On 9/14/2011 12:19 AM, Christoph Hellwig wrote:
On Mon, Sep 12, 2011 at 08:04:46PM +0200, Jens Axboe wrote:
I really hate naming things different from the method they are
implementing. I've tried to figure out what the point of the
old blk_make_request is - why would we not go through
generic_make_request for this?
Boaz, any idea?
I tend to agree, we could rename the existing blk_make_request(). It
could be blk_make_request_from_bio() or something like that, since
that's what it does.
It should at very least be renamed. But I still can't figure out what
it is for exactly.
There are three users:
(1) virtio_blk::virtblk_get_id():
This looks like it really should just use blk_rq_map_kern.
(2) osd_initiator::_make_request():
This one looks like it should just use the same scheme as
sg_io(), as it's doing the same thing.
Good god what sg_io? That broken pointr+length from user-mode that sg.c
and bsg.c are using? no can do it's not user-mode pointers, and it's not
pointer+length it's pages pointers of a bio. The only other structure
that could carry the same information is struct sg, but we work very
hard to get rid of this contraption. (scsi_execute_async or something
that it was)
blk_make_request() was made to be the parallel of __make_request, to be
used from filesystem level users. But with two differences.
1. Mainly support for none-FS BLOCK_PC requests
2. Also support chained bios. (was added later)
(3) target_core_pscsi::__pscsi_map_SG():
Same as (2).
There is no better suitable structure in current Kernel to carry a list
of pages, with optional offset and length, then bio struct. Given a bio
at hand. how do you make a block request out of it? (If it's not an
FS_PC type IO?)
As I remember target_core had their own pages-linked-list structure, and
how do you make a request out of that? again best at hand is bio.
bio is for a long time a page-pointers-carrier-structure and is out of
private block-level use. The filesystem level is full of it.
Thanks
Boaz
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