• Benjamin Marzinski's avatar
    dm: allow active and inactive tables to share dm_devs · 86f1152b
    Benjamin Marzinski authored
    Until this change, when loading a new DM table, DM core would re-open
    all of the devices in the DM table.  Now, DM core will avoid redundant
    device opens (and closes when destroying the old table) if the old
    table already has a device open using the same mode.  This is achieved
    by managing reference counts on the table_devices that DM core now
    stores in the mapped_device structure (rather than in the dm_table
    structure).  So a mapped_device's active and inactive dm_tables' dm_dev
    lists now just point to the dm_devs stored in the mapped_device's
    table_devices list.
    
    This improvement in DM core's device reference counting has the
    side-effect of fixing a long-standing limitation of the multipath
    target: a DM multipath table couldn't include any paths that were unusable
    (failed).  For example: if all paths have failed and you add a new,
    working, path to the table; you can't use it since the table load would
    fail due to it still containing failed paths.  Now a re-load of a
    multipath table can include failed devices and when those devices become
    active again they can be used instantly.
    
    The device list code in dm.c isn't a straight copy/paste from the code in
    dm-table.c, but it's very close (aside from some variable renames).  One
    subtle difference is that find_table_device for the tables_devices list
    will only match devices with the same name and mode.  This is because we
    don't want to upgrade a device's mode in the active table when an
    inactive table is loaded.
    
    Access to the mapped_device structure's tables_devices list requires a
    mutex (tables_devices_lock), so that tables cannot be created and
    destroyed concurrently.
    Signed-off-by: default avatarBenjamin Marzinski <bmarzins@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    86f1152b
dm-table.c 38.5 KB