We didn't have a lock to protect the access to the delalloc inodes list, that is
we might access a empty delalloc inodes list if someone start flushing delalloc
inodes because the delalloc inodes were moved into a other list temporarily.
Fix it by wrapping the access with a lock.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

When we create a snapshot, we just need wait the ordered extents in
the source fs/file root, but because we use the global mutex to protect
this ordered extents list of the source fs/file root to avoid accessing
a empty list, if someone got the mutex to access the ordered extents list
of the other fs/file root, we had to wait.

This patch splits the above global mutex, now every fs/file root has
its own mutex to protect its own list.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

We needn't flush all delalloc inodes when we doesn't get s_umount lock,
or we would make the tasks wait for a long time.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

If the snapshot creation happened after the nocow write but before the dirty
data flush, we would fail to flush the dirty data because of no space.

So we must keep track of when those nocow write operations start and when they
end, if there are nocow writers, the snapshot creators must wait. In order
to implement this function, I introduce btrfs_{start, end}_nocow_write(),
which is similar to mnt_{want,drop}_write().

These two functions are only used for nocow file write operations.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Since the "_struct" suffix is mainly used for distinguish the differnt
btrfs_work between the original and the newly created one,
there is no need using the suffix since all btrfs_workers are changed
into btrfs_workqueue.

Also this patch fixed some codes whose code style is changed due to the
too long "_struct" suffix.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Since all the btrfs_worker is replaced with the newly created
btrfs_workqueue, the old codes can be easily remove.
Signed-off-by: NQuwenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->scrub_* with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->qgroup_rescan_worker with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->delayed_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->fixup_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->readahead_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->cache_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->rmw_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->endio_* workqueues with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Replace the fs_info->submit_workers with the newly created
btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Much like the fs_info->workers, replace the fs_info->submit_workers
use the same btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Much like the fs_info->workers, replace the fs_info->delalloc_workers
use the same btrfs_workqueue.
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

Use the newly created btrfs_workqueue_struct to replace the original
fs_info->workers
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Tested-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

We might commit the log sub-transaction which didn't contain the metadata we
logged. It was because we didn't record the log transid and just select
the current log sub-transaction to commit, but the right one might be
committed by the other task already. Actually, we needn't do anything
and it is safe that we go back directly in this case.

This patch improves the log sync by the above idea. We record the transid
of the log sub-transaction in which we log the metadata, and the transid
of the log sub-transaction we have committed. If the committed transid
is >= the transid we record when logging the metadata, we just go back.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

It is possible that many tasks sync the log tree at the same time, but
only one task can do the sync work, the others will wait for it. But those
wait tasks didn't get the result of the log sync, and returned 0 when they
ended the wait. It caused those tasks skipped the error handle, and the
serious problem was they told the users the file sync succeeded but in
fact they failed.

This patch fixes this problem by introducing a log context structure,
we insert it into the a global list. When the sync fails, we will set
the error number of every log context in the list, then the waiting tasks
get the error number of the log context and handle the error if need.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

The log trans id is initialized to be 0 every time we create a log tree,
and the log tree need be re-created after a new transaction is started,
it means the log trans id is unlikely to be a huge number, so we can use
signed integer instead of unsigned long integer to save a bit space.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

During device replace test, we hit a null pointer deference (It was very easy
to reproduce it by running xfstests' btrfs/011 on the devices with the virtio
scsi driver). There were two bugs that caused this problem:
- We might allocate new chunks on the replaced device after we updated
  the mapping tree. And we forgot to replace the source device in those
  mapping of the new chunks.
- We might get the mapping information which including the source device
  before the mapping information update. And then submit the bio which was
  based on that mapping information after we freed the source device.

For the first bug, we can fix it by doing mapping tree update and source
device remove in the same context of the chunk mutex. The chunk mutex is
used to protect the allocable device list, the above method can avoid
the new chunk allocation, and after we remove the source device, all
the new chunks will be allocated on the new device. So it can fix
the first bug.

For the second bug, we need make sure all flighting bios are finished and
no new bios are produced during we are removing the source device. To fix
this problem, we introduced a global @bio_counter, we not only inc/dec
@bio_counter outsize of map_blocks, but also inc it before submitting bio
and dec @bio_counter when ending bios.

Since Raid56 is a little different and device replace dosen't support raid56
yet, it is not addressed in the patch and I add comments to make sure we will
fix it in the future.
Reported-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: NWang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>

If we truncate an uncompressed inline item, ram_bytes isn't updated to reflect
the new size.  The fixe uses the size directly from the item header when
reading uncompressed inlines, and also fixes truncate to update the
size as it goes.
Reported-by: NJens Axboe <axboe@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>
CC: stable@vger.kernel.org

It is better that the position of the lock is close to the data which is
protected by it, because they may be in the same cache line, we will load
less cache lines when we access them. So we rearrange the members' position
of btrfs_space_info structure to make the lock be closer to the its data.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Reviewed-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

Add noinode_cache mount option for btrfs.

Since inode map cache involves all the btrfs_find_free_ino/return_ino
things and if just trigger the mount_opt,
an inode number get from inode map cache will not returned to inode map
cache.

To keep the find and return inode both in the same behavior,
a new bit in mount_opt, CHANGE_INODE_CACHE, is introduced for this idea.
CHANGE_INODE_CACHE is set/cleared in remounting, and the original
INODE_MAP_CACHE is set/cleared according to CHANGE_INODE_CACHE after a
success transaction.
Since find/return inode is all done between btrfs_start_transaction and
btrfs_commit_transaction, this will keep consistent behavior.

Also noinode_cache mount option will not stop the caching_kthread.

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NQu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

There is a bug that using btrfs_previous_item() to search metadata extent item.
This is because in btrfs_previous_item(), we need type match, however, since
skinny metada was introduced by josef, we may mix this two types. So just
use btrfs_previous_item() is not working right.

To keep btrfs_previous_item() like normal tree search, i introduce another
function btrfs_previous_extent_item().
Signed-off-by: NWang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

On one of our gluster clusters we noticed some pretty big lag spikes.  This
turned out to be because our transaction commit was taking like 3 minutes to
complete.  This is because we have like 30 gigs of metadata, so our global
reserve would end up being the max which is like 512 mb.  So our throttling code
would allow a ridiculous amount of delayed refs to build up and then they'd all
get run at transaction commit time, and for a cold mounted file system that
could take up to 3 minutes to run.  So fix the throttling to be based on both
the size of the global reserve and how long it takes us to run delayed refs.
This patch tracks the time it takes to run delayed refs and then only allows 1
seconds worth of outstanding delayed refs at a time.  This way it will auto-tune
itself from cold cache up to when everything is in memory and it no longer has
to go to disk.  This makes our transaction commits take much less time to run.
Thanks,
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

This change adds infrastructure to allow for generic properties for
inodes. Properties are name/value pairs that can be associated with
inodes for different purposes. They are stored as xattrs with the
prefix "btrfs."

Properties can be inherited - this means when a directory inode has
inheritable properties set, these are added to new inodes created
under that directory. Further, subvolumes can also have properties
associated with them, and they can be inherited from their parent
subvolume. Naturally, directory properties have priority over subvolume
properties (in practice a subvolume property is just a regular
property associated with the root inode, objectid 256, of the
subvolume's fs tree).

This change also adds one specific property implementation, named
"compression", whose values can be "lzo" or "zlib" and it's an
inheritable property.

The corresponding changes to btrfs-progs were also implemented.
A patch with xfstests for this feature will follow once there's
agreement on this change/feature.

Further, the script at the bottom of this commit message was used to
do some benchmarks to measure any performance penalties of this feature.

Basically the tests correspond to:

Test 1 - create a filesystem and mount it with compress-force=lzo,
then sequentially create N files of 64Kb each, measure how long it took
to create the files, unmount the filesystem, mount the filesystem and
perform an 'ls -lha' against the test directory holding the N files, and
report the time the command took.

Test 2 - create a filesystem and don't use any compression option when
mounting it - instead set the compression property of the subvolume's
root to 'lzo'. Then create N files of 64Kb, and report the time it took.
The unmount the filesystem, mount it again and perform an 'ls -lha' like
in the former test. This means every single file ends up with a property
(xattr) associated to it.

Test 3 - same as test 2, but uses 4 properties - 3 are duplicates of the
compression property, have no real effect other than adding more work
when inheriting properties and taking more btree leaf space.

Test 4 - same as test 3 but with 10 properties per file.

Results (in seconds, and averages of 5 runs each), for different N
numbers of files follow.

* Without properties (test 1)

                    file creation time        ls -lha time
10 000 files              3.49                   0.76
100 000 files            47.19                   8.37
1 000 000 files         518.51                 107.06

* With 1 property (compression property set to lzo - test 2)

                    file creation time        ls -lha time
10 000 files              3.63                    0.93
100 000 files            48.56                    9.74
1 000 000 files         537.72                  125.11

* With 4 properties (test 3)

                    file creation time        ls -lha time
10 000 files              3.94                    1.20
100 000 files            52.14                   11.48
1 000 000 files         572.70                  142.13

* With 10 properties (test 4)

                    file creation time        ls -lha time
10 000 files              4.61                    1.35
100 000 files            58.86                   13.83
1 000 000 files         656.01                  177.61

The increased latencies with properties are essencialy because of:

*) When creating an inode, we now synchronously write 1 more item
   (an xattr item) for each property inherited from the parent dir
   (or subvolume). This could be done in an asynchronous way such
   as we do for dir intex items (delayed-inode.c), which could help
   reduce the file creation latency;

*) With properties, we now have larger fs trees. For this particular
   test each xattr item uses 75 bytes of leaf space in the fs tree.
   This could be less by using a new item for xattr items, instead of
   the current btrfs_dir_item, since we could cut the 'location' and
   'type' fields (saving 18 bytes) and maybe 'transid' too (saving a
   total of 26 bytes per xattr item) from the btrfs_dir_item type.

Also tried batching the xattr insertions (ignoring proper hash
collision handling, since it didn't exist) when creating files that
inherit properties from their parent inode/subvolume, but the end
results were (surprisingly) essentially the same.

Test script:

$ cat test.pl
  #!/usr/bin/perl -w

  use strict;
  use Time::HiRes qw(time);
  use constant NUM_FILES => 10_000;
  use constant FILE_SIZES => (64 * 1024);
  use constant DEV => '/dev/sdb4';
  use constant MNT_POINT => '/home/fdmanana/btrfs-tests/dev';
  use constant TEST_DIR => (MNT_POINT . '/testdir');

  system("mkfs.btrfs", "-l", "16384", "-f", DEV) == 0 or die "mkfs.btrfs failed!";

  # following line for testing without properties
  #system("mount", "-o", "compress-force=lzo", DEV, MNT_POINT) == 0 or die "mount failed!";

  # following 2 lines for testing with properties
  system("mount", DEV, MNT_POINT) == 0 or die "mount failed!";
  system("btrfs", "prop", "set", MNT_POINT, "compression", "lzo") == 0 or die "set prop failed!";

  system("mkdir", TEST_DIR) == 0 or die "mkdir failed!";
  my ($t1, $t2);

  $t1 = time();
  for (my $i = 1; $i <= NUM_FILES; $i++) {
      my $p = TEST_DIR . '/file_' . $i;
      open(my $f, '>', $p) or die "Error opening file!";
      $f->autoflush(1);
      for (my $j = 0; $j < FILE_SIZES; $j += 4096) {
          print $f ('A' x 4096) or die "Error writing to file!";
      }
      close($f);
  }
  $t2 = time();
  print "Time to create " . NUM_FILES . ": " . ($t2 - $t1) . " seconds.\n";
  system("umount", DEV) == 0 or die "umount failed!";
  system("mount", DEV, MNT_POINT) == 0 or die "mount failed!";

  $t1 = time();
  system("bash -c 'ls -lha " . TEST_DIR . " > /dev/null'") == 0 or die "ls failed!";
  $t2 = time();
  print "Time to ls -lha all files: " . ($t2 - $t1) . " seconds.\n";
  system("umount", DEV) == 0 or die "umount failed!";
Signed-off-by: NFilipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

When writing to a file we drop existing file extent items that cover the
write range and then add a new file extent item that represents that write
range.

Before this change we were doing a tree lookup to remove the file extent
items, and then after we did another tree lookup to insert the new file
extent item.
Most of the time all the file extent items we need to drop are located
within a single leaf - this is the leaf where our new file extent item ends
up at. Therefore, in this common case just combine these 2 operations into
a single one.

By avoiding the second btree navigation for insertion of the new file extent
item, we reduce btree node/leaf lock acquisitions/releases, btree block/leaf
COW operations, CPU time on btree node/leaf key binary searches, etc.

Besides for file writes, this is an operation that happens for file fsync's
as well. However log btrees are much less likely to big as big as regular
fs btrees, therefore the impact of this change is smaller.

The following benchmark was performed against an SSD drive and a
HDD drive, both for random and sequential writes:

  sysbench --test=fileio --file-num=4096 --file-total-size=8G \
     --file-test-mode=[rndwr|seqwr] --num-threads=512 \
     --file-block-size=8192 \ --max-requests=1000000 \
     --file-fsync-freq=0 --file-io-mode=sync [prepare|run]

All results below are averages of 10 runs of the respective test.

** SSD sequential writes

Before this change: 225.88 Mb/sec
After this change:  277.26 Mb/sec

** SSD random writes

Before this change: 49.91 Mb/sec
After this change:  56.39 Mb/sec

** HDD sequential writes

Before this change: 68.53 Mb/sec
After this change:  69.87 Mb/sec

** HDD random writes

Before this change: 13.04 Mb/sec
After this change:  14.39 Mb/sec
Signed-off-by: NFilipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

Convert all applicable cases of printk and pr_* to the btrfs_* macros.

Fix all uses of the BTRFS prefix.
Signed-off-by: NFrank Holton <fholton@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

All the subvolues that are involved in send must be read-only during the
whole operation. The ioctl SUBVOL_SETFLAGS could be used to change the
status to read-write and the result of send stream is undefined if the
data change unexpectedly.

Fix that by adding a refcount for all involved roots and verify that
there's no send in progress during SUBVOL_SETFLAGS ioctl call that does
read-only -> read-write transition.

We need refcounts because there are no restrictions on number of send
parallel operations currently run on a single subvolume, be it source,
parent or one of the multiple clone sources.

Kernel is silent when the RO checks fail and returns EPERM. The same set
of checks is done already in userspace before send starts.
Signed-off-by: NDavid Sterba <dsterba@suse.cz>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

It's not used anywhere, so just drop it.
Signed-off-by: NFilipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

I need to create a fake tree to test qgroups and I don't want to have to setup a
fake btree_inode.  The fact is we only use the radix tree for the fs_info, so
everybody else who allocates an extent_io_tree is just wasting the space anyway.
This patch moves the radix tree and its lock into btrfs_fs_info so there is less
stuff I have to fake to do qgroup sanity tests.  Thanks,
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

The kernel macro pr_debug is defined as a empty statement when DEBUG is
not defined. Make btrfs_debug match pr_debug to avoid spamming
the kernel log with debug messages
Signed-off-by: NFrank Holton <fholton@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

Found by uselex.rb:
> btrfs_get_inode_ref_index: [R]: exported from:
fs/btrfs/inode-item.o fs/btrfs/btrfs.o fs/btrfs/built-in.o
Signed-off-by: NSergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: NDavid Stebra <dsterba@suse.cz>
Signed-off-by: NWang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

There are many btrfs functions that manually search the tree for an
item. They all reimplement the same mechanism and differ in the
conditions that they use to find the item. __inode_info() is one such
example. Zach Brown proposed creating a new interface to take the place
of these functions.

This patch is the first step to creating the interface. A new function,
btrfs_find_item, has been added to ctree.c and prototyped in ctree.h.
It is identical to __inode_info, except that the order of the parameters
has been rearranged to more closely those of similar functions elsewhere
in the code (now, root and path come first, then the objectid, offset
and type, and the key to be filled in last). __inode_info's callers have
been set to call this new function instead, and __inode_info itself has
been removed.
Signed-off-by: NKelley Nielsen <kelleynnn@gmail.com>
Suggested-by: NZach Brown <zab@redhat.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

Now that we have the infrastructure for per-super attributes, we can
publish device membership in /sys/fs/btrfs/<fsid>/devices. The information
is published as symlinks to the block devices.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

While trying to debug ENOSPC issues, it's helpful to understand what the
kernel's view of the available space is. We export this information
via ioctl, but sysfs files are more easily used.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

This patch adds per-super attributes to sysfs.

It doesn't publish any attributes yet, but does the proper lifetime
handling as well as the basic infrastructure to add new attributes.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>

There are some feature bits that require no offline setup and can
be enabled online. I've only reviewed extended irefs, but there will
probably be more.

We introduce three new ioctls:
- BTRFS_IOC_GET_SUPPORTED_FEATURES: query the kernel for supported features.
- BTRFS_IOC_GET_FEATURES: query the kernel for enabled features on a per-fs
  basis, as well as querying for which features are changeable with mounted.
- BTRFS_IOC_SET_FEATURES: change features on a per-fs basis.

We introduce two new masks per feature set (_SAFE_SET and _SAFE_CLEAR) that
allow us to define which features are safe to change at runtime.

The failure modes for BTRFS_IOC_SET_FEATURES are as follows:
- Enabling a completely unsupported feature: warns and returns -ENOTSUPP
- Enabling a feature that can only be done offline: warns and returns -EPERM
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <clm@fb.com>