block: move the dax flag to queue_limits

Move the dax flag into the queue_limits feature field so that it can be
set atomically with the queue frozen.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20240617060532.127975-21-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/blk-mq-debugfs.c

@@ -88,7 +88,6 @@ static const char *const blk_queue_flag_name[] = {
 	QUEUE_FLAG_NAME(SAME_FORCE),
 	QUEUE_FLAG_NAME(INIT_DONE),
 	QUEUE_FLAG_NAME(POLL),
-	QUEUE_FLAG_NAME(DAX),
 	QUEUE_FLAG_NAME(STATS),
 	QUEUE_FLAG_NAME(REGISTERED),
 	QUEUE_FLAG_NAME(QUIESCED),

drivers/md/dm-table.c

@@ -1834,11 +1834,11 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 		limits->features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
 
 	if (dm_table_supports_dax(t, device_not_dax_capable)) {
-		blk_queue_flag_set(QUEUE_FLAG_DAX, q);
+		limits->features |= BLK_FEAT_DAX;
 		if (dm_table_supports_dax(t, device_not_dax_synchronous_capable))
 			set_dax_synchronous(t->md->dax_dev);
 	} else
-		blk_queue_flag_clear(QUEUE_FLAG_DAX, q);
+		limits->features &= ~BLK_FEAT_DAX;
 
 	if (dm_table_any_dev_attr(t, device_dax_write_cache_enabled, NULL))
 		dax_write_cache(t->md->dax_dev, true);

drivers/nvdimm/pmem.c

@@ -465,7 +465,6 @@ static int pmem_attach_disk(struct device *dev,
 	struct dax_device *dax_dev;
 	struct nd_pfn_sb *pfn_sb;
 	struct pmem_device *pmem;
-	struct request_queue *q;
 	struct gendisk *disk;
 	void *addr;
 	int rc;
@@ -499,6 +498,8 @@ static int pmem_attach_disk(struct device *dev,
 	}
 	if (fua)
 		lim.features |= BLK_FEAT_FUA;
+	if (is_nd_pfn(dev))
+		lim.features |= BLK_FEAT_DAX;
 
 	if (!devm_request_mem_region(dev, res->start, resource_size(res),
 				dev_name(&ndns->dev))) {
@@ -509,7 +510,6 @@ static int pmem_attach_disk(struct device *dev,
 	disk = blk_alloc_disk(&lim, nid);
 	if (IS_ERR(disk))
 		return PTR_ERR(disk);
-	q = disk->queue;
 
 	pmem->disk = disk;
 	pmem->pgmap.owner = pmem;
@@ -547,9 +547,6 @@ static int pmem_attach_disk(struct device *dev,
 	}
 	pmem->virt_addr = addr;
 
-	if (pmem->pfn_flags & PFN_MAP)
-		blk_queue_flag_set(QUEUE_FLAG_DAX, q);
-
 	disk->fops		= &pmem_fops;
 	disk->private_data	= pmem;
 	nvdimm_namespace_disk_name(ndns, disk->disk_name);

drivers/s390/block/dcssblk.c

@@ -548,6 +548,7 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 {
 	struct queue_limits lim = {
 		.logical_block_size	= 4096,
+		.features		= BLK_FEAT_DAX,
 	};
 	int rc, i, j, num_of_segments;
 	struct dcssblk_dev_info *dev_info;
@@ -643,7 +644,6 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 	dev_info->gd->fops = &dcssblk_devops;
 	dev_info->gd->private_data = dev_info;
 	dev_info->gd->flags |= GENHD_FL_NO_PART;
-	blk_queue_flag_set(QUEUE_FLAG_DAX, dev_info->gd->queue);
 
 	seg_byte_size = (dev_info->end - dev_info->start + 1);
 	set_capacity(dev_info->gd, seg_byte_size >> 9); // size in sectors

include/linux/blkdev.h

@@ -307,6 +307,9 @@ enum {
 
 	/* supports REQ_NOWAIT */
 	BLK_FEAT_NOWAIT				= (1u << 7),
+
+	/* supports DAX */
+	BLK_FEAT_DAX				= (1u << 8),
 };
 
 /*
@@ -575,7 +578,6 @@ struct request_queue {
 #define QUEUE_FLAG_SAME_FORCE	12	/* force complete on same CPU */
 #define QUEUE_FLAG_INIT_DONE	14	/* queue is initialized */
 #define QUEUE_FLAG_POLL		16	/* IO polling enabled if set */
-#define QUEUE_FLAG_DAX		19	/* device supports DAX */
 #define QUEUE_FLAG_STATS	20	/* track IO start and completion times */
 #define QUEUE_FLAG_REGISTERED	22	/* queue has been registered to a disk */
 #define QUEUE_FLAG_QUIESCED	24	/* queue has been quiesced */
@@ -602,7 +604,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 #define blk_queue_io_stat(q)	((q)->limits.features & BLK_FEAT_IO_STAT)
 #define blk_queue_zone_resetall(q)	\
 	test_bit(QUEUE_FLAG_ZONE_RESETALL, &(q)->queue_flags)
-#define blk_queue_dax(q)	test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
+#define blk_queue_dax(q)	((q)->limits.features & BLK_FEAT_DAX)
 #define blk_queue_pci_p2pdma(q)	\
 	test_bit(QUEUE_FLAG_PCI_P2PDMA, &(q)->queue_flags)
 #ifdef CONFIG_BLK_RQ_ALLOC_TIME