Re: [PATCH 2/3] block: unexport blk_rq_append_bio

[Boaz Harrosh <bharrosh@panasas.com>]

FUJITA Tomonori wrote:
> On Wed, 11 Feb 2009 11:15:53 +0200
> Boaz Harrosh <bharrosh@panasas.com> wrote:
> 
>> I spoke too soon. There is one more place that uses blk_rq_append_bio, that is
>> the place that adds the read/write bio that is received in osd_req_write/read.
>> The reason I receive a bio at these is because mainly I need a way to
>> accept struct page* arrays, as well as kernel & user pointers. A bio is a nice
> 
> The API using an array of pointers to page can handle everything. So
> why do the users of ULD (some rare file systems, I guess), osd
> initiator, need to build bios and pass them?
> 
> 
>> general carrier for any type of memory. Given a bio at hand there are no ways
>> left to prepare a request from it save the FS generic_make_request() route.
>>
>> I was thinking of using struct sg_iovec* at one stage but they look very
>> scary when used with page*, and mapping a page to a pointer but not doing
>> cache sync and all that jazz. A bio is a very nice carrier of a scatter-gather
>> list of memory. It has all the API for any needs. blk_rq_append_bio() was the last
>> way to associate a bio with a request. (except for privileged block-filesystems)
> 
> We need to remove the usage of blk_rq_append_bio() in scsi.
> 
> 
>> So the first thing we have to decide is what API we need at read/write
>> today there is:
> 
> You are talking about the API for osd file systems (or something
> related with osd), right? If so, I think that you can do whatever you
> want to do now. You can make a mistake since it's in-kernel API.
> 
> 
>> void osd_req_read(struct osd_request *or,
>> 	const struct osd_obj_id *, struct bio *data_in, u64 offset);
>>
>> in exofs I use these two:
>>
>> int osd_req_read_kern(struct osd_request *or,
>> 	const struct osd_obj_id *obj, u64 offset, void *buff, u64 len);
>> int osd_req_read_pages(struct osd_request *or,
>> 	const struct osd_obj_id *, u64 offset, u64 length,
>> 	struct page **pages, int page_count);
>>
> 
> As I wrote above, if you have an interface handling 'struct page
> **pages', then there should be ok.

Sorry you miss understand me, I did not explain well.

int osd_req_read_pages(,,,, struct page **pages, int page_count);

Is in exofs.ko. It builds a bio out of **pages then calls
osd_req_read(,,bio,) which will then call blk_rq_append_bio()

So for exofs (filesystem) and pNFS-objects layout driver (Also part of filesystem)
I currently need blk_rq_append_bio(), unless we want to do something new for
these people.

Thanks
Boaz