linux-toradex.git/drivers/md/persistent-data/dm-block-manager.h, branch v3.10.69

dm transaction manager: fix corruption due to non-atomic transaction commit

2014-05-13T11:59:45+00:00

commit a9d45396f5956d0b615c7ae3b936afd888351a47 upstream.

The persistent-data library used by dm-thin, dm-cache, etc is
transactional.  If anything goes wrong, such as an io error when writing
new metadata or a power failure, then we roll back to the last
transaction.

Atomicity when committing a transaction is achieved by:

a) Never overwriting data from the previous transaction.
b) Writing the superblock last, after all other metadata has hit the
   disk.

This commit and the following commit ("dm: take care to copy the space
map roots before locking the superblock") fix a bug associated with (b).
When committing it was possible for the superblock to still be written
in spite of an io error occurring during the preceeding metadata flush.
With these commits we're careful not to take the write lock out on the
superblock until after the metadata flush has completed.

Change the transaction manager's semantics for dm_tm_commit() to assume
all data has been flushed _before_ the single superblock that is passed
in.

As a prerequisite, split the block manager's block unlocking and
flushing by simplifying dm_bm_flush_and_unlock() to dm_bm_flush().  Now
the unlocking must be done separately.

This issue was discovered by forcing io errors at the crucial time
using dm-flakey.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Greg Kroah-Hartman

dm persistent data: introduce dm_bm_set_read_only

2012-07-27T14:08:15+00:00

Introduce dm_bm_set_read_only to switch the block manager into a
read-only mode.  To be used when dm-thin degrades due to io errors on
the metadata device.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm persistent data: stop using dm_bm_unlock_move when shadowing blocks in tm

2012-07-27T14:08:09+00:00

Stop using dm_bm_unlock_move when shadowing blocks in the transaction
manager as an optimisation and remove the function as it is then no
longer used.

Some code, such as the space maps, keeps using on-disk data structures
from the previous transaction.  It can do this because blocks won't
be reallocated until the subsequent transaction.  Using
dm_bm_unlock_move to copy blocks sounds like a win, but it forces a
synchronous read should the old block be accessed.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm: add persistent data library

2011-10-31T20:19:11+00:00

The persistent-data library offers a re-usable framework for the storage
and management of on-disk metadata in device-mapper targets.

It's used by the thin-provisioning target in the next patch and in an
upcoming hierarchical storage target.

For further information, please read
Documentation/device-mapper/persistent-data.txt

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon