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Etienne Dechamps b18019d2d8 Fix synchronicity for ZVOLs. 
zvol_write() assumes that the write request must be written to stable storage
if rq_is_sync() is true. Unfortunately, this assumption is incorrect. Indeed,
"sync" does *not* mean what we think it means in the context of the Linux
block layer. This is well explained in linux/fs.h:

    WRITE:       A normal async write. Device will be plugged.
    WRITE_SYNC:  Synchronous write. Identical to WRITE, but passes down
                 the hint that someone will be waiting on this IO
                 shortly.
    WRITE_FLUSH: Like WRITE_SYNC but with preceding cache flush.
    WRITE_FUA:   Like WRITE_SYNC but data is guaranteed to be on
                 non-volatile media on completion.

In other words, SYNC does not *mean* that the write must be on stable storage
on completion. It just means that someone is waiting on us to complete the
write request. Thus triggering a ZIL commit for each SYNC write request on a
ZVOL is unnecessary and harmful for performance. To make matters worse, ZVOL
users have no way to express that they actually want data to be written to
stable storage, which means the ZIL is broken for ZVOLs.

The request for stable storage is expressed by the FUA flag, so we must
commit the ZIL after the write if the FUA flag is set. In addition, we must
commit the ZIL before the write if the FLUSH flag is set.

Also, we must inform the block layer that we actually support FLUSH and FUA.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
 		2012-02-07 16:23:06 -08:00
..
fm Fix synchronicity for ZVOLs. 2012-02-07 16:23:06 -08:00
fs Fix synchronicity for ZVOLs. 2012-02-07 16:23:06 -08:00
Makefile.am Add the release component to headers 2012-01-18 12:19:47 -08:00
Makefile.in Fix synchronicity for ZVOLs. 2012-02-07 16:23:06 -08:00
arc.h Linux 3.1 compat, super_block->s_shrink 2012-01-11 11:46:02 -08:00
avl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
avl_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
bplist.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
bpobj.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dbuf.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
ddt.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dmu.h Illumos #755: dmu_recv_stream builds incomplete guid_to_ds_map 2011-10-18 11:18:14 -07:00
dmu_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dmu_objset.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dmu_traverse.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dmu_tx.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dmu_zfetch.h Add missing ZFS tunables 2011-05-04 10:02:37 -07:00
dnode.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_dataset.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_deadlist.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_deleg.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_dir.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_pool.h Prototype/structure update for Linux 2011-02-10 09:27:21 -08:00
dsl_prop.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_scan.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
dsl_synctask.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
efi_partition.h Make libefi-created GPT compatible with gptfdisk 2011-09-26 09:44:43 -07:00
metaslab.h Illumos #1051: zfs should handle imbalanced luns 2011-08-01 12:09:11 -07:00
metaslab_impl.h Illumos #1051: zfs should handle imbalanced luns 2011-08-01 12:09:11 -07:00
nvpair.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
nvpair_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
refcount.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
rrwlock.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
sa.h Implement SA based xattrs 2011-11-28 15:45:51 -08:00
sa_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
spa.h Illumos #1051: zfs should handle imbalanced luns 2011-08-01 12:09:11 -07:00
spa_boot.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
spa_impl.h Illumos #1051: zfs should handle imbalanced luns 2011-08-01 12:09:11 -07:00
space_map.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
txg.h Add API to wait for pending commit callbacks 2011-02-16 11:20:06 -08:00
txg_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
u8_textprep.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
u8_textprep_data.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
uberblock.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
uberblock_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
uio_impl.h Add basic uio support 2011-02-10 09:21:43 -08:00
unique.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
uuid.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
vdev.h Add missing ZFS tunables 2011-05-04 10:02:37 -07:00
vdev_disk.h Linux 2.6.x compat, blkdev_compat.h 2011-02-23 12:29:38 -08:00
vdev_file.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
vdev_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
xvattr.h Add xvattr support 2011-03-02 11:43:50 -08:00
zap.h Export symbols for the full ZAP API 2011-09-27 16:12:36 -07:00
zap_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zap_leaf.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_acl.h Add xvattr support 2011-03-02 11:43:50 -08:00
zfs_context.h Cleanup ZFS debug infrastructure 2012-02-02 11:24:30 -08:00
zfs_debug.h Cleanup ZFS debug infrastructure 2012-02-02 11:24:30 -08:00
zfs_dir.h Prototype/structure update for Linux 2011-02-10 09:27:21 -08:00
zfs_fuid.h Prototype/structure update for Linux 2011-02-10 09:27:21 -08:00
zfs_ioctl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_onexit.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_rlock.h Range lock performance improvements 2011-03-08 12:44:06 -08:00
zfs_sa.h Implement SA based xattrs 2011-11-28 15:45:51 -08:00
zfs_stat.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_vfsops.h Increase link count limit to 2^31-1 2012-01-13 11:43:59 -08:00
zfs_vnops.h Cleanup mmap(2) writes 2011-08-02 10:34:55 -07:00
zfs_znode.h Implement SA based xattrs 2011-11-28 15:45:51 -08:00
zil.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zil_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zio.h Illumos #734: Use taskq_dispatch_ent() interface 2011-12-14 09:19:30 -08:00
zio_checksum.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zio_compress.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zio_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zpl.h Linux 3.1 compat, super_block->s_shrink 2012-01-11 11:46:02 -08:00
zrlock.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zvol.h Linux 2.6.x compat, blkdev_compat.h 2011-02-23 12:29:38 -08:00