DISK(9)                NetBSD Kernel Developer's Manual                DISK(9)

     disk, disk_init, disk_attach, disk_begindetach, disk_detach,
     disk_destroy, disk_wait, disk_busy, disk_unbusy, disk_isbusy, disk_find,
     disk_set_info -- generic disk framework

     #include <sys/types.h>
     #include <sys/disklabel.h>
     #include <sys/disk.h>

     disk_init(struct disk *, const char *name,
         const struct dkdriver *driver);

     disk_attach(struct disk *);

     disk_begindetach(struct disk *, int (*lastclose)(device_t),
         device_t self, int flags);

     disk_detach(struct disk *);

     disk_destroy(struct disk *);

     disk_wait(struct disk *);

     disk_busy(struct disk *);

     disk_unbusy(struct disk *, long bcount, int read);

     disk_isbusy(struct disk *);

     struct disk *
     disk_find(const char *);

     disk_set_info(device_t, struct disk *, const char *type);

     The NetBSD generic disk framework is designed to provide flexible, scal-
     able, and consistent handling of disk state and metrics information.  The
     fundamental component of this framework is the disk structure, which is
     defined as follows:

     struct disk {
             TAILQ_ENTRY(disk) dk_link;      /* link in global disklist */
             const char      *dk_name;       /* disk name */
             prop_dictionary_t dk_info;      /* reference to disk-info dictionary */
             int             dk_bopenmask;   /* block devices open */
             int             dk_copenmask;   /* character devices open */
             int             dk_openmask;    /* composite (bopen|copen) */
             int             dk_state;       /* label state   ### */
             int             dk_blkshift;    /* shift to convert DEV_BSIZE to blks */
             int             dk_byteshift;   /* shift to convert bytes to blks */

              * Metrics data; note that some metrics may have no meaning
              * on certain types of disks.
             struct io_stats *dk_stats;

             const struct dkdriver *dk_driver;       /* pointer to driver */

              * Information required to be the parent of a disk wedge.
             kmutex_t        dk_rawlock;     /* lock on these fields */
             u_int           dk_rawopens;    /* # of opens of rawvp */
             struct vnode    *dk_rawvp;      /* vnode for the RAW_PART bdev */

             kmutex_t        dk_openlock;    /* lock on these and openmask */
             u_int           dk_nwedges;     /* # of configured wedges */
                                             /* all wedges on this disk */
             LIST_HEAD(, dkwedge_softc) dk_wedges;

              * Disk label information.  Storage for the in-core disk label
              * must be dynamically allocated, otherwise the size of this
              * structure becomes machine-dependent.
             daddr_t         dk_labelsector;         /* sector containing label */
             struct disklabel *dk_label;     /* label */
             struct cpu_disklabel *dk_cpulabel;

     The system maintains a global linked-list of all disks attached to the
     system.  This list, called disklist, may grow or shrink over time as
     disks are dynamically added and removed from the system.  Drivers which
     currently make use of the detachment capability of the framework are the
     ccd, dm, and vnd pseudo-device drivers.

     The following is a brief description of each function in the framework:

     disk_init()      Initialize the disk structure.

     disk_attach()    Attach a disk; allocate storage for the disklabel, set
                      the ``attached time'' timestamp, insert the disk into
                      the disklist, and increment the system disk count.

                      Check whether the disk is open, and if not, return 0.
                      If the disk is open, and DETACH_FORCE is not set in
                      flags, return EBUSY.  Otherwise, call the provided
                      lastclose routine (if not NULL) and return its exit

     disk_detach()    Detach a disk; free storage for the disklabel, remove
                      the disk from the disklist, and decrement the system
                      disk count.  If the count drops below zero, panic.

     disk_destroy()   Release resources used by the disk structure when it is
                      no longer required.

     disk_wait()      Disk timings are measured by counting the number of
                      queued requests (wait counter) and requests issued to
                      the hardware (busy counter) and keeping timestamp when
                      the counters change.  The time interval between two
                      changes of a counter is accumulated into a total and
                      also multiplied by the counter value and the accumulated
                      into a sum.  Both values can be used to determine how
                      much time is spent in the driver queue or in-flight to
                      the hardware as well as the average number of requests
                      in either state.  disk_wait() increment the disk's wait
                      counter and handles the accumulation.

     disk_busy()      Decrements the disk's wait counter and increments the
                      disk's ``busy counter'', and handles either accumula-
                      tion.  If the wait counter is still zero, it is assumed
                      that the driver hasn't been updated to call disk_wait(),
                      then only the values from the busy counter are avail-

     disk_unbusy()    Decrement the disk's busy counter and handles the accu-
                      mulation.  The third argument read specifies the direc-
                      tion of I/O; if non-zero it means reading from the disk,
                      otherwise it means writing to the disk.

     disk_isbusy()    Returns true if disk is marked as busy and false if it
                      is not.

     disk_find()      Return a pointer to the disk structure corresponding to
                      the name provided, or NULL if the disk does not exist.

     disk_set_info()  Setup disk-info dictionary and other dependent values of
                      the disk structure, the driver must have initialized the
                      dk_geom member of struct disk with suitable values.  If
                      type is not NULL, it will be added to the dictionary.

     The functions typically called by device drivers are disk_init()
     disk_attach(), disk_begindetach(), disk_detach(), disk_destroy(),
     disk_wait(), disk_busy(), disk_unbusy(), and disk_set_info().  The func-
     tion disk_find() is provided as a utility function.

     The following ioctls should be implemented by disk drivers:

     DIOCGDINFO struct disklabel
             Get disklabel.

     DIOCSDINFO struct disklabel
             Set in-memory disklabel.

     DIOCWDINFO struct disklabel
             Set in-memory disklabel and write on-disk disklabel.

     DIOCGPART struct partinfo
             Get partition information.  This is used internally.

     DIOCRFORMAT struct format_op
             Read format.

     DIOCWFORMAT struct format_op
             Write format.

     DIOCSSTEP int
             Set step rate.

             Set number of retries.

             Specify whether to keep or drop the in-memory disklabel when the
             device is closed.

             Enable or disable writing to the part of the disk that contains
             the label.

     DIOCSBAD struct dkbad
             Set kernel dkbad.

     DIOCEJECT int
             Eject removable disk.

     DIOCLOCK int
             Lock or unlock disk pack.  For devices with removable media,
             locking is intended to prevent the operator from removing the

     DIOCGDEFLABEL struct disklabel
             Get default label.

             Clear disk label.

             Get status of disk read and write caches.  The result is a bit-
             mask containing the following values:

             DKCACHE_READ     Read cache enabled.

             DKCACHE_WRITE    Write(back) cache enabled.

             DKCACHE_RCHANGE  Read cache enable is changeable.

             DKCACHE_WCHANGE  Write cache enable is changeable.

             DKCACHE_SAVE     Cache parameters may be saved, so that they per-
                              sist across reboots or device detach/attach

             Set status of disk read and write caches.  The input is a bitmask
             in the same format as used for DIOCGCACHE.

             Synchronise the disk cache.  This causes information in the
             disk's write cache (if any) to be flushed to stable storage.  The
             argument specifies whether or not to force a flush even if the
             kernel believes that there is no outstanding data.

     DIOCBSLIST struct disk_badsecinfo
             Get bad sector list.

             Flush bad sector list.

     DIOCAWEDGE struct dkwedge_info
             Add wedge.

     DIOCGWEDGEINFO struct dkwedge_info
             Get wedge information.

     DIOCDWEDGE struct dkwedge_info
             Delete wedge.

     DIOCLWEDGES struct dkwedge_list
             List wedges.

     DIOCGSTRATEGY struct disk_strategy
             Get disk buffer queue strategy.

     DIOCSSTRATEGY struct disk_strategy
             Set disk buffer queue strategy.

     DIOCGDISKINFO struct plistref
             Get disk-info dictionary.

             Get disk size in bytes.

             Get sector size in bytes.

     This section includes a description on basic use of the framework and
     example usage of its functions.  Actual implementation of a device driver
     which uses the framework may vary.

     Each device in the system uses a ``softc'' structure which contains auto-
     configuration and state information for that device.  In the case of
     disks, the softc should also contain one instance of the disk structure,

     struct foo_softc {
             device_t        sc_dev;         /* generic device information */
             struct  disk    sc_dk;          /* generic disk information */
             [ . . . more . . . ]

     In order for the system to gather metrics data about a disk, the disk
     must be registered with the system.  The disk_attach() routine performs
     all of the functions currently required to register a disk with the sys-
     tem including allocation of disklabel storage space, recording of the
     time since boot that the disk was attached, and insertion into the
     disklist.  Note that since this function allocates storage space for the
     disklabel, it must be called before the disklabel is read from the media
     or used in any other way.  Before disk_attach() is called, a portions of
     the disk structure must be initialized with data specific to that disk.
     For example, in the ``foo'' disk driver, the following would be performed
     in the autoconfiguration ``attach'' routine:

     fooattach(device_t parent, device_t self, void *aux)
             struct foo_softc *sc = device_private(self);
             [ . . . ]

             /* Initialize and attach the disk structure. */
             disk_init(&sc->sc_dk, device_xname(self), &foodkdriver);

             /* Read geometry and fill in pertinent parts of disklabel. */
             /* Initialize geometry values of the disk structure */
             [ . . . ]
             disk_set_info(&self>, &sc->sc_dk, type);

     The foodkdriver above is the disk's ``driver'' switch.  This switch cur-
     rently includes pointers to several driver entry points, where only the
     d_strategy entry point is used by the disk framework.  This switch needs
     to have global scope and should be initialized as follows:

     void    (foostrategy)(struct buf *);
     void    (foominphys)(struct buf *);
     int     (fooopen)(dev_t, int, int, struct lwp *);
     int     (fooclose)(dev_t, int, int, struct lwp *);
     int     (foo_discard)(device_t, off_t, off_t);
     int     (foo_diskstart)(device_t, struct buf *);
     void    (foo_iosize)(device_t, int *);
     int     (foo_dumpblocks)(device_t, void *, daddr_t, int);
     int     (foo_lastclose)(device_t);
     int     (foo_firstopen)(device_t, dev_t, int, int);
     int     (foo_label)(device_t, struct disklabel *);

     const struct dkdriver foodkdriver = {
             .d_open = fooopen,
             .d_close = fooclose,
             .d_strategy = foostrategy,
             .d_minphys = foominphys,
             .d_discard = foo_discard,
             .d_diskstart = foo_diskstart,   /* optional */
             .d_dumpblocks = foo_dumpblocks, /* optional */
             .d_iosize = foo_iosize,         /* optional */
             .d_firstopen = foo_firstopen,   /* optional */
             .d_lastclose = foo_lastclose,   /* optional */
             .d_label = foo_label,           /* optional */

     Once the disk is attached, metrics may be gathered on that disk.  In
     order to gather metrics data, the driver must tell the framework when the
     disk queues, starts and stops operations.  This functionality is provided
     by the disk_wait(), disk_busy() and disk_unbusy() routines.  Because
     struct disk is part of device driver private data it needs to be guarded.
     Mutual exclusion must be done by driver disk_wait(), disk_busy() and
     disk_unbusy() are not thread safe.  The disk_busy() routine should be
     called immediately before a command to the disk is sent, e.g.:

     foostrategy(struct buf *bp)
             [ . . . ]


             /* Put buffer onto drive's transfer queue */



     foostart(struct foo_softc *sc)
             [ . . . ]

             /* Get buffer from drive's transfer queue. */
             [ . . . ]

             /* Build command to send to drive. */
             [ . . . ]

             /* Tell the disk framework we're going busy. */

             /* Send command to the drive. */
             [ . . . ]

     The routine disk_unbusy() performs some consistency checks, such as
     ensuring that the calls to disk_busy() and disk_unbusy() are balanced.
     It also performs the final steps of the metrics calcuation.  A byte count
     is added to the disk's running total, and if greater than zero, the num-
     ber of transfers the disk has performed is incremented.  The third argu-
     ment read specifies the direction of I/O; if non-zero it means reading
     from the disk, otherwise it means writing to the disk.

             struct foo_xfer *xfer;
             struct foo_softc = (struct foo_softc *)xfer->xf_softc;
             struct buf *bp = xfer->xf_buf;
             long nbytes;
             [ . . . ]

              * Get number of bytes transferred.  If there is no buf
              * associated with the xfer, we are being called at the
              * end of a non-I/O command.
             if (bp == NULL)
                     nbytes = 0;
                     nbytes = bp->b_bcount - bp->b_resid;

             [ . . . ]

             /* Notify the disk framework that we've completed the transfer. */
             disk_unbusy(&sc->sc_dk, nbytes,
                 bp != NULL ? bp->b_flags & B_READ : 0);

             [ . . . ]

     disk_isbusy() is used to get status of disk device it returns true if
     device is currently busy and false if it is not.  Like disk_wait(),
     disk_busy() and disk_unbusy() it requires explicit locking from user

     The disk framework itself is implemented within the file
     sys/kern/subr_disk.c.  Data structures and function prototypes for the
     framework are located in sys/sys/disk.h.

     The NetBSD machine-independent SCSI disk and CD-ROM drivers use the disk
     framework.  They are located in sys/scsi/sd.c and sys/scsi/cd.c.

     The NetBSD ccd, dm, and vnd drivers use the detachment capability of the
     framework.  They are located in sys/dev/ccd.c, sys/dev/vnd.c, and

     ccd(4), dm(4), vnd(4), dksubr(9)

     The NetBSD generic disk framework appeared in NetBSD 1.2.

     The NetBSD generic disk framework was architected and implemented by
     Jason R. Thorpe <thorpej@NetBSD.org>.

NetBSD 7.0                       March 5, 2017                      NetBSD 7.0

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