Jean-Denis Girard noticed commit c821e7f3 "pass bytes to
btrfs_bio_alloc" (https://patchwork.kernel.org/patch/9763081/)
introduces a regression on 32 bit machines.
When CONFIG_LBDAF is _not_ defined (CONFIG_LBDAF == Support for large
(2TB+) block devices and files) sector_t is 32 bit on 32bit machines.

In the function submit_extent_page, 'sector' (which is sector_t type) is
multiplied by 512 to convert it from sectors to bytes, leading to an
overflow when the disk is bigger than 4GB (!).

I added a cast to u64 to avoid overflow.

Fixes: c821e7f3 ("btrfs: pass bytes to btrfs_bio_alloc")
CC: stable@vger.kernel.org # 4.13+
Signed-off-by: NGoffredo Baroncelli <kreijack@inwind.it>
Tested-by: NJean-Denis Girard <jd.girard@sysnux.pf>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Amir reported a bug discovered by his cleaned up version of my
dm-log-writes xfstests where we were missing csums at certain replay
points.  This is because fsx was doing an msync(), which essentially
fsync()'s a specific range of a file.  We will log all modified extents,
but only search for the checksums in the range we are being asked to
sync.  We cannot simply log the extents in the range we're being asked
because we are logging the inode item as it is currently, which if it
has had a i_size update before the msync means we will miss extents when
replaying.  We could possibly get around this by marking the inode with
the transaction that extended the i_size to see if we have this case,
but this would be racy and we'd have to lock the whole range of the
inode to make sure we didn't have an ordered extent outside of our range
that was in the middle of completing.

Fix this simply by keeping track of the modified extents range and
logging the csums for the entire range of extents that we are logging.
This makes the xfstest pass.
Reported-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

commit 4246a0b6 ("block: add a bi_error field to struct bio")
changed the logic of how dio read endio reports errors.

For single stripe dio read, %bio->bi_status reflects the error before
verifying checksum, and now we're updating it when data block matches
with its checksum, while in the mismatching case, %bio->bi_status is
not updated to relfect that.

When some blocks in a file have been corrupted on disk, reading such a
file ends up with

1) checksum errors are reported in kernel log
2) read(2) returns successfully with some content being 0x01.

In order to fix it, we need to report its checksum mismatch error to
the upper layer (dio layer in this case) as well.

Fixes: 4246a0b6 ("block: add a bi_error field to struct bio")
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reported-by: NGoffredo Baroncelli <kreijack@inwind.it>
Tested-by: NGoffredo Baroncelli <kreijack@inwind.it>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Previously, we were calling del_qgroup_item, and ignoring the return code
resulting in a potential to have divergent in-memory state without an
error. Perhaps, it makes sense to handle this error code, and put the
filesystem into a read only, or similar state.

This patch only adds reporting of the error if the error is fatal,
(any error other than qgroup not found).
Signed-off-by: NSargun Dhillon <sargun@sargun.me>
Reviewed-by: NQu Wenruo <quwenruo.btrfs@gmx.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Currently even if the underlying disk reports failure on IO,
compressed read endio still gets to verify checksum and reports it as
a checksum error.

In fact, if some IO have failed during reading a compressed data
extent , there's no way the checksum could match, therefore, we can
skip that in order to return error quickly to the upper layer.

Please note that we need to do this after recording the failed mirror
index so that read-repair in the upper layer's endio can work
properly.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Tested-by: NPaul Jones <paul@pauljones.id.au>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The kernel oops happens at

kernel BUG at fs/btrfs/extent_io.c:2104!
...
RIP: clean_io_failure+0x263/0x2a0 [btrfs]

It's showing that read-repair code is using an improper mirror index.
This is due to the fact that compression read's endio hasn't recorded
the failed mirror index in %cb->orig_bio.

With this, btrfs's read-repair can work properly on reading compressed
data.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reported-by: NPaul Jones <paul@pauljones.id.au>
Tested-by: NPaul Jones <paul@pauljones.id.au>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This seems to be a leftover of commit cf8cddd3 ("btrfs: don't
abuse REQ_OP_* flags for btrfs_map_block").

It should use btrfs_op() helper to provide one of 'enum btrfs_map_op'
types.

Fixes: cf8cddd3 ("btrfs: don't abuse REQ_OP_* flags for btrfs_map_block")
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NSatoru Takeuchi <satoru.takeuchi@gmail.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

It doesn't make sense to backup tree roots when doing fsync, since
during fsync those tree roots have not been consistent on disk.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NQu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Currently, "btrfs quota enable" would fail after "btrfs quota disable" on
the first time with syslog output "qgroup_rescan_init failed with -22", but
it would succeed on the second time.

When "quota disable" is called, BTRFS_FS_QUOTA_DISABLING flag bit will be
set in fs_info->flags in btrfs_quota_disable(), but it will not be droppd
in btrfs_run_qgroups() (which is called in btrfs_commit_transaction())
because quota_root has already been freed. If "quota enable" is called
after that, both BTRFS_FS_QUOTA_DISABLING and BTRFS_FS_QUOTA_ENABLED flag
would be dropped in the btrfs_run_qgroups() since quota_root is not NULL.
This leads to the failure of "quota enable" on the first time.

BTRFS_FS_QUOTA_DISABLING flag is not used outside of "quota disable"
context and is equivalent to whether quota_root is NULL or not.
btrfs_run_qgroups() checks whether quota_root is NULL or not in the first
place.

So, let's remove BTRFS_FS_QUOTA_DISABLING flag.
Signed-off-by: NTomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_cmp_data_prepare() (almost) always returns 0 i.e. ignoring errors
from gather_extent_pages(). While the pages are freed by
btrfs_cmp_data_free(), cmp->num_pages still has > 0. Then,
btrfs_extent_same() try to access the already freed pages causing faults
(or violates PageLocked assertion).

This patch just return the error as is so that the caller stop the process.
Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com>
Fixes: f4414602 ("btrfs: fix deadlock with extent-same and readpage")
Cc: <stable@vger.kernel.org> # 4.2
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

`btrfs sub set-default` succeeds to set an ID which isn't corresponding to any
fs/file tree. If such the bad ID is set to a filesystem, we can't mount this
filesystem without specifying `subvol` or `subvolid` mount options.

Fixes: 6ef5ed0d ("Btrfs: add ioctl and incompat flag to set the default mount subvol")
Cc: <stable@vger.kernel.org>
Signed-off-by: NSatoru Takeuchi <satoru.takeuchi@gmail.com>
Reviewed-by: NQu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

ENOTSUPP should not be returned to the user program.
 (cf. include/linux/errno.h)
Therefore, EOPNOTSUPP is used instead of ENOTSUPP.
Signed-off-by: NTsutomu Itoh <t-itoh@jp.fujitsu.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

__del_reloc_root should be called before freeing up reloc_root->node.
If not, calling __del_reloc_root() dereference reloc_root->node, causing
the system BUG.

Fixes: 6bdf131f ("Btrfs: don't leak reloc root nodes on error")
Cc: <stable@vger.kernel.org> # 4.9
Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

__endio_write_update_ordered() repeats the search until it reaches the end
of the specified range. This works well with direct IO path, because before
the function is called, it's ensured that there are ordered extents filling
whole the range. It's not the case, however, when it's called from
run_delalloc_range(): it is possible to have error in the midle of the loop
in e.g. run_delalloc_nocow(), so that there exisits the range not covered
by any ordered extents. By cleaning such "uncomplete" range,
__endio_write_update_ordered() stucks at offset where there're no ordered
extents.

Since the ordered extents are created from head to tail, we can stop the
search if there are no offset progress.

Fixes: 52427260 ("btrfs: Handle delalloc error correctly to avoid ordered extent hang")
Cc: <stable@vger.kernel.org> # 4.12
Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: NQu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Commit 52427260 ("btrfs: Handle delalloc error correctly to avoid
ordered extent hang") introduced btrfs_cleanup_ordered_extents() to cleanup
submitted ordered extents. However, it does not clear the ordered bit
(Private2) of corresponding pages. Thus, the following BUG occurs from
free_pages_check_bad() (on btrfs/125 with nospace_cache).

BUG: Bad page state in process btrfs  pfn:3fa787
page:ffffdf2acfe9e1c0 count:0 mapcount:0 mapping:          (null) index:0xd
flags: 0x8000000000002008(uptodate|private_2)
raw: 8000000000002008 0000000000000000 000000000000000d 00000000ffffffff
raw: ffffdf2acf5c1b20 ffffb443802238b0 0000000000000000 0000000000000000
page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
bad because of flags: 0x2000(private_2)

This patch clears the flag same as other places calling
btrfs_dec_test_ordered_pending() for every page in the specified range.

Fixes: 52427260 ("btrfs: Handle delalloc error correctly to avoid ordered extent hang")
Cc: <stable@vger.kernel.org> # 4.12
Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: NQu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs_info->super_copy->{node,sector}size are little-endian, but the ioctl
should return the values in native endianness. Use the cached values in
btrfs_fs_info instead. Found with sparse.

Fixes: 80a773fb ("btrfs: retrieve more info from FS_INFO ioctl")
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

flush_epd_write_bio() sets bio->bi_opf by itself to honor REQ_SYNC,
but it's not needed at all since bio->bi_opf has set up properly in
both __extent_writepage() and write_one_eb(), and in the case of
write_one_eb(), it also sets REQ_META, which we will lose in
flush_epd_write_bio().

This remove this unnecessary bio->bi_opf setting.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This updates btrfs to use the helper wbc_to_write_flags which has been
applied in ext4/xfs/f2fs/block.

Please note that, with this, btrfs's dirty pages written by a
writeback job will carry the flag REQ_BACKGROUND, which is currently
used by writeback-throttle to determine whether it should go to get a
request or wait.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The superblock is also metadata of the filesystem so the relevant IO
should be tagged as such. We also tag it as high priority, as it's the
last block committed for metadata from a given transaction. Any delays
would effectively block the whole transaction, also blocking any other
operation holding the device_list_mutex.
Reviewed-by: NJosef Bacik <jbacik@fb.com>
Reviewed-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Commit 38851cc1 ("Btrfs: implement unlocked dio write") implemented
unlocked dio write, allowing multiple dio writers to write to
non-overlapping, and non-eof-extending regions. In doing so it also
introduced a broken memory barrier. It is broken due to 2 things:

1. Memory barriers _MUST_ always be paired, this is clearly not the case
   here

2. Checkpatch actually produces a warning if a memory barrier is
   introduced that doesn't have a comment explaining how it's being
   paired.

Specifically for inode::i_dio_count that's wrapped inside
inode_dio_begin, there is no explicit barrier semantics attached, so
removing is fine as the atomic is used in common the waiter/wakeup
pattern.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ enhance changelog ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Currently this function is always called with the object id of the root
key of the chunk_tree, which is always BTRFS_CHUNK_TREE_OBJECTID. So
let's subsume it straight into the function itself. No functional
change.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

THe function is always called with chunk_objectid set to
BTRFS_FIRST_CHUNK_TREE_OBJECTID. Let's collapse the parameter in the
function itself. No functional changes.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_del_roots always uses the tree_root.  Let's pass fs_info instead.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Every shared ref has a parent tree block, which can be get from
btrfs_extent_inline_ref_offset().  And the tree block must be aligned
to the nodesize, so we'd know this inline ref is not valid if this
block's bytenr is not aligned to the nodesize, in which case, most
likely the ref type has been misused.

This adds the above mentioned check and also updates
print_extent_item() called by btrfs_print_leaf() to point out the
invalid ref while printing the tree structure.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The BUG_ON() can be triggered when the caller is processing an invalid
extent inline ref, e.g.

a shared data ref is offered instead of an extent data ref, such that
it tries to find a non-existent tree block and then btrfs_search_slot
returns 1 for no such item.

This replaces the BUG_ON() with a WARN() followed by calling
btrfs_print_leaf() to show more details about what's going on and
returning -EINVAL to upper callers.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Now that we have a helper to report invalid value of extent inline ref
type, we need to quit gracefully instead of throwing out a kernel panic.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_print_leaf() is used in btrfs_get_extent_inline_ref_type, so
here we really want to print the invalid value of ref type instead of
causing a kernel panic.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Now that btrfs_get_extent_inline_ref_type() can report if type is a
valid one and all callers can gracefully deal with that, we don't need
to crash here.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since we have a helper which can do sanity check, this converts all
btrfs_extent_inline_ref_type to it.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

An invalid value of extent inline ref type may be read from a
malicious image which may force btrfs to crash.

This adds a helper which does sanity check for the ref type, so we can
know if it's sane, return he type, otherwise return an error.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ minimal tweak const types, causing warnings due to other cleanup patches ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Minor simplification, merge calls to one.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Use proper helpers for 64bit division.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Use proper helpers for 64bit division and then cast to narrower type.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

flush_all_writes is an atomic but does not use the semantics at all,
it's just on/off indicator, we can use bool.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

When changing a file's acl mask, btrfs_set_acl() will first set the
group bits of i_mode to the value of the mask, and only then set the
actual extended attribute representing the new acl.

If the second part fails (due to lack of space, for example) and the
file had no acl attribute to begin with, the system will from now on
assume that the mask permission bits are actual group permission bits,
potentially granting access to the wrong users.

Prevent this by restoring the original mode bits if __btrfs_set_acl
fails.
Signed-off-by: NErnesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

BTRFS_FIRST_CHUNK_TREE_OBJECTIS id the only objectid being used in the
chunk_tree. So remove a variable which is always set to that value and collapse
its usage in callees which are passed this variable. No functional changes
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_make_block_group is always called with chunk_objectid set to
BTRFS_FIRST_CHUNK_TREE_OBJECTID. There's no reason why this behavior will
change anytime soon, so let's remove the argument and decrease the cognitive
load when reading the code path. No functional change
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

There is no need for the extra pair of parentheses, remove it. This
fixes the following warning when building with clang:

fs/btrfs/tree-log.c:3694:10: warning: equality comparison with extraneous
  parentheses [-Wparentheses-equality]
                if ((i == (nr - 1)))
                     ~~^~~~~~~~~~~

Also remove the unnecessary parentheses around the substraction.
Signed-off-by: NMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_alloc_dev_extent currently unconditionally sets the uuid in the
leaf block header the function is working with. This is unnecessary
since this operation is peformed by the core btree handling code
(splitting a node, allocating a new btree block etc). So let's remove
it.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

    This patch provides a band aid to improve the 'out of the box'
behaviour of btrfs for disks that are detected as being an ssd.  In a
general purpose mixed workload scenario, the current ssd mode causes
overallocation of available raw disk space for data, while leaving
behind increasing amounts of unused fragmented free space. This
situation leads to early ENOSPC problems which are harming user
experience and adoption of btrfs as a general purpose filesystem.

This patch modifies the data extent allocation behaviour of the ssd mode
to make it behave identical to nossd mode.  The metadata behaviour and
additional ssd_spread option stay untouched so far.

Recommendations for future development are to reconsider the current
oversimplified nossd / ssd distinction and the broken detection
mechanism based on the rotational attribute in sysfs and provide
experienced users with a more flexible way to choose allocator behaviour
for data and metadata, optimized for certain use cases, while keeping
sane 'out of the box' default settings.  The internals of the current
btrfs code have more potential than what currently gets exposed to the
user to choose from.

    The SSD story...

    In the first year of btrfs development, around early 2008, btrfs
gained a mount option which enables specific functionality for
filesystems on solid state devices. The first occurance of this
functionality is in commit e18e4809, labeled "Add mount -o ssd, which
includes optimizations for seek free storage".

The effect on allocating free space for doing (data) writes is to
'cluster' writes together, writing them out in contiguous space, as
opposed to a 'tetris' way of putting all separate writes into any free
space fragment that fits (which is what the -o nossd behaviour does).

A somewhat simplified explanation of what happens is that, when for
example, the 'cluster' size is set to 2MiB, when we do some writes, the
data allocator will search for a free space block that is 2MiB big, and
put the writes in there. The ssd mode itself might allow a 2MiB cluster
to be composed of multiple free space extents with some existing data in
between, while the additional ssd_spread mount option kills off this
option and requires fully free space.

The idea behind this is (commit 536ac8ae): "The [...] clusters make it
more likely a given IO will completely overwrite the ssd block, so it
doesn't have to do an internal rwm cycle."; ssd block meaning nand erase
block. So, effectively this means applying a "locality based algorithm"
and trying to outsmart the actual ssd.

Since then, various changes have been made to the involved code, but the
basic idea is still present, and gets activated whenever the ssd mount
option is active. This also happens by default, when the rotational flag
as seen at /sys/block/<device>/queue/rotational is set to 0.

    However, there's a number of problems with this approach.

    First, what the optimization is trying to do is outsmart the ssd by
assuming there is a relation between the physical address space of the
block device as seen by btrfs and the actual physical storage of the
ssd, and then adjusting data placement. However, since the introduction
of the Flash Translation Layer (FTL) which is a part of the internal
controller of an ssd, these attempts are futile. The use of good quality
FTL in consumer ssd products might have been limited in 2008, but this
situation has changed drastically soon after that time. Today, even the
flash memory in your automatic cat feeding machine or your grandma's
wheelchair has a full featured one.

Second, the behaviour as described above results in the filesystem being
filled up with badly fragmented free space extents because of relatively
small pieces of space that are freed up by deletes, but not selected
again as part of a 'cluster'. Since the algorithm prefers allocating a
new chunk over going back to tetris mode, the end result is a filesystem
in which all raw space is allocated, but which is composed of
underutilized chunks with a 'shotgun blast' pattern of fragmented free
space. Usually, the next problematic thing that happens is the
filesystem wanting to allocate new space for metadata, which causes the
filesystem to fail in spectacular ways.

Third, the default mount options you get for an ssd ('ssd' mode enabled,
'discard' not enabled), in combination with spreading out writes over
the full address space and ignoring freed up space leads to worst case
behaviour in providing information to the ssd itself, since it will
never learn that all the free space left behind is actually free.  There
are two ways to let an ssd know previously written data does not have to
be preserved, which are sending explicit signals using discard or
fstrim, or by simply overwriting the space with new data.  The worst
case behaviour is the btrfs ssd_spread mount option in combination with
not having discard enabled. It has a side effect of minimizing the reuse
of free space previously written in.

Fourth, the rotational flag in /sys/ does not reliably indicate if the
device is a locally attached ssd. For example, iSCSI or NBD displays as
non-rotational, while a loop device on an ssd shows up as rotational.

The combination of the second and third problem effectively means that
despite all the good intentions, the btrfs ssd mode reliably causes the
ssd hardware and the filesystem structures and performance to be choked
to death. The clickbait version of the title of this story would have
been "Btrfs ssd optimizations considered harmful for ssds".

The current nossd 'tetris' mode (even still without discard) allows a
pattern of overwriting much more previously used space, causing many
more implicit discards to happen because of the overwrite information
the ssd gets. The actual location in the physical address space, as seen
from the point of view of btrfs is irrelevant, because the actual writes
to the low level flash are reordered anyway thanks to the FTL.

    Changes made in the code

1. Make ssd mode data allocation identical to tetris mode, like nossd.
2. Adjust and clean up filesystem mount messages so that we can easily
identify if a kernel has this patch applied or not, when providing
support to end users. Also, make better use of the *_and_info helpers to
only trigger messages on actual state changes.

    Backporting notes

Notes for whoever wants to backport this patch to their 4.9 LTS kernel:
* First apply commit 951e7966 "btrfs: drop the nossd flag when
  remounting with -o ssd", or fixup the differences manually.
* The rest of the conflicts are because of the fs_info refactoring. So,
  for example, instead of using fs_info, it's root->fs_info in
  extent-tree.c
Signed-off-by: NHans van Kranenburg <hans.van.kranenburg@mendix.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>