return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
}
+/*
+ * Return the maximum number of sectors from the start of a bio that may be
+ * submitted as a single request to a block device. If enough sectors remain,
+ * align the end to the physical block size. Otherwise align the end to the
+ * logical block size. This approach minimizes the number of non-aligned
+ * requests that are submitted to a block device if the start of a bio is not
+ * aligned to a physical block boundary.
+ */
static inline unsigned get_max_io_size(struct request_queue *q,
struct bio *bio)
{
unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
- unsigned mask = queue_logical_block_size(q) - 1;
+ unsigned max_sectors = sectors;
+ unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
+ unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
+ unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
- /* aligned to logical block size */
- sectors &= ~(mask >> 9);
+ max_sectors += start_offset;
+ max_sectors &= ~(pbs - 1);
+ if (max_sectors > start_offset)
+ return max_sectors - start_offset;
- return sectors;
+ return sectors & (lbs - 1);
}
-static unsigned get_max_segment_size(struct request_queue *q,
+static unsigned get_max_segment_size(const struct request_queue *q,
unsigned offset)
{
unsigned long mask = queue_segment_boundary(q);
queue_max_segment_size(q));
}
-/*
- * Split the bvec @bv into segments, and update all kinds of
- * variables.
+/**
+ * bvec_split_segs - verify whether or not a bvec should be split in the middle
+ * @q: [in] request queue associated with the bio associated with @bv
+ * @bv: [in] bvec to examine
+ * @nsegs: [in,out] Number of segments in the bio being built. Incremented
+ * by the number of segments from @bv that may be appended to that
+ * bio without exceeding @max_segs
+ * @sectors: [in,out] Number of sectors in the bio being built. Incremented
+ * by the number of sectors from @bv that may be appended to that
+ * bio without exceeding @max_sectors
+ * @max_segs: [in] upper bound for *@nsegs
+ * @max_sectors: [in] upper bound for *@sectors
+ *
+ * When splitting a bio, it can happen that a bvec is encountered that is too
+ * big to fit in a single segment and hence that it has to be split in the
+ * middle. This function verifies whether or not that should happen. The value
+ * %true is returned if and only if appending the entire @bv to a bio with
+ * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
+ * the block driver.
*/
-static bool bvec_split_segs(struct request_queue *q, struct bio_vec *bv,
- unsigned *nsegs, unsigned *sectors, unsigned max_segs)
+static bool bvec_split_segs(const struct request_queue *q,
+ const struct bio_vec *bv, unsigned *nsegs,
+ unsigned *sectors, unsigned max_segs,
+ unsigned max_sectors)
{
- unsigned len = bv->bv_len;
+ unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
+ unsigned len = min(bv->bv_len, max_len);
unsigned total_len = 0;
- unsigned new_nsegs = 0, seg_size = 0;
+ unsigned seg_size = 0;
- /*
- * Multi-page bvec may be too big to hold in one segment, so the
- * current bvec has to be splitted as multiple segments.
- */
- while (len && new_nsegs + *nsegs < max_segs) {
+ while (len && *nsegs < max_segs) {
seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
seg_size = min(seg_size, len);
- new_nsegs++;
+ (*nsegs)++;
total_len += seg_size;
len -= seg_size;
break;
}
- if (new_nsegs) {
- *nsegs += new_nsegs;
- if (sectors)
- *sectors += total_len >> 9;
- }
+ *sectors += total_len >> 9;
- /* split in the middle of the bvec if len != 0 */
- return !!len;
+ /* tell the caller to split the bvec if it is too big to fit */
+ return len > 0 || bv->bv_len > max_len;
}
+/**
+ * blk_bio_segment_split - split a bio in two bios
+ * @q: [in] request queue pointer
+ * @bio: [in] bio to be split
+ * @bs: [in] bio set to allocate the clone from
+ * @segs: [out] number of segments in the bio with the first half of the sectors
+ *
+ * Clone @bio, update the bi_iter of the clone to represent the first sectors
+ * of @bio and update @bio->bi_iter to represent the remaining sectors. The
+ * following is guaranteed for the cloned bio:
+ * - That it has at most get_max_io_size(@q, @bio) sectors.
+ * - That it has at most queue_max_segments(@q) segments.
+ *
+ * Except for discard requests the cloned bio will point at the bi_io_vec of
+ * the original bio. It is the responsibility of the caller to ensure that the
+ * original bio is not freed before the cloned bio. The caller is also
+ * responsible for ensuring that @bs is only destroyed after processing of the
+ * split bio has finished.
+ */
static struct bio *blk_bio_segment_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs,
if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
goto split;
- if (sectors + (bv.bv_len >> 9) > max_sectors) {
- /*
- * Consider this a new segment if we're splitting in
- * the middle of this vector.
- */
- if (nsegs < max_segs &&
- sectors < max_sectors) {
- /* split in the middle of bvec */
- bv.bv_len = (max_sectors - sectors) << 9;
- bvec_split_segs(q, &bv, &nsegs,
- §ors, max_segs);
- }
+ if (nsegs < max_segs &&
+ sectors + (bv.bv_len >> 9) <= max_sectors &&
+ bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
+ nsegs++;
+ sectors += bv.bv_len >> 9;
+ } else if (bvec_split_segs(q, &bv, &nsegs, §ors, max_segs,
+ max_sectors)) {
goto split;
}
- if (nsegs == max_segs)
- goto split;
-
bvprv = bv;
bvprvp = &bvprv;
-
- if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
- nsegs++;
- sectors += bv.bv_len >> 9;
- } else if (bvec_split_segs(q, &bv, &nsegs, §ors,
- max_segs)) {
- goto split;
- }
}
*segs = nsegs;
return bio_split(bio, sectors, GFP_NOIO, bs);
}
+/**
+ * __blk_queue_split - split a bio and submit the second half
+ * @q: [in] request queue pointer
+ * @bio: [in, out] bio to be split
+ * @nr_segs: [out] number of segments in the first bio
+ *
+ * Split a bio into two bios, chain the two bios, submit the second half and
+ * store a pointer to the first half in *@bio. If the second bio is still too
+ * big it will be split by a recursive call to this function. Since this
+ * function may allocate a new bio from @q->bio_split, it is the responsibility
+ * of the caller to ensure that @q is only released after processing of the
+ * split bio has finished.
+ */
void __blk_queue_split(struct request_queue *q, struct bio **bio,
unsigned int *nr_segs)
{
}
}
+/**
+ * blk_queue_split - split a bio and submit the second half
+ * @q: [in] request queue pointer
+ * @bio: [in, out] bio to be split
+ *
+ * Split a bio into two bios, chains the two bios, submit the second half and
+ * store a pointer to the first half in *@bio. Since this function may allocate
+ * a new bio from @q->bio_split, it is the responsibility of the caller to
+ * ensure that @q is only released after processing of the split bio has
+ * finished.
+ */
void blk_queue_split(struct request_queue *q, struct bio **bio)
{
unsigned int nr_segs;
unsigned int blk_recalc_rq_segments(struct request *rq)
{
unsigned int nr_phys_segs = 0;
+ unsigned int nr_sectors = 0;
struct req_iterator iter;
struct bio_vec bv;
}
rq_for_each_bvec(bv, rq, iter)
- bvec_split_segs(rq->q, &bv, &nr_phys_segs, NULL, UINT_MAX);
+ bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
+ UINT_MAX, UINT_MAX);
return nr_phys_segs;
}
projects / linux-2.6-block.git / blobdiff