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loop: fix no-unmap write-zeroes request behavior

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Currently, if the loop device receives a WRITE_ZEROES request, it asks
the underlying filesystem to punch out the range.  This behavior is
correct if unmapping is allowed.  However, a NOUNMAP request means that
the caller doesn't want us to free the storage backing the range, so
punching out the range is incorrect behavior.

To satisfy a NOUNMAP | WRITE_ZEROES request, loop should ask the
underlying filesystem to FALLOC_FL_ZERO_RANGE, which is (according to
the fallocate documentation) required to ensure that the entire range is
backed by real storage, which suffices for our purposes.

Fixes: 19372e2769 ("loop: implement REQ_OP_WRITE_ZEROES")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Darrick J. Wong 2019-10-30 20:29:48 -07:00 committed by Jens Axboe
parent a4414aedf4
commit efcfec579f
1 changed files with 18 additions and 8 deletions
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26
drivers/block/loop.c
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@ -417,18 +417,20 @@ static int lo_read_transfer(struct loop_device *lo, struct request *rq,
return ret;
}
static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
int mode)
{
/*
* We use punch hole to reclaim the free space used by the
* image a.k.a. discard. However we do not support discard if
* encryption is enabled, because it may give an attacker
* useful information.
* We use fallocate to manipulate the space mappings used by the image
* a.k.a. discard/zerorange. However we do not support this if
* encryption is enabled, because it may give an attacker useful
* information.
*/
struct file *file = lo->lo_backing_file;
int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
int ret;
mode |= FALLOC_FL_KEEP_SIZE;
if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
ret = -EOPNOTSUPP;
goto out;
@ -596,9 +598,17 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
switch (req_op(rq)) {
case REQ_OP_FLUSH:
return lo_req_flush(lo, rq);
case REQ_OP_DISCARD:
case REQ_OP_WRITE_ZEROES:
return lo_discard(lo, rq, pos);
/*
* If the caller doesn't want deallocation, call zeroout to
* write zeroes the range. Otherwise, punch them out.
*/
return lo_fallocate(lo, rq, pos,
(rq->cmd_flags & REQ_NOUNMAP) ?
FALLOC_FL_ZERO_RANGE :
FALLOC_FL_PUNCH_HOLE);
case REQ_OP_DISCARD:
return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
case REQ_OP_WRITE:
if (lo->transfer)
return lo_write_transfer(lo, rq, pos);