Add 'discard' request handling
Some block devices benefit from a hint that they can forget the contents
of certain sectors. Add basic support for this to the block core, along
with a 'blkdev_issue_discard()' helper function which issues such
requests.
The caller doesn't get to provide an end_io functio, since
blkdev_issue_discard() will automatically split the request up into
multiple bios if appropriate. Neither does the function wait for
completion -- it's expected that callers won't care about when, or even
_if_, the request completes. It's only a hint to the device anyway. By
definition, the file system doesn't _care_ about these sectors any more.
[With feedback from OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> and
Jens Axboe <jens.axboe@oracle.com]
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index a09ead1..273121c 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -315,3 +315,72 @@
return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
+
+static void blkdev_discard_end_io(struct bio *bio, int err)
+{
+ if (err) {
+ if (err == -EOPNOTSUPP)
+ set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
+ clear_bit(BIO_UPTODATE, &bio->bi_flags);
+ }
+
+ bio_put(bio);
+}
+
+/**
+ * blkdev_issue_discard - queue a discard
+ * @bdev: blockdev to issue discard for
+ * @sector: start sector
+ * @nr_sects: number of sectors to discard
+ *
+ * Description:
+ * Issue a discard request for the sectors in question. Does not wait.
+ */
+int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
+ unsigned nr_sects)
+{
+ struct request_queue *q;
+ struct bio *bio;
+ int ret = 0;
+
+ if (bdev->bd_disk == NULL)
+ return -ENXIO;
+
+ q = bdev_get_queue(bdev);
+ if (!q)
+ return -ENXIO;
+
+ if (!q->prepare_discard_fn)
+ return -EOPNOTSUPP;
+
+ while (nr_sects && !ret) {
+ bio = bio_alloc(GFP_KERNEL, 0);
+ if (!bio)
+ return -ENOMEM;
+
+ bio->bi_end_io = blkdev_discard_end_io;
+ bio->bi_bdev = bdev;
+
+ bio->bi_sector = sector;
+
+ if (nr_sects > q->max_hw_sectors) {
+ bio->bi_size = q->max_hw_sectors << 9;
+ nr_sects -= q->max_hw_sectors;
+ sector += q->max_hw_sectors;
+ } else {
+ bio->bi_size = nr_sects << 9;
+ nr_sects = 0;
+ }
+ bio_get(bio);
+ submit_bio(WRITE_DISCARD, bio);
+
+ /* Check if it failed immediately */
+ if (bio_flagged(bio, BIO_EOPNOTSUPP))
+ ret = -EOPNOTSUPP;
+ else if (!bio_flagged(bio, BIO_UPTODATE))
+ ret = -EIO;
+ bio_put(bio);
+ }
+ return ret;
+}
+EXPORT_SYMBOL(blkdev_issue_discard);
diff --git a/block/blk-core.c b/block/blk-core.c
index a496727..1e143c4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1079,6 +1079,10 @@
*/
if (unlikely(bio_barrier(bio)))
req->cmd_flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+ if (unlikely(bio_discard(bio))) {
+ req->cmd_flags |= (REQ_SOFTBARRIER | REQ_DISCARD);
+ req->q->prepare_discard_fn(req->q, req);
+ }
if (bio_sync(bio))
req->cmd_flags |= REQ_RW_SYNC;
@@ -1095,7 +1099,7 @@
static int __make_request(struct request_queue *q, struct bio *bio)
{
struct request *req;
- int el_ret, nr_sectors, barrier, err;
+ int el_ret, nr_sectors, barrier, discard, err;
const unsigned short prio = bio_prio(bio);
const int sync = bio_sync(bio);
int rw_flags;
@@ -1115,6 +1119,12 @@
goto end_io;
}
+ discard = bio_discard(bio);
+ if (unlikely(discard) && !q->prepare_discard_fn) {
+ err = -EOPNOTSUPP;
+ goto end_io;
+ }
+
spin_lock_irq(q->queue_lock);
if (unlikely(barrier) || elv_queue_empty(q))
@@ -1405,7 +1415,8 @@
if (bio_check_eod(bio, nr_sectors))
goto end_io;
- if (bio_empty_barrier(bio) && !q->prepare_flush_fn) {
+ if ((bio_empty_barrier(bio) && !q->prepare_flush_fn) ||
+ (bio_discard(bio) && !q->prepare_discard_fn)) {
err = -EOPNOTSUPP;
goto end_io;
}
@@ -1487,7 +1498,6 @@
* go through the normal accounting stuff before submission.
*/
if (bio_has_data(bio)) {
-
if (rw & WRITE) {
count_vm_events(PGPGOUT, count);
} else {
@@ -1881,7 +1891,7 @@
struct request_queue *q = rq->q;
unsigned long flags = 0UL;
- if (bio_has_data(rq->bio)) {
+ if (bio_has_data(rq->bio) || blk_discard_rq(rq)) {
if (__end_that_request_first(rq, error, nr_bytes))
return 1;
@@ -1939,7 +1949,7 @@
**/
int __blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
{
- if (bio_has_data(rq->bio) &&
+ if ((bio_has_data(rq->bio) || blk_discard_rq(rq)) &&
__end_that_request_first(rq, error, nr_bytes))
return 1;
@@ -2012,12 +2022,14 @@
we want BIO_RW_AHEAD (bit 1) to imply REQ_FAILFAST (bit 1). */
rq->cmd_flags |= (bio->bi_rw & 3);
- rq->nr_phys_segments = bio_phys_segments(q, bio);
- rq->nr_hw_segments = bio_hw_segments(q, bio);
+ if (bio_has_data(bio)) {
+ rq->nr_phys_segments = bio_phys_segments(q, bio);
+ rq->nr_hw_segments = bio_hw_segments(q, bio);
+ rq->buffer = bio_data(bio);
+ }
rq->current_nr_sectors = bio_cur_sectors(bio);
rq->hard_cur_sectors = rq->current_nr_sectors;
rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
- rq->buffer = bio_data(bio);
rq->data_len = bio->bi_size;
rq->bio = rq->biotail = bio;
diff --git a/block/blk-settings.c b/block/blk-settings.c
index dfc7701..539d873 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -33,6 +33,23 @@
EXPORT_SYMBOL(blk_queue_prep_rq);
/**
+ * blk_queue_set_discard - set a discard_sectors function for queue
+ * @q: queue
+ * @dfn: prepare_discard function
+ *
+ * It's possible for a queue to register a discard callback which is used
+ * to transform a discard request into the appropriate type for the
+ * hardware. If none is registered, then discard requests are failed
+ * with %EOPNOTSUPP.
+ *
+ */
+void blk_queue_set_discard(struct request_queue *q, prepare_discard_fn *dfn)
+{
+ q->prepare_discard_fn = dfn;
+}
+EXPORT_SYMBOL(blk_queue_set_discard);
+
+/**
* blk_queue_merge_bvec - set a merge_bvec function for queue
* @q: queue
* @mbfn: merge_bvec_fn
