[PATCH] loop: change to punch hole if zero range is not supported

[Shijie Luo <luoshijie1@huawei.com>]

We found a problem when excuting these operations.

$ cd /tmp
$ qemu-img create -f raw test.img 10G
$ mknod -m 0660 /dev/loop0 b 7 0
$ losetup /dev/loop0 test.img
$ mkfs /dev/loop0

Here is the error message.

[  142.364823] blk_update_request: operation not supported error,
 dev loop0, sector 20971392 op 0x9:(WRITE_ZEROES) flags 0x1000800
 phys_seg 0 prio class 0
[  142.371823] blk_update_request: operation not supported error,
 dev loop0, sector 5144 op 0x9:(WRITE_ZEROES) flags 0x1000800
 phys_seg 0 prio class 0

The problem is that not all filesystem support zero range (eg, tmpfs), if
 filesystem doesn 't support zero range, change to punch hole to fix it.

Fixes: efcfec579f613 ("loop: fix no-unmap write-zeroes request behavior")
Signed-off-by: Shijie Luo <luoshijie1@huawei.com>
---
 drivers/block/loop.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index c33bbbfd1bd9..504e658adcaf 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -450,6 +450,13 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 	}
 
 	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
+
+	if ((ret == -EOPNOTSUPP) && (mode & FALLOC_FL_ZERO_RANGE)) {
+		mode &= ~FALLOC_FL_ZERO_RANGE;
+		mode |= FALLOC_FL_PUNCH_HOLE;
+		ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
+	}
+
 	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
 		ret = -EIO;
  out:
-- 
2.19.1