blk-mq: move the DMA mapping code to a separate file

While working on the new DMA API I kept getting annoyed how it was placed
right in the middle of the bio splitting code in blk-merge.c.
Split it out into a separate file.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250513071433.836797-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/Makefile

@@ -5,8 +5,8 @@
 
 obj-y		:= bdev.o fops.o bio.o elevator.o blk-core.o blk-sysfs.o \
 			blk-flush.o blk-settings.o blk-ioc.o blk-map.o \
-			blk-merge.o blk-timeout.o \
-			blk-lib.o blk-mq.o blk-mq-tag.o blk-stat.o \
+			blk-merge.o blk-timeout.o blk-lib.o blk-mq.o \
+			blk-mq-tag.o blk-mq-dma.o blk-stat.o \
 			blk-mq-sysfs.o blk-mq-cpumap.o blk-mq-sched.o ioctl.o \
 			genhd.o ioprio.o badblocks.o partitions/ blk-rq-qos.o \
 			disk-events.o blk-ia-ranges.o early-lookup.o

block/blk-merge.c

@@ -7,7 +7,6 @@
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/blk-integrity.h>
-#include <linux/scatterlist.h>
 #include <linux/part_stat.h>
 #include <linux/blk-cgroup.h>
 
@@ -225,27 +224,6 @@ static inline unsigned get_max_io_size(struct bio *bio,
 	return max_sectors & ~(lbs - 1);
 }
 
-/**
- * get_max_segment_size() - maximum number of bytes to add as a single segment
- * @lim: Request queue limits.
- * @paddr: address of the range to add
- * @len: maximum length available to add at @paddr
- *
- * Returns the maximum number of bytes of the range starting at @paddr that can
- * be added to a single segment.
- */
-static inline unsigned get_max_segment_size(const struct queue_limits *lim,
-		phys_addr_t paddr, unsigned int len)
-{
-	/*
-	 * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
-	 * after having calculated the minimum.
-	 */
-	return min_t(unsigned long, len,
-		min(lim->seg_boundary_mask - (lim->seg_boundary_mask & paddr),
-		    (unsigned long)lim->max_segment_size - 1) + 1);
-}
-
 /**
  * bvec_split_segs - verify whether or not a bvec should be split in the middle
  * @lim:      [in] queue limits to split based on
@@ -473,117 +451,6 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
 	return nr_phys_segs;
 }
 
-struct phys_vec {
-	phys_addr_t	paddr;
-	u32		len;
-};
-
-static bool blk_map_iter_next(struct request *req,
-		struct req_iterator *iter, struct phys_vec *vec)
-{
-	unsigned int max_size;
-	struct bio_vec bv;
-
-	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
-		if (!iter->bio)
-			return false;
-		vec->paddr = bvec_phys(&req->special_vec);
-		vec->len = req->special_vec.bv_len;
-		iter->bio = NULL;
-		return true;
-	}
-
-	if (!iter->iter.bi_size)
-		return false;
-
-	bv = mp_bvec_iter_bvec(iter->bio->bi_io_vec, iter->iter);
-	vec->paddr = bvec_phys(&bv);
-	max_size = get_max_segment_size(&req->q->limits, vec->paddr, UINT_MAX);
-	bv.bv_len = min(bv.bv_len, max_size);
-	bio_advance_iter_single(iter->bio, &iter->iter, bv.bv_len);
-
-	/*
-	 * If we are entirely done with this bi_io_vec entry, check if the next
-	 * one could be merged into it.  This typically happens when moving to
-	 * the next bio, but some callers also don't pack bvecs tight.
-	 */
-	while (!iter->iter.bi_size || !iter->iter.bi_bvec_done) {
-		struct bio_vec next;
-
-		if (!iter->iter.bi_size) {
-			if (!iter->bio->bi_next)
-				break;
-			iter->bio = iter->bio->bi_next;
-			iter->iter = iter->bio->bi_iter;
-		}
-
-		next = mp_bvec_iter_bvec(iter->bio->bi_io_vec, iter->iter);
-		if (bv.bv_len + next.bv_len > max_size ||
-		    !biovec_phys_mergeable(req->q, &bv, &next))
-			break;
-
-		bv.bv_len += next.bv_len;
-		bio_advance_iter_single(iter->bio, &iter->iter, next.bv_len);
-	}
-
-	vec->len = bv.bv_len;
-	return true;
-}
-
-static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
-		struct scatterlist *sglist)
-{
-	if (!*sg)
-		return sglist;
-
-	/*
-	 * If the driver previously mapped a shorter list, we could see a
-	 * termination bit prematurely unless it fully inits the sg table
-	 * on each mapping. We KNOW that there must be more entries here
-	 * or the driver would be buggy, so force clear the termination bit
-	 * to avoid doing a full sg_init_table() in drivers for each command.
-	 */
-	sg_unmark_end(*sg);
-	return sg_next(*sg);
-}
-
-/*
- * Map a request to scatterlist, return number of sg entries setup. Caller
- * must make sure sg can hold rq->nr_phys_segments entries.
- */
-int __blk_rq_map_sg(struct request *rq, struct scatterlist *sglist,
-		    struct scatterlist **last_sg)
-{
-	struct req_iterator iter = {
-		.bio	= rq->bio,
-	};
-	struct phys_vec vec;
-	int nsegs = 0;
-
-	/* the internal flush request may not have bio attached */
-	if (iter.bio)
-		iter.iter = iter.bio->bi_iter;
-
-	while (blk_map_iter_next(rq, &iter, &vec)) {
-		*last_sg = blk_next_sg(last_sg, sglist);
-		sg_set_page(*last_sg, phys_to_page(vec.paddr), vec.len,
-				offset_in_page(vec.paddr));
-		nsegs++;
-	}
-
-	if (*last_sg)
-		sg_mark_end(*last_sg);
-
-	/*
-	 * Something must have been wrong if the figured number of
-	 * segment is bigger than number of req's physical segments
-	 */
-	WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
-
-	return nsegs;
-}
-EXPORT_SYMBOL(__blk_rq_map_sg);
-
 static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
 						  sector_t offset)
 {

block/blk-mq-dma.c

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include "blk.h"
+
+struct phys_vec {
+	phys_addr_t	paddr;
+	u32		len;
+};
+
+static bool blk_map_iter_next(struct request *req, struct req_iterator *iter,
+			      struct phys_vec *vec)
+{
+	unsigned int max_size;
+	struct bio_vec bv;
+
+	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
+		if (!iter->bio)
+			return false;
+		vec->paddr = bvec_phys(&req->special_vec);
+		vec->len = req->special_vec.bv_len;
+		iter->bio = NULL;
+		return true;
+	}
+
+	if (!iter->iter.bi_size)
+		return false;
+
+	bv = mp_bvec_iter_bvec(iter->bio->bi_io_vec, iter->iter);
+	vec->paddr = bvec_phys(&bv);
+	max_size = get_max_segment_size(&req->q->limits, vec->paddr, UINT_MAX);
+	bv.bv_len = min(bv.bv_len, max_size);
+	bio_advance_iter_single(iter->bio, &iter->iter, bv.bv_len);
+
+	/*
+	 * If we are entirely done with this bi_io_vec entry, check if the next
+	 * one could be merged into it.  This typically happens when moving to
+	 * the next bio, but some callers also don't pack bvecs tight.
+	 */
+	while (!iter->iter.bi_size || !iter->iter.bi_bvec_done) {
+		struct bio_vec next;
+
+		if (!iter->iter.bi_size) {
+			if (!iter->bio->bi_next)
+				break;
+			iter->bio = iter->bio->bi_next;
+			iter->iter = iter->bio->bi_iter;
+		}
+
+		next = mp_bvec_iter_bvec(iter->bio->bi_io_vec, iter->iter);
+		if (bv.bv_len + next.bv_len > max_size ||
+		    !biovec_phys_mergeable(req->q, &bv, &next))
+			break;
+
+		bv.bv_len += next.bv_len;
+		bio_advance_iter_single(iter->bio, &iter->iter, next.bv_len);
+	}
+
+	vec->len = bv.bv_len;
+	return true;
+}
+
+static inline struct scatterlist *
+blk_next_sg(struct scatterlist **sg, struct scatterlist *sglist)
+{
+	if (!*sg)
+		return sglist;
+
+	/*
+	 * If the driver previously mapped a shorter list, we could see a
+	 * termination bit prematurely unless it fully inits the sg table
+	 * on each mapping. We KNOW that there must be more entries here
+	 * or the driver would be buggy, so force clear the termination bit
+	 * to avoid doing a full sg_init_table() in drivers for each command.
+	 */
+	sg_unmark_end(*sg);
+	return sg_next(*sg);
+}
+
+/*
+ * Map a request to scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold rq->nr_phys_segments entries.
+ */
+int __blk_rq_map_sg(struct request *rq, struct scatterlist *sglist,
+		    struct scatterlist **last_sg)
+{
+	struct req_iterator iter = {
+		.bio	= rq->bio,
+	};
+	struct phys_vec vec;
+	int nsegs = 0;
+
+	/* the internal flush request may not have bio attached */
+	if (iter.bio)
+		iter.iter = iter.bio->bi_iter;
+
+	while (blk_map_iter_next(rq, &iter, &vec)) {
+		*last_sg = blk_next_sg(last_sg, sglist);
+		sg_set_page(*last_sg, phys_to_page(vec.paddr), vec.len,
+				offset_in_page(vec.paddr));
+		nsegs++;
+	}
+
+	if (*last_sg)
+		sg_mark_end(*last_sg);
+
+	/*
+	 * Something must have been wrong if the figured number of
+	 * segment is bigger than number of req's physical segments
+	 */
+	WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
+
+	return nsegs;
+}
+EXPORT_SYMBOL(__blk_rq_map_sg);

block/blk.h

@@ -404,6 +404,27 @@ static inline struct bio *__bio_split_to_limits(struct bio *bio,
 	}
 }
 
+/**
+ * get_max_segment_size() - maximum number of bytes to add as a single segment
+ * @lim: Request queue limits.
+ * @paddr: address of the range to add
+ * @len: maximum length available to add at @paddr
+ *
+ * Returns the maximum number of bytes of the range starting at @paddr that can
+ * be added to a single segment.
+ */
+static inline unsigned get_max_segment_size(const struct queue_limits *lim,
+		phys_addr_t paddr, unsigned int len)
+{
+	/*
+	 * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
+	 * after having calculated the minimum.
+	 */
+	return min_t(unsigned long, len,
+		min(lim->seg_boundary_mask - (lim->seg_boundary_mask & paddr),
+		    (unsigned long)lim->max_segment_size - 1) + 1);
+}
+
 int ll_back_merge_fn(struct request *req, struct bio *bio,
 		unsigned int nr_segs);
 bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,