linux/drivers/s390/block
Kent Overstreet 54efd50bfd block: make generic_make_request handle arbitrarily 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_fn() callbacks 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)
 * mtip_submit_request (drivers/block/mtip32xx/mtip32xx.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.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Cc: drbd-user@lists.linbit.com
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Jim Paris <jim@jtan.com>
Cc: Philip Kelleher <pjk1939@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Oleg Drokin <oleg.drokin@intel.com>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Acked-by: NeilBrown <neilb@suse.de> (for the 'md/md.c' bits)
Acked-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
[dpark: skip more mq-based drivers, resolve merge conflicts, etc.]
Signed-off-by: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-08-13 12:31:33 -06:00
..
dasd_3990_erp.c s390/time: rename tod clock access functions 2013-02-14 15:55:10 +01:00
dasd_alias.c s390/dasd: fix kernel panic when alias is set offline 2015-07-13 11:02:14 +02:00
dasd_devmap.c s390/dasd: add support for control unit initiated reconfiguration 2014-10-09 09:13:54 +02:00
dasd_diag.c s390/irq: Use defines for external interruption codes 2014-04-03 14:30:52 +02:00
dasd_diag.h s390: remove 31 bit support 2015-03-25 11:49:33 +01:00
dasd_eckd.c s390/dasd: fix inability to set a DASD device offline 2015-04-15 12:23:50 +02:00
dasd_eckd.h s390/dasd: add support for control unit initiated reconfiguration 2014-10-09 09:13:54 +02:00
dasd_eer.c s390/time: rename tod clock access functions 2013-02-14 15:55:10 +01:00
dasd_erp.c s390/dasd: fix statistics for recovered requests 2013-08-28 09:19:34 +02:00
dasd_fba.c s390: remove 31 bit support 2015-03-25 11:49:33 +01:00
dasd_fba.h
dasd_genhd.c s390/block/dasd: remove obsolete while -EBUSY loop 2015-05-20 09:06:17 -06:00
dasd_int.h s390/dasd: cleanup profiling 2015-01-29 09:19:29 +01:00
dasd_ioctl.c s390/dasd: fix camel case 2014-08-01 11:16:18 +02:00
dasd_proc.c s390/dasd: cleanup profiling 2015-01-29 09:19:29 +01:00
dasd.c s390/dasd: fix kernel panic when alias is set offline 2015-07-13 11:02:14 +02:00
dcssblk.c block: make generic_make_request handle arbitrarily sized bios 2015-08-13 12:31:33 -06:00
Kconfig
Makefile
scm_blk_cluster.c s390/scm_block: fix off by one during cluster reservation 2015-02-26 09:24:47 +01:00
scm_blk.c s390/scm_block: make the number of reqs per HW req configurable 2014-12-08 09:42:47 +01:00
scm_blk.h s390/scm_block: make the number of reqs per HW req configurable 2014-12-08 09:42:47 +01:00
scm_drv.c s390/scm_block: fix printk format string 2013-03-21 13:35:37 +01:00
xpram.c block: make generic_make_request handle arbitrarily sized bios 2015-08-13 12:31:33 -06:00