[PATCH 0/2] Change type-2 dif to use rq embedded 32 byte cdb

[Rob Evers <revers@redhat.com>]

These patches replace the original t10 type 2 dif mempool implementation
by increasing the block and scsi cdb maximum sizes from 16 to 32 bytes.
The cdb embedded in the request structure can then be used for type 2
dif commands, or other 32 byte cdbs as required.

Motivation for this is that type-2 dif commands should be treated as
any other read/writes generally, without any performance penalty.

This patch set conflicts with a patch previously posted which addresses
a race in UA induced retries with type 2 dif commands.  These patches also
address that problem:

http://marc.info/?l=linux-scsi&m=135186352200668&w=2

Testing:

Readily reproduced the race condition panic by simultaneously
inducing UAs while load testing 8 scsi_debug devices.  With patch
applied, same testing ran for 15 hours without a panic.

Sanity tested performance using scsi_debug, with and without
type 2 dif enabled.  Order 80% performance increase noticed
with patches when scsi_debug was running in dif type 2 mode.
Running scsi_debug without type 2 dif, performance was approximately
equal.

Used 3.7.0-rc5 for testing and patch generation.

root (2):
  Change the cdb size limits in block and scsi to 32 bytes
  Change dif type 2 commands to use embedded 32 byte cdb

 drivers/scsi/sd.c        | 45 +--------------------------------------------
 drivers/scsi/sd.h        |  5 -----
 include/linux/blkdev.h   |  2 +-
 include/scsi/scsi_cmnd.h | 13 ++-----------
 4 files changed, 4 insertions(+), 61 deletions(-)

-- 
1.7.11.7