Introduce the bulk IV mode for improving the crypto engine efficiency

From the dm-crypt performance report, we found it shows low efficiency with crypto engine for some mode (like ecb or xts mode). Because in dm crypt, it will map the IO data buffer with scatterlist, and send the scatterlist of one bio to the encryption engine, if send more scatterlists with bigger size at one time, that helps the engine palys best performance, which means a high encryption speed.

But now the dm-crypt only map one segment (always one sector) of one bio with one scatterlist to the crypto engine at one time. which is more time-consuming and ineffective for the crypto engine. Especially for some modes which don't need different IV for each sector, we can map the whole bio with multiple scatterlists to improve the engine performance.

But this optimization is not support some ciphers and IV modes which should do sector by sector and need different IV for each sector.

Change since v2:
- Introduce blk_bio_map_sg() function to map one bio.
- Do some modifications for checking sg entry.

Baolin Wang (2):
block: Introduce blk_bio_map_sg() to map one bio
md: dm-crypt: Introduce the bulk IV mode for bulk crypto

 block/blk-merge.c      |   45 +++++++
 drivers/md/dm-crypt.c  |  333 +++++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/blkdev.h |    3 +
 3 files changed, 375 insertions(+), 6 deletions(-)

1.7.9.5