block: Add common atomic writes enable flag

Currently only stacked devices need to explicitly enable atomic writes by
setting BLK_FEAT_ATOMIC_WRITES_STACKED flag.

This does not work well for device mapper stacking devices, as there many
sets of limits are stacked and what is the 'bottom' and 'top' device can
swapped. This means that BLK_FEAT_ATOMIC_WRITES_STACKED needs to be set
for many queue limits, which is messy.

Generalize enabling atomic writes enabling by ensuring that all devices
must explicitly set a flag - that includes NVMe, SCSI sd, and md raid.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/r/20250116170301.474130-2-john.g.garry@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: johnpgarry

block/blk-settings.c

@@ -175,6 +175,9 @@ static void blk_validate_atomic_write_limits(struct queue_limits *lim)
 {
 	unsigned int boundary_sectors;
 
+	if (!(lim->features & BLK_FEAT_ATOMIC_WRITES))
+		goto unsupported;
+
 	if (!lim->atomic_write_hw_max)
 		goto unsupported;
 
@@ -611,7 +614,7 @@ static bool blk_stack_atomic_writes_head(struct queue_limits *t,
 static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 				struct queue_limits *b, sector_t start)
 {
-	if (!(t->features & BLK_FEAT_ATOMIC_WRITES_STACKED))
+	if (!(b->features & BLK_FEAT_ATOMIC_WRITES))
 		goto unsupported;
 
 	if (!b->atomic_write_hw_unit_min)
@@ -639,7 +642,6 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 	t->atomic_write_hw_unit_max = 0;
 	t->atomic_write_hw_unit_min = 0;
 	t->atomic_write_hw_boundary = 0;
-	t->features &= ~BLK_FEAT_ATOMIC_WRITES_STACKED;
 }
 
 /**

drivers/md/raid0.c

@@ -384,7 +384,7 @@ static int raid0_set_limits(struct mddev *mddev)
 	lim.max_write_zeroes_sectors = mddev->chunk_sectors;
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * mddev->raid_disks;
-	lim.features |= BLK_FEAT_ATOMIC_WRITES_STACKED;
+	lim.features |= BLK_FEAT_ATOMIC_WRITES;
 	err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
 	if (err) {
 		queue_limits_cancel_update(mddev->gendisk->queue);

drivers/md/raid1.c

@@ -3217,7 +3217,7 @@ static int raid1_set_limits(struct mddev *mddev)
 
 	md_init_stacking_limits(&lim);
 	lim.max_write_zeroes_sectors = 0;
-	lim.features |= BLK_FEAT_ATOMIC_WRITES_STACKED;
+	lim.features |= BLK_FEAT_ATOMIC_WRITES;
 	err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
 	if (err) {
 		queue_limits_cancel_update(mddev->gendisk->queue);

drivers/md/raid10.c

@@ -4018,7 +4018,7 @@ static int raid10_set_queue_limits(struct mddev *mddev)
 	lim.max_write_zeroes_sectors = 0;
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * raid10_nr_stripes(conf);
-	lim.features |= BLK_FEAT_ATOMIC_WRITES_STACKED;
+	lim.features |= BLK_FEAT_ATOMIC_WRITES;
 	err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
 	if (err) {
 		queue_limits_cancel_update(mddev->gendisk->queue);

drivers/nvme/host/core.c

@@ -2002,6 +2002,7 @@ static void nvme_update_atomic_write_disk_info(struct nvme_ns *ns,
 	lim->atomic_write_hw_boundary = boundary;
 	lim->atomic_write_hw_unit_min = bs;
 	lim->atomic_write_hw_unit_max = rounddown_pow_of_two(atomic_bs);
+	lim->features |= BLK_FEAT_ATOMIC_WRITES;
 }
 
 static u32 nvme_max_drv_segments(struct nvme_ctrl *ctrl)

drivers/scsi/sd.c

@@ -991,6 +991,7 @@ static void sd_config_atomic(struct scsi_disk *sdkp, struct queue_limits *lim)
 	lim->atomic_write_hw_boundary = 0;
 	lim->atomic_write_hw_unit_min = unit_min * logical_block_size;
 	lim->atomic_write_hw_unit_max = unit_max * logical_block_size;
+	lim->features |= BLK_FEAT_ATOMIC_WRITES;
 }
 
 static blk_status_t sd_setup_write_same16_cmnd(struct scsi_cmnd *cmd,

include/linux/blkdev.h

@@ -331,8 +331,8 @@ typedef unsigned int __bitwise blk_features_t;
 #define BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE \
 	((__force blk_features_t)(1u << 15))
 
-/* stacked device can/does support atomic writes */
-#define BLK_FEAT_ATOMIC_WRITES_STACKED \
+/* atomic writes enabled */
+#define BLK_FEAT_ATOMIC_WRITES \
 	((__force blk_features_t)(1u << 16))
 
 /*