Hi all
In an effort to remove blk_rq_append_bio() and only use well published
block API, I would like to propose the below solution for OSD and exofs.
Current discussion has two sides:
* blk_make_request():
exofs and other non-block-based filesystems can use a bio, in which
case a well established block API should allow of allocating a request
given a bio.
* blk_rq_map_pages():
Let filesystems submit an array of page-pointers, and refrain from using
bio(s). bio(s) is a privilege of block-based filesystems only.
The first solution is trivial, robust, safe with minimum changes and impact.
It will allow any future directions easily.
I have also implemented a second approach with the use of a new
blk_rq_map_pages. It works, all exofs tests pass successfully just
as with today's code. But I hate it because:
* Jeff Garzik is working on a block-over-osd-object block-device.
I'm not sure of his plans, but sitting under block-layer at it's
prepare_fn routine, the most trivial solution is to pass the bio
as is to libosd. Otherwise he will need to copy and recopy all these
pages information.
Jeff please comment.
* Use of the in-kernel raid engines.
Current dm-raid engines are heavily bio based. If we want to tap into-that
(And we must) from exofs and pNFS-objects-layout we have no choice but to
use bio(s) and be able to submit bios.
* For any none trivial usage, even today. bio is more stable, robust
faster. and less code since it is already there.
Here is some code:
[PATCHSET 0/2] Allow append of kernel pointers to request
[PATCH 1/4] allow blk_rq_map_kern to append to requests
[PATCH 2/4] libosd: Use new blk_rq_map_kern
These two patches are not disputable and safe and should go in as is
even to 2.6.30. They remove one usage of blk_rq_append_bio from the
osd_initiator.
[PROPOSAL_1 0/2] blk_make_request()
[PATCH 3/4] [RFC] Export new blk_make_request() which takes bio and returns request
[PATCH 4/4] libosd: Use of new blk_make_request
This is option one above. Trivial, cosmetic, no core changes.
[PROPOSAL_2 0/5] blk_rq_map_pages()
[RFC 1/5] blk_rq_map_pages() new API
[RFC 2/5] libosd: Rename osd_req_write/read to osd_req_write/read_old
[RFC 3/5] libosd: No bio for you
[RFC 4/5] exofs: No bio for you
[RFC 5/5] libosd: Remove deprecated bio based API
This is option two above. Needs lots of core changes to exofs.
After patch 5/5 code runs well, all tests pass. There is
runtime bisectability problem, the exofs will not run between
[3/5]-[4/5].
Please advise
Boaz
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