From: Miao Xie on
we cannot use the loop device which has been connected to a file in the btrf

The reproduce steps is following:
# dd if=/dev/zero of=vdev0 bs=1M count=1024
# losetup /dev/loop0 vdev0
# mkfs.btrfs /dev/loop0
failed to zero device start -5

The reason is that the btrfs don't implement either ->write_begin or ->write
the VFS API, so we fix it by setting ->write to do_sync_write().

Signed-off-by: Miao Xie <miaox(a)>
fs/btrfs/file.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 79437c5..abcb918 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1197,6 +1197,7 @@ static int btrfs_file_mmap(struct file *filp, struct vm_area_struct *vma)
const struct file_operations btrfs_file_operations = {
.llseek = generic_file_llseek,
.read = do_sync_read,
+ .write = do_sync_write,
.aio_read = generic_file_aio_read,
.splice_read = generic_file_splice_read,
.aio_write = btrfs_file_aio_write,

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