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Subject[PATCHSET 2.6.36-rc2] block, dm: finish REQ_FLUSH/FUA conversion

This patchset converts dm to REQ_FLUSH/FUA, which was the last
remaining one. I've put patches on top of the previous patches for
easier review. The series can be trivially reordered so that the
order is more logical. Jens, please let me know if you want it to be

The dm conversion is _lightly_ tested. Please proceed with caution.
In particular, I haven't tested dm implementation at all. So, it
probably is best to hold off merging these bits until dm people can
verify the conversion is correct.


Differences from the previous attempt[1] are,

* I was wrong when I wrote that flush retry logic was dropped. What
got dropped was -EOPNOTSUPP handling. The retry behavior used by
multipath remains the same. As blindly retrying flushes could be
dangerous, a FIXME comment is added.

* bio-based dm now also advertises REQ_FLUSH | REQ_FUA capability as
block layer now filters out REQ_FLUSH if not supported by the queue.

* 0002-dm-implement-REQ_FLUSH-FUA-support.patch added to update
__blk_rq_prep_clone() to copy most REQ_* flags including FLUSH and
FUA and request-based dm now advertises REQ_FLUSH | REQ_FUA support.

* dm_request_fn() now explicitly plugs other requests while a flush
request is in progress. This is to avoid starving flush sequence
which uses device draining to check whether each step is complete.

* 0003-block-remove-the-WRITE_BARRIER-flag.patch added to drop
needless ordering around flush handling.

This patchset is on top of "block, fs: replace HARDBARRIER with
FLUSH/FUA" patchset[2] and available in the following git tree

git:// flush-fua

and contains the following changes.

block/blk-core.c | 4
drivers/md/dm-crypt.c | 2
drivers/md/dm-io.c | 20 --
drivers/md/dm-log.c | 2
drivers/md/dm-raid1.c | 8 -
drivers/md/dm-region-hash.c | 16 +-
drivers/md/dm-snap-persistent.c | 2
drivers/md/dm-snap.c | 6
drivers/md/dm-stripe.c | 2
drivers/md/dm.c | 277 +++++++++++++++-------------------------
include/linux/blk_types.h | 1
include/linux/fs.h | 3
12 files changed, 131 insertions(+), 212 deletions(-)




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