md/md-bitmap: support discard for bitmap ops

Use two new methods {start, end}_discard in bitmap_ops and a new field 'rw'
in struct md_io_clone to handle discard IO, prepare to support new md
bitmap.

Since all bitmap functions to hanlde write IO are the same, also add
typedef to make code cleaner.

Link: https://lore.kernel.org/linux-raid/20250829080426.1441678-4-yukuai1@huaweicloud.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Li Nan <linan122@huawei.com>

drivers/md/md-bitmap.c

@@ -3005,6 +3005,9 @@ static struct bitmap_operations bitmap_ops = {
 
 	.start_write		= bitmap_start_write,
 	.end_write		= bitmap_end_write,
+	.start_discard		= bitmap_start_write,
+	.end_discard		= bitmap_end_write,
+
 	.start_sync		= bitmap_start_sync,
 	.end_sync		= bitmap_end_sync,
 	.cond_end_sync		= bitmap_cond_end_sync,

drivers/md/md-bitmap.h

@@ -61,6 +61,9 @@ struct md_bitmap_stats {
 	struct file	*file;
 };
 
+typedef void (md_bitmap_fn)(struct mddev *mddev, sector_t offset,
+			    unsigned long sectors);
+
 struct bitmap_operations {
 	struct md_submodule_head head;
 
@@ -81,10 +84,11 @@ struct bitmap_operations {
 	void (*end_behind_write)(struct mddev *mddev);
 	void (*wait_behind_writes)(struct mddev *mddev);
 
-	void (*start_write)(struct mddev *mddev, sector_t offset,
-			    unsigned long sectors);
-	void (*end_write)(struct mddev *mddev, sector_t offset,
-			  unsigned long sectors);
+	md_bitmap_fn *start_write;
+	md_bitmap_fn *end_write;
+	md_bitmap_fn *start_discard;
+	md_bitmap_fn *end_discard;
+
 	bool (*start_sync)(struct mddev *mddev, sector_t offset,
 			   sector_t *blocks, bool degraded);
 	void (*end_sync)(struct mddev *mddev, sector_t offset, sector_t *blocks);

drivers/md/md.c

@@ -8933,18 +8933,24 @@ EXPORT_SYMBOL_GPL(md_submit_discard_bio);
 static void md_bitmap_start(struct mddev *mddev,
 			    struct md_io_clone *md_io_clone)
 {
+	md_bitmap_fn *fn = unlikely(md_io_clone->rw == STAT_DISCARD) ?
+			   mddev->bitmap_ops->start_discard :
+			   mddev->bitmap_ops->start_write;
+
 	if (mddev->pers->bitmap_sector)
 		mddev->pers->bitmap_sector(mddev, &md_io_clone->offset,
 					   &md_io_clone->sectors);
 
-	mddev->bitmap_ops->start_write(mddev, md_io_clone->offset,
-				       md_io_clone->sectors);
+	fn(mddev, md_io_clone->offset, md_io_clone->sectors);
 }
 
 static void md_bitmap_end(struct mddev *mddev, struct md_io_clone *md_io_clone)
 {
-	mddev->bitmap_ops->end_write(mddev, md_io_clone->offset,
-				     md_io_clone->sectors);
+	md_bitmap_fn *fn = unlikely(md_io_clone->rw == STAT_DISCARD) ?
+			   mddev->bitmap_ops->end_discard :
+			   mddev->bitmap_ops->end_write;
+
+	fn(mddev, md_io_clone->offset, md_io_clone->sectors);
 }
 
 static void md_end_clone_io(struct bio *bio)
@@ -8983,6 +8989,7 @@ static void md_clone_bio(struct mddev *mddev, struct bio **bio)
 	if (bio_data_dir(*bio) == WRITE && md_bitmap_enabled(mddev, false)) {
 		md_io_clone->offset = (*bio)->bi_iter.bi_sector;
 		md_io_clone->sectors = bio_sectors(*bio);
+		md_io_clone->rw = op_stat_group(bio_op(*bio));
 		md_bitmap_start(mddev, md_io_clone);
 	}
 

drivers/md/md.h

@@ -872,6 +872,7 @@ struct md_io_clone {
 	unsigned long	start_time;
 	sector_t	offset;
 	unsigned long	sectors;
+	enum stat_group	rw;
 	struct bio	bio_clone;
 };