This is the help page for the new dminfo extension:

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NAME
  dminfo - device mapper (dm) information

SYNOPSIS
  dminfo [-b bio | -d | -l | -q | -s | -t]

DESCRIPTION
  This command displays information about device-mapper mapped
  devices (dm devices).
  If no argument is entered, displays lists of existing dm devices.
  It's same as -l option.

    -b bio  displays the information of the dm device which the bio
            is submitted in.  If the bio isn't for dm devices,
            results will be error.
        -d  displays dependency information for existing dm devices.
        -l  displays lists of existing dm devices.
        -q  displays queued I/O information for each target of
            existing dm devices.
        -s  displays status information for each target of existing
            dm devices.
        -t  displays table information for each target of existing
            dm devices.

EXAMPLE
  Display lists of dm devices.  "MAP_DEV" is the address of the
  struct mapped_device.  "DM_TABLE" is the address of the struct
  dm_table.  "TARGETS" is the number of targets which are in
  the struct dm_table.

    crash> dminfo
    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  8    c4866c80          c4866280          1        vg0-snap0
    253  6    f6a04a80          f6a04580          1        vg0-lv0-real
    253  0    c4840380          c4841880          1        mp0
    253  5    f7c50c80          c488e480          1        via_cbeheddbdd
    253  7    c4866a80          c4866380          1        vg0-snap0-cow
    253  4    d441e280          c919ed80          1        dummy1
    253  3    f5dc4280          cba81d80          1        dummy0
    253  2    f7c53180          c4866180          1        vg0-lv0
    253  1    f746d280          f746cd80          1        mp0p1

  Display the dm device information which the bio is submitted in.
  The bio (ceacee80) is a clone of the bio (ceacee00) which is
  submitted in the dm-3 (dummy0).  And the bio (ceacee00) is a clone
  of the bio (ceaced80) which is submitted in the dm-4 (dummy1), too.
  The bio (ceaced80) is the original bio.

    crash> dminfo -b ceacee80
    DM_BIO_ADDRESS    MAJ  MIN  MAP_DEV           DEVNAME
    ceacee00          253  3    f5dc4280          dm-3
    crash> dminfo -b ceacee00
    DM_BIO_ADDRESS    MAJ  MIN  MAP_DEV           DEVNAME
    ceaced80          253  4    d441e280          dm-4
    crash> dminfo -b ceaced80
    dminfo: invalid kernel virtual address: 64  type: "GET_VALUE: dm_io.bio"

  Display dependency information for each target.
  The vg0-snap0 depends on thd dm-6 (vg0-lv0-real) and the dm-7
  (vg0-snap0-cow)

    crash> dminfo -d
    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  8    c4866c80          c4866280          1        vg0-snap0
      MAJ  MIN  GENDISK           COUNT  DEVNAME
      253  7    c4866980          1      dm-7
      253  6    f6a04280          1      dm-6

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  6    f6a04a80          f6a04580          1        vg0-lv0-real
      MAJ  MIN  GENDISK           COUNT  DEVNAME
      8    0    f7f24c80          1      sda

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  7    c4866a80          c4866380          1        vg0-snap0-cow
      MAJ  MIN  GENDISK           COUNT  DEVNAME
      8    0    f7f24c80          1      sda

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  2    f7c53180          c4866180          1        vg0-lv0
      MAJ  MIN  GENDISK           COUNT  DEVNAME
      253  6    f6a04280          1      dm-6

  Display queued I/O information for each target.
  The information is displayed under the "PRIVATE_DATA" column.

    crash> dminfo -q
    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  5    f7c50c80          c488e480          1        via_cbeheddbdd
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8961080          mirror       (reads) (writes) (quiesced) (recovered)

      --------------------------------------------------------------
       "reads/writes" are members of the struct mirror_set, and
       "quiesced/recovered" are members of the struct region_hash.
       If the list is empty, the member is bracketed by "()".
      --------------------------------------------------------------

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  0    c4840380          c4841880          1        mp0
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8802080          multipath    queue_size:0

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  1    f746d280          f746cd80          1        mp0p1
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8821080          linear       No queue info

  Display status information for each target.
  The information is displayed under the "PRIVATE_DATA" column.

    crash> dminfo -s
    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  0    c4840380          c4841880          1        mp0
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8802080          multipath    queue_if_no_path:0 hwh:none nr_pgs:1
        PG  PG_STATUS  NR_PATHS  PATHS
        1   active     2         8:16(A,0) 8:32(A,0)

      --------------------------------------------------------------
       Format of "PATHS": <major>:<minor>(<status>,<fail_count>)
         Status: A:active, F:faulty
         Fail_count: the value of the struct pgpath.fail_count
      --------------------------------------------------------------

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  5    f7c50c80          c488e480          1        via_cbeheddbdd
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8961080          mirror       in_sync:1 dev:8:16(A,0),8:32(A,0)

      --------------------------------------------------------------
       Format of "dev": <major>:<minor>(<status>,<error_count>)
         Status: A:active, D:degraded
         Error_count: the value of the struct mirror.error_count
      --------------------------------------------------------------

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  1    f746d280          f746cd80          1        mp0p1
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8821080          linear       No status info

  Display table information for each target.
  The information is displayed under the "PRIVATE_DATA" column.

    crash> dminfo -t
    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  8    c4866c80          c4866280          1        vg0-snap0
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f89b4080          snapshot     orig:253:6 cow:253:7 type:P chunk_size:16

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  6    f6a04a80          f6a04580          1        vg0-lv0-real
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f890f080          linear       begin:0 len:204800 dev:8:5 offset:384

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  0    c4840380          c4841880          1        mp0
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8802080          multipath    queue_if_no_path:0 hwh:none nr_pgs:1
        PG  PATH_SELECTOR  NR_PATHS  PATHS
        1   round-robin    2         8:16 8:32

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  5    f7c50c80          c488e480          1        via_cbeheddbdd
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8961080          mirror       log:core dev:8:16(0),8:32(0)

      --------------------------------------------------------------
       Format of "dev": <major>:<minor>(<offset>)
         Offset: the value of the struct mirror.offset
      --------------------------------------------------------------

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  7    c4866a80          c4866380          1        vg0-snap0-cow
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f899d080          linear       begin:0 len:8192 dev:8:5 offset:205184

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  2    f7c53180          c4866180          1        vg0-lv0
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8bbc080          snapshot-origin  orig_dev:253:6

    MAJ  MIN  MAP_DEV           DM_TABLE          TARGETS  MAPNAME
    253  1    f746d280          f746cd80          1        mp0p1
      TARGET            TARGET_TYPE  PRIVATE_DATA
      f8821080          linear       begin:0 len:2040192 dev:253:0 offset:63