DISKLABEL(9)                 OpenBSD Kernel Manual                DISKLABEL(9)

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

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

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

     int
     setdisklabel(struct disklabel *olp, struct disklabel *nlp,
             u_long openmask, struct cpu_disklabel *osdep);

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

DESCRIPTION
     This collection of routines provides a disklabel management interface to
     kernel device drivers.  These routines are classified as machine- or ar-
     chitecture-dependent because of restrictions imposed by the machine ar-
     chitecture and boot-strapping code on the location of the label, or be-
     cause cooperation with other operating systems requires specialized con-
     version 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 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 diskla-
     bel 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,
     readdisklabel() may resort to constructing a label from other machine-de-
     pendent information using the provided buffer passed in the osdep argu-
     ment.  If a disk label can not be found or constructed, a string contain-
     ing an approximated description of the failure mode is returned.  Other-
     wise the NULL string is returned.

     writedisklabel() stores disk label information contained in the disk la-
     bel 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() may elect to do a machine-depen-
     dent conversion of the native disk label structure (using the buffer
     pointed at by osdep), to store the disk label onto the medium in a format
     complying with architectural contraints.  writedisklabel() returns 0 on
     success and EINVAL if the disk label specifies invalid or unconvertable
     values.  Otherwise, any error condition reported by the device strategy
     routine in the buffer'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 signaled by a EBUSY return value.  Otherwise, 0 is returned.

     bounds_check_with_label() is used to check whether a device transfer de-
     scribed 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''. If the argument wlabel is zero,
     and the transfer is a write operation, a check is done if the transfer
     would overwrite (a portion of) the disklabel area on the medium.  If that
     is the case, EROFS is set in ``b_error'' and the B_ERROR flag is set in
     ``b_flags''. Note that wlabel should be set to a non-zero value if the
     intended operation is expected to install or update the disk label.  Pro-
     grams that intend to do so using the raw device interface should notify
     the driver by using a DIOCWLABEL ioctl function.  Zero value is returned
     if any of the bound checks failed or transfer was attempted exactly at
     the end of disk partition.  Otherwise the value of 1 is returned.

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

OpenBSD 2.8                    December 26, 1996                             2
