block: Allow zero value of max_zone_append_sectors queue limit

In preparation for adding a generic zone append emulation using zone
write plugging, allow device drivers supporting zoned block device to
set a the max_zone_append_sectors queue limit of a device to 0 to
indicate the lack of native support for zone append operations and that
the block layer should emulate these operations using regular write
operations.

blk_queue_max_zone_append_sectors() is modified to allow passing 0 as
the max_zone_append_sectors argument. The function
queue_max_zone_append_sectors() is also modified to ensure that the
minimum of the max_hw_sectors and chunk_sectors limit is used whenever
the max_zone_append_sectors limit is 0. This minimum is consistent with
the value set for the max_zone_append_sectors limit by the function
blk_validate_zoned_limits() when limits for a queue are validated.

The helper functions queue_emulates_zone_append() and
bdev_emulates_zone_append() are added to test if a queue (or block
device) emulates zone append operations.

In order for blk_revalidate_disk_zones() to accept zoned block devices
relying on zone append emulation, the direct check to the
max_zone_append_sectors queue limit of the disk is replaced by a check
using the value returned by queue_max_zone_append_sectors(). Similarly,
queue_zone_append_max_show() is modified to use the same accessor so
that the sysfs attribute advertizes the non-zero limit that will be
used, regardless if it is for native or emulated commands.

For stacking drivers, a top device should not need to care if the
underlying devices have native or emulated zone append operations.
blk_stack_limits() is thus modified to set the top device
max_zone_append_sectors limit using the new accessor
queue_limits_max_zone_append_sectors(). queue_max_zone_append_sectors()
is modified to use this function as well. Stacking drivers that require
zone append emulation, e.g. dm-crypt, can still request this feature by
calling blk_queue_max_zone_append_sectors() with a 0 limit.

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/20240408014128.205141-10-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 3 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 348b57ca0425..46613bf6a402 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1173,12 +1173,29 @@ static inline unsigned int queue_max_segment_size(const struct request_queue *q)
 	return q->limits.max_segment_size;
 }
 
-static inline unsigned int queue_max_zone_append_sectors(const struct request_queue *q)
+static inline unsigned int queue_limits_max_zone_append_sectors(struct queue_limits *l)
 {
+	unsigned int max_sectors = min(l->chunk_sectors, l->max_hw_sectors);
 
-	const struct queue_limits *l = &q->limits;
+	return min_not_zero(l->max_zone_append_sectors, max_sectors);
+}
+
+static inline unsigned int queue_max_zone_append_sectors(struct request_queue *q)
+{
+	if (!blk_queue_is_zoned(q))
+		return 0;
 
-	return min(l->max_zone_append_sectors, l->max_sectors);
+	return queue_limits_max_zone_append_sectors(&q->limits);
+}
+
+static inline bool queue_emulates_zone_append(struct request_queue *q)
+{
+	return blk_queue_is_zoned(q) && !q->limits.max_zone_append_sectors;
+}
+
+static inline bool bdev_emulates_zone_append(struct block_device *bdev)
+{
+	return queue_emulates_zone_append(bdev_get_queue(bdev));
 }
 
 static inline unsigned int