diff options
| author | Benjamin Marzinski <bmarzins@redhat.com> | 2014-08-13 13:53:43 -0500 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2014-10-05 20:03:35 -0400 |
| commit | 86f1152b117a404229fd6f08ec3faca779f37b92 (patch) | |
| tree | dceee3703ab97065c3e425b55d42cb4edb9a079b /drivers/md/dm.h | |
| parent | 1f271972478d84dd9e4d6dd82f414d70ed9e78ce (diff) | |
dm: allow active and inactive tables to share dm_devs
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: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md/dm.h')
| -rw-r--r-- | drivers/md/dm.h | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/drivers/md/dm.h b/drivers/md/dm.h index e81d2152fa68..988c7fb7b145 100644 --- a/drivers/md/dm.h +++ b/drivers/md/dm.h @@ -44,7 +44,7 @@ struct dm_dev_internal { struct list_head list; atomic_t count; - struct dm_dev dm_dev; + struct dm_dev *dm_dev; }; struct dm_table; @@ -188,6 +188,9 @@ int dm_cancel_deferred_remove(struct mapped_device *md); int dm_request_based(struct mapped_device *md); sector_t dm_get_size(struct mapped_device *md); struct request_queue *dm_get_md_queue(struct mapped_device *md); +int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode, + struct dm_dev **result); +void dm_put_table_device(struct mapped_device *md, struct dm_dev *d); struct dm_stats *dm_get_stats(struct mapped_device *md); int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action, |