linux-kernel - Re: [PATCH 1/8] exofs: Kbuild, Headers and osd utils

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Date:	Mon, 16 Feb 2009 10:49:39 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	avishay@...il.com, jeff@...zik.org, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, osd-dev@...n-osd.org,
	linux-kernel@...r.kernel.org,
	James.Bottomley@...senPartnership.com, jens.axboe@...cle.com,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/8] exofs: Kbuild, Headers and osd utils

FUJITA Tomonori wrote:
> On Mon,  9 Feb 2009 15:12:09 +0200
> Boaz Harrosh <bharrosh@...asas.com> wrote:
> 
>> This patch includes osd infrastructure that will be used later by
>> the file system.
>>
>> Also the declarations of constants, on disk structures,
>> and prototypes.
>>
>> And the Kbuild+Kconfig files needed to build the exofs module.
>>
>> Signed-off-by: Boaz Harrosh <bharrosh@...asas.com>
>> ---
>>  fs/exofs/Kbuild   |   30 +++++++
>>  fs/exofs/Kconfig  |   13 +++
>>  fs/exofs/common.h |  181 +++++++++++++++++++++++++++++++++++++++++
>>  fs/exofs/exofs.h  |  139 ++++++++++++++++++++++++++++++++
>>  fs/exofs/osd.c    |  230 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  5 files changed, 593 insertions(+), 0 deletions(-)
>>  create mode 100644 fs/exofs/Kbuild
>>  create mode 100644 fs/exofs/Kconfig
>>  create mode 100644 fs/exofs/common.h
>>  create mode 100644 fs/exofs/exofs.h
>>  create mode 100644 fs/exofs/osd.c
> 
>> +static void _osd_read(struct osd_request *or,
>> +	const struct osd_obj_id *obj, uint64_t offset, struct bio *bio)
>> +{
>> +	osd_req_read(or, obj, bio, offset);
>> +	EXOFS_DBGMSG("osd_req_read(p=%llX, ob=%llX, l=%llu, of=%llu)\n",
>> +		_LLU(obj->partition), _LLU(obj->id), _LLU(bio->bi_size),
>> +		_LLU(offset));
>> +}
>> +
>> +#ifdef __KERNEL__
> 
> Hmm?
> 

Yep, this file also complies in user mode.

>> +static struct bio *_bio_map_pages(struct request_queue *req_q,
>> +				  struct page **pages, unsigned page_count,
>> +				  size_t length, gfp_t gfp_mask)
>> +{
>> +	struct bio *bio;
>> +	int i;
>> +
>> +	bio = bio_alloc(gfp_mask, page_count);
>> +	if (!bio) {
>> +		EXOFS_DBGMSG("Failed to bio_alloc page_count=%d\n", page_count);
>> +		return NULL;
>> +	}
>> +
>> +	for (i = 0; i < page_count && length; i++) {
>> +		size_t use_len = min(length, PAGE_SIZE);
>> +
>> +		if (use_len !=
>> +		    bio_add_pc_page(req_q, bio, pages[i], use_len, 0)) {
>> +			EXOFS_ERR("Failed bio_add_pc_page req_q=%p pages[i]=%p "
>> +				  "use_len=%Zd page_count=%d length=%Zd\n",
>> +				  req_q, pages[i], use_len, page_count, length);
>> +			bio_put(bio);
>> +			return NULL;
>> +		}
>> +
>> +		length -= use_len;
>> +	}
>> +
>> +	WARN_ON(length);
>> +	return bio;
>> +}
> 
> 1) exofs builds bios by hand.
> 2) exofs passes bio to OSD SCSI ULD.
> 
> As a result, exofs and OSD SCSI ULD need to know the internal of bio,
> that is, you reinvent the bio handling infrastructure, as pointed out
> in another thread in scsi-ml.
> 
> _bio_map_pages is called where the VFS passes an array of a pointer to
> a page frame.
> 
> Why can't you simply pass the array to OSD SCSI ULD? Then OSD SCSI ULD
> can use the block layer helper functions to build a request out of
> pages without knowing the internal of bio.
> 
> 

Because actually this code is wrong and temporary and will change soon.
At vfs write_pages I do not get a linear array of page pointers but a
link-list of pages. This will not fit any current model. Also looking
ahead I will have RAID 0, 1, 5, and 6 on objects of different devices. bio
is the perfect collector for memory information in this situation.

exofs is not the first and only file system who is using bios. Proof of
the matter is that block exports a bio submit routine.

As I said on the other thread, I could live without it for now, for a short while,
but I will regret it badly and it will hurt performance in the long run.

<snip>

Boaz
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