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DISKLABEL(9)             BSD Kernel Developer's Manual            DISKLABEL(9)

NAME
     disklabel, readdisklabel, writedisklabel, setdisklabel,
     bounds_check_with_label -- disk label management routines

SYNOPSIS
     #include <&lt;sys/param.h>&gt;
     #include <&lt;sys/disklabel.h>&gt;

     int
     readdisklabel(dev_t dev, void (*strat)(struct buf *),
         struct disklabel *lp, int spoofonly);

     int
     writedisklabel(dev_t dev, void (*strat)(struct buf *),
         struct disklabel *lp);

     int
     setdisklabel(struct disklabel *olp, struct disklabel *nlp,
         u_int openmask);

     int
     bounds_check_with_label(struct buf *bp, struct disklabel *lp);

DESCRIPTION
     This collection of routines provides a disklabel management interface to
     kernel device drivers.  These routines are classified as machine- or
     architecture-dependent because of restrictions imposed by the machine
     architecture and boot-strapping code on the location of the label, or
     because cooperation with other operating systems requires specialized
     conversion code.

     readdisklabel() attempts to read a disklabel from the device identified
     by dev, using the device strategy routine passed in strat.  Note that a
     buffer structure is required to pass to the strategy routine; it needs to
     be acquired and parametrized for the intended I/O operation, and disposed
     of when the operation has completed.  Some fields in the disklabel passed
     in lp may be pre-initialized by the caller in order to meet device driver
     requirements for the I/O operation initiated to get to the disklabel data
     on the medium.  In particular, the field ``d_secsize'', if non-zero, is
     used by readdisklabel() to get an appropriately sized buffer to pass to
     the device strategy routine.  Unspecified fields in lp should be set to
     zero.  If the medium does not contain a native disklabel that can be read
     in directly or spoofonly argument is a true value, If a disk label is
     found or can be constructed a value of 0 is returned.  Otherwise the
     value of the I/O errno encountered is returned.

     writedisklabel() stores disk label information contained in the disk
     label structure given by lp on the device identified by dev.  Like
     readdisklabel(), it acquires and sets up an I/O buffer to pass to the
     strategy routine strat.  writedisklabel() returns 0 on success and EINVAL
     if the disk label specifies invalid or unconvertible values.  Otherwise,
     any error condition reported by the device strategy routine in the buf-
     fer's ``b_error'' field is returned.

     setdisklabel() checks a proposed new disk label passed in nlp for some
     amount of basic sanity.  This includes a check on attempts to change the
     location, or reduce the size, of an existing disk partition that is cur-
     rently in use by the system.  The current disposition of the disk parti-
     tions is made available through olp and openmask, which provide, respec-
     tively, the existing disk label and a bit mask identifying the partitions
     that are currently in use.  Failure to pass on ``basic sanity'', results
     in a EINVAL return value, while a vetoed update of the partition layout
     is signalled by a EBUSY return value.  Otherwise, 0 is returned.

     bounds_check_with_label() is used to check whether a device transfer
     described by bp to the device identified by dev, is properly contained
     within a disk partition of the disk with label lp.  If this check fails,
     bounds_check_with_label() sets the buffer's ``b_error'' field to EINVAL
     and sets the B_ERROR flag in ``b_flags''.  A value of -1 is returned if
     any of the bound checks failed, a null transfer was attempted, or trans-
     fer was attempted exactly at the end of the disk partition.  Otherwise
     the value of 0 is returned.

SEE ALSO
     disklabel(5), disklabel(8), fdisk(8)

BSD                              June 4, 2013                              BSD