returned in the parameter is the disk geometry of the drive
+.I "as understood by DOS!"
+This geometry is
+.I not
+the physical geometry of the drive.
+It is used when constructing the
+drive's partition table, however, and is needed for convenient operation
+of
+.BR fdisk (1),
+.BR efdisk (1),
+and
+.BR lilo (1).
+If the geometry information is not available, zero will be returned for all
+of the parameters.
+.TP
+.B BLKGETSIZE
+Returns the device size in sectors.
+The
+.BR ioctl (2)
+parameter should be a pointer to a
+.IR long .
+.TP
+.B BLKRRPART
+Forces a reread of the SCSI disk partition tables.
+No parameter is needed.
+.IP
+The SCSI
+.BR ioctl (2)
+operations are also supported.
+If the
+.BR ioctl (2)
+parameter is required, and it is NULL, then
+.BR ioctl (2)
+fails with the error
+.BR EINVAL .
+.SH FILES
+.TP
+.I /dev/sd[a\-h]
+the whole device
+.TP
+.I /dev/sd[a\-h][0\-8]
+individual block partitions
+.\".SH SEE ALSO
+.\".BR scsi (4)