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Subject[RESEND PATCH 2/2] loop: Better discard support for block devices
Date
If the backing device for a loop device is a block device,
then mirror the discard properties of the underlying block
device into the loop device. While in there, differentiate
between REQ_OP_DISCARD and REQ_OP_WRITE_ZEROES, which are
different for block devices, but which the loop device had
just been lumping together.

This change fixes blktest block/003, and removes an extraneous
error print in block/013 when testing on a loop device backed
by a block device that does not support discard.

Signed-off-by: Evan Green <evgreen@chromium.org>
---

drivers/block/loop.c | 61 +++++++++++++++++++++++++++++---------------
1 file changed, 41 insertions(+), 20 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a1ba555e3b92..8c2b6885db56 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -417,19 +417,14 @@ 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_discard(struct loop_device *lo, struct request *rq,
+ int mode, loff_t pos)
{
- /*
- * 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.
- */
struct file *file = lo->lo_backing_file;
- int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
+ struct request_queue *q = lo->lo_queue;
int ret;

- if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
+ if (!blk_queue_discard(q)) {
ret = -EOPNOTSUPP;
goto out;
}
@@ -602,8 +597,13 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
case REQ_OP_FLUSH:
return lo_req_flush(lo, rq);
case REQ_OP_DISCARD:
+ return lo_discard(lo, rq,
+ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, pos);
+
case REQ_OP_WRITE_ZEROES:
- return lo_discard(lo, rq, pos);
+ return lo_discard(lo, rq,
+ FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE, pos);
+
case REQ_OP_WRITE:
if (lo->transfer)
return lo_write_transfer(lo, rq, pos);
@@ -857,6 +857,25 @@ static void loop_config_discard(struct loop_device *lo)
struct file *file = lo->lo_backing_file;
struct inode *inode = file->f_mapping->host;
struct request_queue *q = lo->lo_queue;
+ struct request_queue *backingq;
+
+ /*
+ * If the backing device is a block device, mirror its discard
+ * capabilities.
+ */
+ if (S_ISBLK(inode->i_mode)) {
+ backingq = bdev_get_queue(inode->i_bdev);
+ blk_queue_max_discard_sectors(q,
+ backingq->limits.max_discard_sectors);
+
+ blk_queue_max_write_zeroes_sectors(q,
+ backingq->limits.max_write_zeroes_sectors);
+
+ q->limits.discard_granularity =
+ backingq->limits.discard_granularity;
+
+ q->limits.discard_alignment =
+ backingq->limits.discard_alignment;

/*
* We use punch hole to reclaim the free space used by the
@@ -864,22 +883,24 @@ static void loop_config_discard(struct loop_device *lo)
* encryption is enabled, because it may give an attacker
* useful information.
*/
- if ((!file->f_op->fallocate) ||
- lo->lo_encrypt_key_size) {
+ } else if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
q->limits.discard_granularity = 0;
q->limits.discard_alignment = 0;
blk_queue_max_discard_sectors(q, 0);
blk_queue_max_write_zeroes_sectors(q, 0);
- blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
- return;
- }

- q->limits.discard_granularity = inode->i_sb->s_blocksize;
- q->limits.discard_alignment = 0;
+ } else {
+ q->limits.discard_granularity = inode->i_sb->s_blocksize;
+ q->limits.discard_alignment = 0;
+
+ blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
+ blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
+ }

- blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
- blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
- blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
+ if (q->limits.max_discard_sectors || q->limits.max_write_zeroes_sectors)
+ blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
+ else
+ blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
}

static void loop_unprepare_queue(struct loop_device *lo)
--
2.20.1
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