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Commit 4e004c31 authored by Darrick J. Wong's avatar Darrick J. Wong Committed by Greg Kroah-Hartman
Browse files

loop: fix no-unmap write-zeroes request behavior 



[ Upstream commit efcfec579f6139528c9e6925eca2bc4a36da65c6 ]

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: 19372e27 ("loop: implement REQ_OP_WRITE_ZEROES")
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent c2c58029

drivers/block/loop.c

+18 −8
Original line number Diff line number Diff line
@@ -416,18 +416,20 @@ 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);