btrfs: fix fiemap merging compressed extents

Compressed extents are never supposed to be merged by the fiemap code and
reported as a single extent, as each extent's content comes from a
different compression stream and has its own header and context.

We currently rely on checking the logical and physical address adjacency
to prevent merging compressed extents but that is broken. Consider the
following reproducer which explains why the merging happens:

  $ cat test.sh
  #!/bin/bash

  DEV=/dev/sdi
  MNT=/mnt/sdi

  mkfs.btrfs -s 4K -f $DEV
  mount -o compress $DEV $MNT

  # Do a write that compresses to a single 4K extent and represents the
  # maximum compressed chunk size (128K).
  xfs_io -f -c "pwrite 0 128K" $MNT/foo

  # Sync to flush delalloc and allocate the 4K extent.
  sync -f $MNT

  # Now allocate a 124K extent in some other file, which will be adjacent
  # (to the right) of the 4K extent previously allocated.
  xfs_io -f -c "falloc 0 124K" $MNT/filler

  # Do another write to the main file at its current EOF that is
  # compressible and fits in a 4K extent.
  xfs_io -c "pwrite 128K 128K" $MNT/foo
  # Sync to flush delalloc and allocate the 4K extent.
  sync -f $MNT

  # Run fiemap which should report 2 encoded extents, each with a
  # logical size of 128K.
  xfs_io -c "fiemap -v" $MNT/foo

  umount $MNT

Running this, fiemap will report a single extent:

  $ ./test.sh
  (...)
  /mnt/sdi/foo:
   EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
     0: [0..511]:        26624..27135       512   0x9

Fix this by never attempting to merge extents if the flags contain
FIEMAP_EXTENT_ENCODED.

Fixes: 4751832da990 ("btrfs: fiemap: Cache and merge fiemap extent before submit it to user")
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions