iomap: add a bioset pointer to iomap_read_folio_ops

Optionally allocate the bio from the bioset provided in
iomap_read_folio_ops.  If no bioset is provided, fs_bio_set is still
used, which is the standard bioset for file systems.

Based on a patch from Goldwyn Rodrigues <rgoldwyn@suse.com>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260223132021.292832-14-hch@lst.de
Tested-by: Anuj Gupta <anuj20.g@samsung.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

fs/iomap/bio.c

@@ -24,11 +24,19 @@ static void iomap_bio_submit_read(const struct iomap_iter *iter,
 	submit_bio(ctx->read_ctx);
 }
 
+static struct bio_set *iomap_read_bio_set(struct iomap_read_folio_ctx *ctx)
+{
+	if (ctx->ops && ctx->ops->bio_set)
+		return ctx->ops->bio_set;
+	return &fs_bio_set;
+}
+
 static void iomap_read_alloc_bio(const struct iomap_iter *iter,
 		struct iomap_read_folio_ctx *ctx, size_t plen)
 {
 	const struct iomap *iomap = &iter->iomap;
 	unsigned int nr_vecs = DIV_ROUND_UP(iomap_length(iter), PAGE_SIZE);
+	struct bio_set *bio_set = iomap_read_bio_set(ctx);
 	struct folio *folio = ctx->cur_folio;
 	gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
 	gfp_t orig_gfp = gfp;
@@ -47,9 +55,11 @@ static void iomap_read_alloc_bio(const struct iomap_iter *iter,
 	 * having to deal with partial page reads.  This emulates what
 	 * do_mpage_read_folio does.
 	 */
-	bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ, gfp);
+	bio = bio_alloc_bioset(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ,
+			gfp, bio_set);
 	if (!bio)
-		bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
+		bio = bio_alloc_bioset(iomap->bdev, 1, REQ_OP_READ, orig_gfp,
+				bio_set);
 	if (ctx->rac)
 		bio->bi_opf |= REQ_RAHEAD;
 	bio->bi_iter.bi_sector = iomap_sector(iomap, iter->pos);

include/linux/iomap.h

@@ -515,6 +515,12 @@ struct iomap_read_ops {
 	 */
 	void (*submit_read)(const struct iomap_iter *iter,
 			struct iomap_read_folio_ctx *ctx);
+
+	/*
+	 * Optional, allows filesystem to specify own bio_set, so new bio's
+	 * can be allocated from the provided bio_set.
+	 */
+	struct bio_set *bio_set;
 };
 
 /*