path: root/include/linux/blkdev.h
diff options
authorKent Overstreet <>2014-06-16 21:16:20 -0700
committerKent Overstreet <>2014-06-16 21:16:36 -0700
commitcd0e67eb0455ef9ef46e8a185cfd9c2f6c0a5c48 (patch)
treea67207e469370112fb01ac471555c65c4c915b87 /include/linux/blkdev.h
parent16b9057804c02e2d351e9c8f606e909b43cbd9e7 (diff)
block: Make generic_make_request handle arbitrary sized bios
The way the block layer is currently written, it goes to great lengths to avoid having to split bios; upper layer code (such as bio_add_page()) checks what the underlying device can handle and tries to always create bios that don't need to be split. But this approach becomes unwieldy and eventually breaks down with stacked devices and devices with dynamic limits, and it adds a lot of complexity. If the block layer could split bios as needed, we could eliminate a lot of complexity elsewhere - particularly in stacked drivers. Code that creates bios can then create whatever size bios are convenient, and more importantly stacked drivers don't have to deal with both their own bio size limitations and the limitations of the (potentially multiple) devices underneath them. In the future this will let us delete merge_bvec_fn and a bunch of other code. We do this by adding calls to blk_queue_split() to the various make_request functions that need it - a few can already handle arbitrary size bios. Note that we add the call _after_ any call to blk_queue_bounce(); this means that blk_queue_split() and blk_recalc_rq_segments() don't need to be concerned with bouncing affecting segment merging. Some make_request_fns were simple enough to audit and verify they don't need blk_queue_split() calls. The skipped ones are: * nfhd_make_request (arch/m68k/emu/nfblock.c) * axon_ram_make_request (arch/powerpc/sysdev/axonram.c) * simdisk_make_request (arch/xtensa/platforms/iss/simdisk.c) * brd_make_request (ramdisk - drivers/block/brd.c) * loop_make_request * null_queue_bio * bcache's make_request fns Some others are almost certainly safe to remove now, but will be left for future patches. Signed-off-by: Kent Overstreet <> Cc: Jens Axboe <> Cc: Neil Brown <> Cc: Alasdair Kergon <> Cc: Cc: Lars Ellenberg <> Cc: Cc: Asai Thambi S P <> Cc: Sam Bradshaw <> Cc: Matthew Wilcox <> Cc: Cc: Jiri Kosina <> Cc: Geoff Levand <> Cc: Jim Paris <> Cc: Joshua Morris <> Cc: Philip Kelleher <> Cc: Minchan Kim <> Cc: Nitin Gupta <> Cc: Martin Schwidefsky <> Cc: Heiko Carstens <> Cc: Peng Tao <>
Diffstat (limited to 'include/linux/blkdev.h')
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 31e11051f1ba..78718c9e2ac7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -488,6 +488,7 @@ struct request_queue {
struct blk_mq_tag_set *tag_set;
struct list_head tag_set_list;
+ struct bio_set *bio_split;
#define QUEUE_FLAG_QUEUED 1 /* uses generic tag queueing */
@@ -810,6 +811,8 @@ extern void blk_rq_unprep_clone(struct request *rq);
extern int blk_insert_cloned_request(struct request_queue *q,
struct request *rq);
extern void blk_delay_queue(struct request_queue *, unsigned long);
+extern void blk_queue_split(struct request_queue *, struct bio **,
+ struct bio_set *);
extern void blk_recount_segments(struct request_queue *, struct bio *);
extern int scsi_verify_blk_ioctl(struct block_device *, unsigned int);
extern int scsi_cmd_blk_ioctl(struct block_device *, fmode_t,