creatediskbyname.3x

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)creatediskbyname.3x	6.2	8/30/89
.TH creatediskbyname 3x
.SH Name
creatediskbyname \- get the disk description associated with a file name
.SH Syntax
.nf
.B #include <disktab.h>
.PP
.B struct disktab *
.B creatediskbyname(\fIname\fP)
.B char *\fIname\fP;
.fi
.SH Description
.NXR "creatediskbyname subroutine"
.NXR "disk" "getting description"
The
.PN creatediskbyname
subroutine
takes the name of the character device special file representing a 
disk device (for example, 
.PN /dev/rra0a) 
and returns a structure pointer
describing its geometry information and the default
disk partition tables.  It obtains this information by
polling the controlling disk device driver.  
The
.PN creatediskbyname
subroutine returns information only for MSCP and SCSI disks.
.PP
The 
.PN <disktab.h> 
file has the following form:
.EX 0
#define DISKTAB        "/etc/disktab"

struct  disktab {
      char   *d_name;          /* drive name */
      char   *d_type;          /* drive type */
      int    d_secsize;        /* sector size in bytes */
      int    d_ntracks;        /* # tracks/cylinder */
      int    d_nsectors;       /* # sectors/track */
      int    d_ncylinders;     /* # cylinders */
      int    d_rpm;            /* revolutions/minute */
      struct partition {
              int     p_size;   /* #sectors in partition */
              short   p_bsize;  /* block size in bytes */
              short   p_fsize;  /* frag size in bytes */
        } d_partitions[8];
};

struct  disktab *getdiskbyname();
struct  disktab *creatediskbyname();
.EE
.SH Diagnostics
Successful completion of the 
.PN creatediskbyname
subroutine returns a pointer to a valid disktab structure.  Failure of
this subroutine returns a null pointer.  The subroutine
fails if it cannot obtain the necessary information from the device
driver or disktab file.
.PP
A check is done to ensure that the disktab file exists and is readable.
This check ensures that the subroutine is not being called
because the disktab file was accidentally removed.  If there is no 
disktab file, the subroutine fails.
.PP
The 
.PN creatediskbyname
subroutine also fails if it cannot determine disk geometry
attributes by polling the driver.  This can occur if the disk is not
an MSCP or SCSI disk.  In some cases where the disk consists
of removable media and the media is not loaded, the 
driver will be unable to determine disk attributes.
.SH Restrictions
The
.PN creatediskbyname
subroutine returns information only for MSCP and SCSI disks.
.SH See Also
getdiskbyname(3x), ra(4), rz(4), disktab(5)