From: Filipe Manana <fdman...@suse.com>

Verify that a filesystem check operation (fsck) does not report the
following scenario as an error:

An extent is shared between two inodes, as a result of clone/reflink
operation, and for one of the inodes, lets call it inode A, the extent is
referenced through a file extent item as a prealloc extent, while for the
other inode, call it inode B, the extent is referenced through a regular
file extent item, that is, it was written to. The goal of this test is to
make sure a filesystem check operation will not report "odd csum items"
errors for the prealloc extent at inode A, because this scenario is valid
since the extent was written through inode B and therefore it is expected
to have checksum items in the filesystem's checksum btree for that shared
extent.

Such scenario can be created with the following steps for example:

 mkfs.btrfs -f /dev/sdb
 mount /dev/sdb /mnt

 touch /mnt/foo
 xfs_io -c "falloc 0 256K" /mnt/foo
 sync

 xfs_io -c "pwrite -S 0xab -b 0 256K" /mnt/foo
 touch /mnt/bar
 xfs_io -c "reflink /mnt/foo 0 0 256K" /mnt/bar
 xfs_io -c "fsync" /mnt/bar

 <power fail>
 mount /dev/sdb /mnt
 umount /mnt

This scenario is fixed by the following patch for the filesystem checker:

 "Btrfs-progs: check, fix false error reports for shared prealloc extents"

Signed-off-by: Filipe Manana <fdman...@suse.com>
---
 .../reflinked-prealloc-extents.img.xz              | Bin 0 -> 3244 bytes
 .../030-reflinked-prealloc-extents/test.sh         |  42 +++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 
tests/fsck-tests/030-reflinked-prealloc-extents/reflinked-prealloc-extents.img.xz
 create mode 100755 tests/fsck-tests/030-reflinked-prealloc-extents/test.sh

diff --git 
a/tests/fsck-tests/030-reflinked-prealloc-extents/reflinked-prealloc-extents.img.xz
 
b/tests/fsck-tests/030-reflinked-prealloc-extents/reflinked-prealloc-extents.img.xz
new file mode 100644
index 
0000000000000000000000000000000000000000..8adf0071328806fa6981f6ef225084e517d1bc3e
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diff --git a/tests/fsck-tests/030-reflinked-prealloc-extents/test.sh 
b/tests/fsck-tests/030-reflinked-prealloc-extents/test.sh
new file mode 100755
index 00000000..4d3ef7da
--- /dev/null
+++ b/tests/fsck-tests/030-reflinked-prealloc-extents/test.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+#
+# Verify that a filesystem check operation (fsck) does not report the following
+# scenario as an error:
+#
+# An extent is shared between two inodes, as a result of clone/reflink 
operation,
+# and for one of the inodes, lets call it inode A, the extent is referenced
+# through a file extent item as a prealloc extent, while for the other inode,
+# call it inode B, the extent is referenced through a regular file extent item,
+# that is, it was written to. The goal of this test is to make sure a 
filesystem
+# check operation will not report "odd csum items" errors for the prealloc
+# extent at inode A, because this scenario is valid since the extent was 
written
+# through inode B and therefore it is expected to have checksum items in the
+# filesystem's checksum btree for that shared extent.
+#
+# Such scenario can be created with the following steps for example:
+#
+# mkfs.btrfs -f /dev/sdb
+# mount /dev/sdb /mnt
+#
+# touch /mnt/foo
+# xfs_io -c "falloc 0 256K" /mnt/foo
+# sync
+#
+# xfs_io -c "pwrite -S 0xab -b 0 256K" /mnt/foo
+# touch /mnt/bar
+# xfs_io -c "reflink /mnt/foo 0 0 256K" /mnt/bar
+# xfs_io -c "fsync" /mnt/bar
+#
+# <power fail>
+# mount /dev/sdb /mnt
+# umount /mnt
+
+source "$TEST_TOP/common"
+
+check_prereq btrfs
+
+check_image() {
+       run_check "$TOP/btrfs" check "$1"
+}
+
+check_all_images
-- 
2.11.0

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