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authorChristoph Hellwig <hch@lst.de>2019-02-18 09:38:49 -0800
committerDarrick J. Wong <darrick.wong@oracle.com>2019-02-21 07:55:07 -0800
commit66ae56a53f0e34113da1a70068422b9444fe66f0 (patch)
tree846ea1eb3662294f44288d7ef9218ce0f0d0fc1c /fs/xfs/xfs_super.c
parentc4feb0b194f37b33514ee30a9e86a68194a1361e (diff)
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xfs: introduce an always_cow mode
Add a mode where XFS never overwrites existing blocks in place. This is to aid debugging our COW code, and also put infatructure in place for things like possible future support for zoned block devices, which can't support overwrites. This mode is enabled globally by doing a: echo 1 > /sys/fs/xfs/debug/always_cow Note that the parameter is global to allow running all tests in xfstests easily in this mode, which would not easily be possible with a per-fs sysfs file. In always_cow mode persistent preallocations are disabled, and fallocate will fail when called with a 0 mode (with our without FALLOC_FL_KEEP_SIZE), and not create unwritten extent for zeroed space when called with FALLOC_FL_ZERO_RANGE or FALLOC_FL_UNSHARE_RANGE. There are a few interesting xfstests failures when run in always_cow mode: - generic/392 fails because the bytes used in the file used to test hole punch recovery are less after the log replay. This is because the blocks written and then punched out are only freed with a delay due to the logging mechanism. - xfs/170 will fail as the already fragile file streams mechanism doesn't seem to interact well with the COW allocator - xfs/180 xfs/182 xfs/192 xfs/198 xfs/204 and xfs/208 will claim the file system is badly fragmented, but there is not much we can do to avoid that when always writing out of place - xfs/205 fails because overwriting a file in always_cow mode will require new space allocation and the assumption in the test thus don't work anymore. - xfs/326 fails to modify the file at all in always_cow mode after injecting the refcount error, leading to an unexpected md5sum after the remount, but that again is expected Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs/xfs_super.c')
-rw-r--r--fs/xfs/xfs_super.c15
1 files changed, 11 insertions, 4 deletions
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 08033ac040d6..f093ea244849 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1736,11 +1736,18 @@ xfs_fs_fill_super(
}
}
- if (xfs_sb_version_hasreflink(&mp->m_sb) && mp->m_sb.sb_rblocks) {
- xfs_alert(mp,
+ if (xfs_sb_version_hasreflink(&mp->m_sb)) {
+ if (mp->m_sb.sb_rblocks) {
+ xfs_alert(mp,
"reflink not compatible with realtime device!");
- error = -EINVAL;
- goto out_filestream_unmount;
+ error = -EINVAL;
+ goto out_filestream_unmount;
+ }
+
+ if (xfs_globals.always_cow) {
+ xfs_info(mp, "using DEBUG-only always_cow mode.");
+ mp->m_always_cow = true;
+ }
}
if (xfs_sb_version_hasrmapbt(&mp->m_sb) && mp->m_sb.sb_rblocks) {