From 259072b7a1c20f8612dcaa8e0e027004aa98f864 Mon Sep 17 00:00:00 2001

From: Filipe Manana <fdmanana@suse.com>

Date: Wed, 6 Jan 2016 22:42:35 +0000

Subject: [PATCH 2/2] Btrfs: fix fitrim discarding device area reserved for

 boot loader's use

As of the 4.3 kernel release, the fitrim ioctl can now discard any region

of a disk that is not allocated to any chunk/block group, including the

first megabyte which is used for our primary superblock and by the boot

loader (grub for example).

Fix this by not allowing to trim/discard any region in the device starting

with an offset not greater than min(alloc_start_mount_option, 1Mb), just

as it was not possible before 4.3.

A reproducer test case for xfstests follows.

  seq=`basename $0`

  seqres=$RESULT_DIR/$seq

  echo "QA output created by $seq"

  tmp=/tmp/$$

  status=1	# failure is the default!

  trap "_cleanup; exit \$status" 0 1 2 3 15

  _cleanup()

  {

      cd /

      rm -f $tmp.*

  }

  # get standard environment, filters and checks

  . ./common/rc

  . ./common/filter

  # real QA test starts here

  _need_to_be_root

  _supported_fs btrfs

  _supported_os Linux

  _require_scratch

  rm -f $seqres.full

  _scratch_mkfs >>$seqres.full 2>&1

  # Write to the [0, 64Kb[ and [68Kb, 1Mb[ ranges of the device. These ranges are

  # reserved for a boot loader to use (GRUB for example) and btrfs should never

  # use them - neither for allocating metadata/data nor should trim/discard them.

  # The range [64Kb, 68Kb[ is used for the primary superblock of the filesystem.

  $XFS_IO_PROG -c "pwrite -S 0xfd 0 64K" $SCRATCH_DEV | _filter_xfs_io

  $XFS_IO_PROG -c "pwrite -S 0xfd 68K 956K" $SCRATCH_DEV | _filter_xfs_io

  # Now mount the filesystem and perform a fitrim against it.

  _scratch_mount

  _require_batched_discard $SCRATCH_MNT

  $FSTRIM_PROG $SCRATCH_MNT

  # Now unmount the filesystem and verify the content of the ranges was not

  # modified (no trim/discard happened on them).

  _scratch_unmount

  echo "Content of the ranges [0, 64Kb] and [68Kb, 1Mb[ after fitrim:"

  od -t x1 -N $((64 * 1024)) $SCRATCH_DEV

  od -t x1 -j $((68 * 1024)) -N $((956 * 1024)) $SCRATCH_DEV

  status=0

  exit

Reported-by: Vincent Petry  <PVince81@yahoo.fr>

Reported-by: Andrei Borzenkov <arvidjaar@gmail.com>

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109341

Fixes: 499f377f49f0 (btrfs: iterate over unused chunk space in FITRIM)

Cc: stable@vger.kernel.org # 4.3+

Signed-off-by: Filipe Manana <fdmanana@suse.com>

---

 fs/btrfs/volumes.c | 20 ++++++++++----------

 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c

index b816b3a2e118..96f8c827d563 100644

--- a/fs/btrfs/volumes.c

+++ b/fs/btrfs/volumes.c

@@ -1208,6 +1208,15 @@ int find_free_dev_extent_start(struct btrfs_transaction *transaction,

 	int ret;

 	int slot;

 	struct extent_buffer *l;

+	u64 min_search_start;

+

+	/*

+	 * We don't want to overwrite the superblock on the drive nor any area

+	 * used by the boot loader (grub for example), so we make sure to start

+	 * at an offset of at least 1MB.

+	 */

+	min_search_start = max(root->fs_info->alloc_start, 1024ull * 1024);

+	search_start = max(search_start, min_search_start);

 	path = btrfs_alloc_path();

 	if (!path)

@@ -1348,18 +1357,9 @@ int find_free_dev_extent(struct btrfs_trans_handle *trans,

 			 struct btrfs_device *device, u64 num_bytes,

 			 u64 *start, u64 *len)

 {

-	struct btrfs_root *root = device->dev_root;

-	u64 search_start;

-

 	/* FIXME use last free of some kind */

-

-	/*

-	 * we don't want to overwrite the superblock on the drive,

-	 * so we make sure to start at an offset of at least 1MB

-	 */

-	search_start = max(root->fs_info->alloc_start, 1024ull * 1024);

 	return find_free_dev_extent_start(trans->transaction, device,

-					  num_bytes, search_start, start, len);

+					  num_bytes, 0, start, len);

 }

 static int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,

-- 

2.5.0