Pull second vfs pile from Al Viro:
"The stuff in there: fsfreeze deadlock fixes by Jan (essentially, the
deadlock reproduced by xfstests 068), symlink and hardlink restriction
patches, plus assorted cleanups and fixes.
Note that another fsfreeze deadlock (emergency thaw one) is *not*
dealt with - the series by Fernando conflicts a lot with Jan's, breaks
userland ABI (FIFREEZE semantics gets changed) and trades the deadlock
for massive vfsmount leak; this is going to be handled next cycle.
There probably will be another pull request, but that stuff won't be
in it."
Fix up trivial conflicts due to unrelated changes next to each other in
drivers/{staging/gdm72xx/usb_boot.c, usb/gadget/storage_common.c}
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (54 commits)
delousing target_core_file a bit
Documentation: Correct s_umount state for freeze_fs/unfreeze_fs
fs: Remove old freezing mechanism
ext2: Implement freezing
btrfs: Convert to new freezing mechanism
nilfs2: Convert to new freezing mechanism
ntfs: Convert to new freezing mechanism
fuse: Convert to new freezing mechanism
gfs2: Convert to new freezing mechanism
ocfs2: Convert to new freezing mechanism
xfs: Convert to new freezing code
ext4: Convert to new freezing mechanism
fs: Protect write paths by sb_start_write - sb_end_write
fs: Skip atime update on frozen filesystem
fs: Add freezing handling to mnt_want_write() / mnt_drop_write()
fs: Improve filesystem freezing handling
switch the protection of percpu_counter list to spinlock
nfsd: Push mnt_want_write() outside of i_mutex
btrfs: Push mnt_want_write() outside of i_mutex
fat: Push mnt_want_write() outside of i_mutex
...
We convert btrfs_file_aio_write() to use new freeze check. We also add proper
freeze protection to btrfs_page_mkwrite(). We also add freeze protection to
the transaction mechanism to avoid starting transactions on frozen filesystem.
At minimum this is necessary to stop iput() of unlinked file to change frozen
filesystem during truncation.
Checks in cleaner_kthread() and transaction_kthread() can be safely removed
since btrfs_freeze() will lock the mutexes and thus block the threads (and they
shouldn't have anything to do anyway).
CC: linux-btrfs@vger.kernel.org
CC: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Use the generic printk_get_level() to search a message for a kern_level.
Add __printf to verify format and arguments. Fix a few messages that
had mismatches in format and arguments. Add #ifdef CONFIG_PRINTK blocks
to shrink the object size a bit when not using printk.
[akpm@linux-foundation.org: whitespace tweak]
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When mnt_want_write() starts to handle freezing it will get a full lock
semantics requiring proper lock ordering. So push mnt_want_write() call
consistently outside of i_mutex.
CC: Chris Mason <chris.mason@oracle.com>
CC: linux-btrfs@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
On powerpc, we don't get the implicit vmalloc.h include, and as a result
the build fails noisily:
fs/btrfs/send.c: In function 'fs_path_free':
fs/btrfs/send.c:185:4: error: implicit declaration of function 'vfree' [-Werror=implicit-function-declaration]
fs/btrfs/send.c: In function 'fs_path_ensure_buf':
fs/btrfs/send.c:215:4: error: implicit declaration of function 'vmalloc' [-Werror=implicit-function-declaration]
fs/btrfs/send.c:215:12: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:225:12: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:233:13: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c: In function 'iterate_dir_item':
fs/btrfs/send.c:900:10: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:909:11: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c: In function 'btrfs_ioctl_send':
fs/btrfs/send.c:4463:17: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:4469:17: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:4475:2: error: implicit declaration of function 'vzalloc' [-Werror=implicit-function-declaration]
fs/btrfs/send.c:4475:20: warning: assignment makes pointer from integer without a cast [enabled by default]
fs/btrfs/send.c:4483:21: warning: assignment makes pointer from integer without a cast [enabled by default]
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull large btrfs update from Chris Mason:
"This pull request is very large, and the two main features in here
have been under testing/devel for quite a while.
We have subvolume quotas from the strato developers. This enables
full tracking of how many blocks are allocated to each subvolume (and
all snapshots) and you can set limits on a per-subvolume basis. You
can also create quota groups and toss multiple subvolumes into a big
group. It's everything you need to be a web hosting company and give
each user their own subvolume.
The userland side of the quotas is being refreshed, they'll send out
details on where to grab it soon.
Next is the kernel side of btrfs send/receive from Alexander Block.
This leverages the same infrastructure as the quota code to figure out
relationships between blocks and their owners. It can then compute
the difference between two snapshots and sends the diffs in a neutral
format into userland.
The basic model:
create a snapshot
send that snapshot as the initial backup
make changes
create a second snapshot
send the incremental as a backup
delete the first snapshot
(use the second snapshot for the next incremental)
The receive portion is all in userland, and in the 'next' branch of my
btrfs-progs repo.
There's still some work to do in terms of optimizing the send side
from kernel to userland. The really important part is figuring out
how two snapshots are different, and this is where we are
concentrating right now. The initial send of a dataset is a little
slower than tar, but the incremental sends are dramatically faster
than what rsync can do.
On top of all of that, we have a nice queue of fixes, cleanups and
optimizations."
Fix up trivial modify/del conflict in fs/btrfs/ioctl.c
Also fix up semantic conflict in fs/btrfs/send.c: the interface to
dentry_open() changed in commit 765927b2d5 ("switch dentry_open() to
struct path, make it grab references itself"), and since it now grabs
whatever references it needs, we should no longer do the mntget() on the
mnt (and we need to dput() the dentry reference we took).
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs: (65 commits)
Btrfs: uninit variable fixes in send/receive
Btrfs: introduce BTRFS_IOC_SEND for btrfs send/receive
Btrfs: add btrfs_compare_trees function
Btrfs: introduce subvol uuids and times
Btrfs: make iref_to_path non static
Btrfs: add a barrier before a waitqueue_active check
Btrfs: call the ordered free operation without any locks held
Btrfs: Check INCOMPAT flags on remount and add helper function
Btrfs: add helper for tree enumeration
btrfs: allow cross-subvolume file clone
Btrfs: improve multi-thread buffer read
Btrfs: make btrfs's allocation smoothly with preallocation
Btrfs: lock the transition from dirty to writeback for an eb
Btrfs: fix potential race in extent buffer freeing
Btrfs: don't return true in releasepage unless we actually freed the eb
Btrfs: suppress printk() if all device I/O stats are zero
Btrfs: remove unwanted printk() for btrfs device I/O stats
Btrfs: rewrite BTRFS_SETGET_FUNCS
Btrfs: zero unused bytes in inode item
Btrfs: kill free_space pointer from inode structure
...
Conflicts:
fs/btrfs/ioctl.c
This is the kernel portion of btrfs send/receive
Conflicts:
fs/btrfs/Makefile
fs/btrfs/backref.h
fs/btrfs/ctree.c
fs/btrfs/ioctl.c
fs/btrfs/ioctl.h
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
This patch introduces the BTRFS_IOC_SEND ioctl that is
required for send. It allows btrfs-progs to implement
full and incremental sends. Patches for btrfs-progs will
follow.
Signed-off-by: Alexander Block <ablock84@googlemail.com>
Reviewed-by: David Sterba <dave@jikos.cz>
Reviewed-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Reviewed-by: Alex Lyakas <alex.bolshoy.btrfs@gmail.com>
This function is used to find the differences between
two trees. The tree compare skips whole subtrees if it
detects shared tree blocks and thus is pretty fast.
Signed-off-by: Alexander Block <ablock84@googlemail.com>
Reviewed-by: David Sterba <dave@jikos.cz>
Reviewed-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Reviewed-by: Alex Lyakas <alex.bolshoy.btrfs@gmail.com>
This patch introduces uuids for subvolumes. Each
subvolume has it's own uuid. In case it was snapshotted,
it also contains parent_uuid. In case it was received,
it also contains received_uuid.
It also introduces subvolume ctime/otime/stime/rtime. The
first two are comparable to the times found in inodes. otime
is the origin/creation time and ctime is the change time.
stime/rtime are only valid on received subvolumes.
stime is the time of the subvolume when it was
sent. rtime is the time of the subvolume when it was
received.
Additionally to the times, we have a transid for each
time. They are updated at the same place as the times.
btrfs receive uses stransid and rtransid to find out
if a received subvolume changed in the meantime.
If an older kernel mounts a filesystem with the
extented fields, all fields become invalid. The next
mount with a new kernel will detect this and reset the
fields.
Signed-off-by: Alexander Block <ablock84@googlemail.com>
Reviewed-by: David Sterba <dave@jikos.cz>
Reviewed-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Reviewed-by: Alex Lyakas <alex.bolshoy.btrfs@gmail.com>
Each ordered operation has a free callback, and this was called with the
worker spinlock held. Josef made the free callback also call iput,
which we can't do with the spinlock.
This drops the spinlock for the free operation and grabs it again before
moving through the rest of the list. We'll circle back around to this
and find a cleaner way that doesn't bounce the lock around so much.
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
cc: stable@kernel.org
In support of the recently added capability to remount with lzo
compression, provide a helper function to check the compression
INCOMPAT flags when remounting with lzo compression, and set
the flags if necessary.
Also, implement the new helper function when defragmenting with
explicit lzo compression and when setting the default subvolume.
Signed-off-by: Mitch Harder <mitch.harder@sabayonlinux.org>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Often no exact match is wanted but just the next lower or
higher item. There's a lot of duplicated code throughout
btrfs to deal with the corner cases. This patch adds a
helper function that can facilitate searching.
Signed-off-by: Arne Jansen <sensille@gmx.net>
Lift the EXDEV condition and allow different root trees for files being
cloned, then pass source inode's root when searching for extents.
Cloning is not allowed to cross vfsmounts, ie. when two subvolumes from
one filesystem are mounted separately.
Signed-off-by: David Sterba <dsterba@suse.cz>
Pull trivial tree from Jiri Kosina:
"Trivial updates all over the place as usual."
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial: (29 commits)
Fix typo in include/linux/clk.h .
pci: hotplug: Fix typo in pci
iommu: Fix typo in iommu
video: Fix typo in drivers/video
Documentation: Add newline at end-of-file to files lacking one
arm,unicore32: Remove obsolete "select MISC_DEVICES"
module.c: spelling s/postition/position/g
cpufreq: Fix typo in cpufreq driver
trivial: typo in comment in mksysmap
mach-omap2: Fix typo in debug message and comment
scsi: aha152x: Fix sparse warning and make printing pointer address more portable.
Change email address for Steve Glendinning
Btrfs: fix typo in convert_extent_bit
via: Remove bogus if check
netprio_cgroup.c: fix comment typo
backlight: fix memory leak on obscure error path
Documentation: asus-laptop.txt references an obsolete Kconfig item
Documentation: ManagementStyle: fixed typo
mm/vmscan: cleanup comment error in balance_pgdat
mm: cleanup on the comments of zone_reclaim_stat
...
While testing with my buffer read fio jobs[1], I find that btrfs does not
perform well enough.
Here is a scenario in fio jobs:
We have 4 threads, "t1 t2 t3 t4", starting to buffer read a same file,
and all of them will race on add_to_page_cache_lru(), and if one thread
successfully puts its page into the page cache, it takes the responsibility
to read the page's data.
And what's more, reading a page needs a period of time to finish, in which
other threads can slide in and process rest pages:
t1 t2 t3 t4
add Page1
read Page1 add Page2
| read Page2 add Page3
| | read Page3 add Page4
| | | read Page4
-----|------------|-----------|-----------|--------
v v v v
bio bio bio bio
Now we have four bios, each of which holds only one page since we need to
maintain consecutive pages in bio. Thus, we can end up with far more bios
than we need.
Here we're going to
a) delay the real read-page section and
b) try to put more pages into page cache.
With that said, we can make each bio hold more pages and reduce the number
of bios we need.
Here is some numbers taken from fio results:
w/o patch w patch
------------- -------- ---------------
READ: 745MB/s +25% 934MB/s
[1]:
[global]
group_reporting
thread
numjobs=4
bs=32k
rw=read
ioengine=sync
directory=/mnt/btrfs/
[READ]
filename=foobar
size=2000M
invalidate=1
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
For backref walking, we've introduce delayed ref's sequence. However,
it changes our preallocation behavior.
The story is that when we preallocate an extent and then mark it written
piece by piece, the ideal case should be that we don't need to COW the
extent, which is why we use 'preallocate'.
But we may not make use of preallocation, since when we check for cross refs on
the extent, we may have two ref entries which have the same content except
the sequence value, and we recognize them as cross refs and do COW to allocate
another extent.
So we end up with several pieces of space instead of an whole extent.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
There is a small window where an eb can have no IO bits set on it, which
could potentially result in extent_buffer_under_io() returning false when we
want it to return true, which could result in not fun things happening. So
in order to protect this case we need to hold the refs_lock when we make
this transition to make sure we get reliable results out of
extent_buffer_udner_io(). Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
This sounds sort of impossible but it is the only thing I can think of and
at the very least it is theoretically possible so here it goes.
If we are in try_release_extent_buffer we will check that the ref count on
the extent buffer is 1 and not under IO, and then go down and clear the tree
ref. If between this check and clearing the tree ref somebody else comes in
and grabs a ref on the eb and the marks it dirty before
try_release_extent_buffer() does it's tree ref clear we can end up with a
dirty eb that will be freed while it is still dirty which will result in a
panic. Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
I noticed while looking at an extent_buffer race that we will
unconditionally return 1 if we get down to release_extent_buffer after
clearing the tree ref. However we can easily race in here and get a ref on
the eb and not actually free the eb. So make release_extent_buffer return 1
if it free'd the eb and 0 if not so we can be a little kinder to the vm.
Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Code is added to suppress the I/O stats printing at mount time if all
statistic values are zero.
Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
People complained about the annoying kernel log message
"btrfs: no dev_stats entry found ... (OK on first mount after mkfs)"
everytime a filesystem is mounted for the first time after running
mkfs. Since the distribution of the btrfs-progs is not synchronized
to the kernel version, mkfs like it is now will be used also in the
future. Then this message is not useful to find errors, it is just
annoying. This commit removes the printk().
Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
BTRFS_SETGET_FUNCS macro is used to generate btrfs_set_foo() and
btrfs_foo() functions, which read and write specific fields in the
extent buffer.
The total number of set/get functions is ~200, but in fact we only
need 8 functions: 2 for u8 field, 2 for u16, 2 for u32 and 2 for u64.
It results in redunction of ~37K bytes.
text data bss dec hex filename
629661 12489 216 642366 9cd3e fs/btrfs/btrfs.o.orig
592637 12489 216 605342 93c9e fs/btrfs/btrfs.o
Signed-off-by: Li Zefan <lizefan@huawei.com>
The otime field is not zeroed, so users will see random otime in an old
filesystem with a new kernel which has otime support in the future.
The reserved bytes are also not zeroed, and we'll have compatibility
issue if we make use of those bytes.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Inodes always allocate free space with BTRFS_BLOCK_GROUP_DATA type,
which means every inode has the same BTRFS_I(inode)->free_space pointer.
This shrinks struct btrfs_inode by 4 bytes (or 8 bytes on 64 bits).
Signed-off-by: Li Zefan <lizefan@huawei.com>
When calling btrfs_next_old_leaf, we were leaking an extent buffer in the
rare case of using the deadlock avoidance code needed for the tree mod log.
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
If a block group is ro, do not count its entries in when we dump space info.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Block group has ro attributes, make dump_space_info show it.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Here is the whole story:
1)
A free space cache consists of two parts:
o free space cache inode, which is special becase it's stored in root tree.
o free space info, which is stored as the above inode's file data.
But we only build up another new inode and does not flush its free space info
onto disk when we _clear and setup_ free space cache, and this ends up with
that the block group cache's cache_state remains DC_SETUP instead of DC_WRITTEN.
And holding DC_SETUP means that we will not truncate this free space cache inode,
which means the disk offset of its file extent will remain _unchanged_ at least
until next transaction finishes committing itself.
2)
We can set a block group readonly when we relocate the block group.
However,
if the readonly block group covers the disk offset where our free space cache
inode is going to write, it will force the free space cache inode into
cow_file_range() and it'll end up hitting a BUG_ON.
3)
Due to the above analysis, we fix this bug by adding the missing dirty flag.
4)
However, it's not over, there is still another case, nospace_cache.
With nospace_cache, we do not want to set dirty flag, instead we just truncate
free space cache inode and bail out with setting cache state DC_WRITTEN.
We can benifit from it since it saves us another 'pre-allocation' part which
usually costs a lot.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
During disk balance, we prealloc new file extent for file data relocation,
but we may fail in 'no available space' case, and it leads to flipping btrfs
into readonly.
It is not necessary to bail out and abort transaction since we do have several
ways to rescue ourselves from ENOSPC case.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Since root can be fetched via BTRFS_I macro directly, we can save an args
for btrfs_is_free_space_inode().
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
For btree inode, its root is also 'tree root', so btree inode can be
misunderstood as a free space inode.
We should add one more check for btree inode.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
From btree_read_extent_buffer_pages(), currently repair_io_failure()
can be called with mirror_num being zero when submit_one_bio() returned
an error before. This used to cause a BUG_ON(!mirror_num) in
repair_io_failure() and indeed this is not a case that needs the I/O
repair code to rewrite disk blocks.
This commit prevents calling repair_io_failure() in this case and thus
avoids the BUG_ON() and malfunction.
Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
So shrink_delalloc has grown all sorts of cruft over the years thanks to
many reworkings of how we track enospc. What happens now as we fill up the
disk is we will loop for freaking ever hoping to reclaim a arbitrary amount
of space of metadata, this was from when everybody flushed at the same time.
Now we only have people flushing one at a time. So instead of trying to
reclaim a huge amount of space, just try to flush a decent chunk of space,
and stop looping as soon as we have enough free space to satisfy our
reservation. This makes xfstests 224 go much faster. Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
$ mkfs.btrfs /dev/sdb7
$ btrfstune -S1 /dev/sdb7
$ mount /dev/sdb7 /mnt/btrfs
mount: block device /dev/sdb7 is write-protected, mounting read-only
$ btrfs dev add /dev/sdb8 /mnt/btrfs/
Now we get a btrfs in which mnt flags has readonly but sb flags does
not. So for those ioctls that only check sb flags with MS_RDONLY, it
is going to be a problem.
Setting subvolume flags is such an ioctl, we should use mnt_want_write_file()
to check RO flags.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
mnt_want_write() and mnt_want_write_file() will check sb->s_flags with
MS_RDONLY, and we don't need to do it ourselves.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Move check of write access to mount into upper functions so that we can
use mnt_want_write_file instead, which is faster than mnt_want_write.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
There is weird logic I had to put in place to make sure that when we were
adding csums that we'd used the delalloc block rsv instead of the global
block rsv. Part of this meant that we had to free up our transaction
reservation before we ran the delayed refs since csum deletion happens
during the delayed ref work. The problem with this is that when we release
a reservation we will add it to the global reserve if it is not full in
order to keep us going along longer before we have to force a transaction
commit. By releasing our reservation before we run delayed refs we don't
get the opportunity to drain down the global reserve for the work we did, so
we won't refill it as often. This isn't a problem per-se, it just results
in us possibly committing transactions more and more often, and in rare
cases could cause those WARN_ON()'s to pop in use_block_rsv because we ran
out of space in our block rsv.
This also helps us by holding onto space while the delayed refs run so we
don't end up with as many people trying to do things at the same time, which
again will help us not force commits or hit the use_block_rsv warnings.
Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
We didn't check error of btrfs_update_inode(), but that error looks
easy to bubble back up.
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
We dereferenced "node" in the error message after freeing it. Also
btrfs_panic() can return so we should return an error code instead of
continuing.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
There used to be a BUG_ON(ret) there before EH patch (79787eaa) went in.
Bail out with EINVAL.
Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This will be used in conjunction with btrfs device ready <dev>. This is
needed for initrd's to have a nice and lightweight way to tell if all of the
devices needed for a file system are in the cache currently. This keeps
them from having to do mount+sleep loops waiting for devices to show up.
Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
