DISKLABEL(9)           NetBSD Kernel Developer's 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 *clp);

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

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

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

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 parameterized for the intended I/O operation, and dis-
     posed 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 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, readdisklabel() may resort to constructing a label
     from other machine-dependent information using the provided buffer passed
     in the clp argument.  If a disk label can not be found or constructed, a
     string containing an approximated description of the failure mode is
     returned.  Otherwise the NULL string 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() may elect to do a machine-
     dependent conversion of the native disk label structure (using the buffer
     pointed at by clp), to store the disk label onto the medium in a format
     complying with architectural constraints.  writedisklabel() returns 0 on
     success and EINVAL if the disk label specifies invalid or inconvertible
     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
     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,
     sets the B_ERROR flag in ``b_flags'', and returns -1.  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'', the B_ERROR
     flag is set in ``b_flags'', and -1 is returned.  Note that wlabel should
     be set to a non-zero value if the intended operation is expected to
     install or update the disk label.  Programs that intend to do so using
     the raw device interface should notify the driver by using a DIOCWLABEL
     ioctl function.

SEE ALSO
     disklabel(5), disklabel(8)

NetBSD 7.0                     December 26, 1996                    NetBSD 7.0

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