block: Implement zone append emulation

Given that zone write plugging manages all writes to zones of a zoned
block device and tracks the write pointer position of all zones that are
not full nor empty, emulating zone append operations using regular
writes can be implemented generically, without relying on the underlying
device driver to implement such emulation. This is needed for devices
that do not natively support the zone append command (e.g. SMR
hard-disks).

A device may request zone append emulation by setting its
max_zone_append_sectors queue limit to 0. For such device, the function
blk_zone_wplug_prepare_bio() changes zone append BIOs into
non-mergeable regular write BIOs. Modified zone append BIOs are flagged
with the new BIO flag BIO_EMULATES_ZONE_APPEND. This flag is checked
on completion of the BIO in blk_zone_write_plug_bio_endio() to restore
the original REQ_OP_ZONE_APPEND operation code of the BIO.

The block layer internal inline helper function bio_is_zone_append() is
added to test if a BIO is either a native zone append operation
(REQ_OP_ZONE_APPEND operation code) or if it is flagged with
BIO_EMULATES_ZONE_APPEND. Given that both native and emulated zone
append BIO completion handling should be similar, The functions
blk_update_request() and blk_zone_complete_request_bio() are modified to
use bio_is_zone_append() to execute blk_zone_update_request_bio() for
both native and emulated zone append operations.

This commit contains contributions from Christoph Hellwig <hch@lst.de>.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Tested-by: Dennis Maisenbacher <dennis.maisenbacher@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240408014128.205141-11-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 12 insertions, 2 deletions

diff --git a/block/blk.h b/block/blk.h
index 4df969f8fa28..1140c4a0be03 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -421,6 +421,11 @@ static inline bool bio_zone_write_plugging(struct bio *bio)
 {
 	return bio_flagged(bio, BIO_ZONE_WRITE_PLUGGING);
 }
+static inline bool bio_is_zone_append(struct bio *bio)
+{
+	return bio_op(bio) == REQ_OP_ZONE_APPEND ||
+		bio_flagged(bio, BIO_EMULATES_ZONE_APPEND);
+}
 void blk_zone_write_plug_bio_merged(struct bio *bio);
 void blk_zone_write_plug_attempt_merge(struct request *rq);
 static inline void blk_zone_update_request_bio(struct request *rq,
@@ -430,8 +435,9 @@ static inline void blk_zone_update_request_bio(struct request *rq,
 	 * For zone append requests, the request sector indicates the location
 	 * at which the BIO data was written. Return this value to the BIO
 	 * issuer through the BIO iter sector.
-	 * For plugged zone writes, we need the original BIO sector so
-	 * that blk_zone_write_plug_bio_endio() can lookup the zone write plug.
+	 * For plugged zone writes, which include emulated zone append, we need
+	 * the original BIO sector so that blk_zone_write_plug_bio_endio() can
+	 * lookup the zone write plug.
 	 */
 	if (req_op(rq) == REQ_OP_ZONE_APPEND || bio_zone_write_plugging(bio))
 		bio->bi_iter.bi_sector = rq->__sector;
@@ -468,6 +474,10 @@ static inline bool bio_zone_write_plugging(struct bio *bio)
 {
 	return false;
 }
+static inline bool bio_is_zone_append(struct bio *bio)
+{
+	return false;
+}
 static inline void blk_zone_write_plug_bio_merged(struct bio *bio)
 {
 }