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author | Benjamin Marzinski <bmarzins@redhat.com> | 2014-08-13 13:53:43 -0500 |
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committer | Mike Snitzer <snitzer@redhat.com> | 2014-10-05 20:03:35 -0400 |
commit | 86f1152b117a404229fd6f08ec3faca779f37b92 (patch) | |
tree | dceee3703ab97065c3e425b55d42cb4edb9a079b /include/video/of_videomode.h | |
parent | 1f271972478d84dd9e4d6dd82f414d70ed9e78ce (diff) | |
download | op-kernel-dev-86f1152b117a404229fd6f08ec3faca779f37b92.zip op-kernel-dev-86f1152b117a404229fd6f08ec3faca779f37b92.tar.gz |
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 'include/video/of_videomode.h')
0 files changed, 0 insertions, 0 deletions