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       sd - driver for SCSI disk drives


       #include <linux/hdreg.h>        /* for HDIO_GETGEO */
       #include <linux/fs.h>           /* for BLKGETSIZE and BLKRRPART */


       The  block  device  name  has  the  following form: sdlp, where l is a letter denoting the
       physical drive, and p is a number denoting the partition on that physical  drive.   Often,
       the partition number, p, will be left off when the device corresponds to the whole drive.

       SCSI  disks  have  a major device number of 8, and a minor device number of the form (16 *
       drive_number) + partition_number, where drive_number is the number of the  physical  drive
       in order of detection, and partition_number is as follows:

       +3     partition 0 is the whole drive

              partitions 1–4 are the DOS "primary" partitions

              partitions 5–8 are the DOS "extended" (or "logical") partitions

       For  example, /dev/sda will have major 8, minor 0, and will refer to all of the first SCSI
       drive in the system; and /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.

       At this time, only block devices are provided.  Raw devices have not yet been implemented.


       The following ioctls are provided:

              Returns the BIOS disk parameters in the following structure:

           struct hd_geometry {
               unsigned char  heads;
               unsigned char  sectors;
               unsigned short cylinders;
               unsigned long  start;

              A pointer to this structure is passed as the ioctl(2) parameter.

              The  information  returned  in  the  parameter is the disk geometry of the drive as
              understood by DOS!  This geometry is 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  fdisk(1),  efdisk(1),  and  lilo(1).   If  the  geometry
              information is not available, zero will be returned for all of the parameters.

              Returns  the device size in sectors.  The ioctl(2) parameter should be a pointer to
              a long.

              Forces a reread of the SCSI disk partition tables.  No parameter is needed.

              The SCSI ioctl(2) operations are also supported.   If  the  ioctl(2)  parameter  is
              required, and it is NULL, then ioctl(2) fails with the error EINVAL.


              the whole device

              individual block partitions


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