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Date: Wed, 15 Jul 2009 11:19:35 +0300
From: Boaz Harrosh <bharrosh@...asas.com>
To: Vladislav Bolkhovitin <vst@...b.net>
CC: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
scst-devel@...ts.sourceforge.net, Tejun Heo <tj@...nel.org>,
James Bottomley <James.Bottomley@...senPartnership.com>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH]: New implementation of scsi_execute_async()
On 07/14/2009 07:16 PM, Vladislav Bolkhovitin wrote:
> Boaz Harrosh wrote:
>> On 07/09/2009 09:14 PM, Vladislav Bolkhovitin wrote:
>>> This patch reimplements scsi_execute_async(). In the new version it's a lot less
>>> hackish and also has additional features. Namely:
>>>
>>> 1. Possibility to insert commands both in tail and in head of the queue.
>>>
>>> 2. Possibility to explicitly specify if the last SG element has space for padding.
>>>
>>> This patch based on the previous patches posted by Tejun Heo. Comparing to them
>>> it has the following improvements:
>>>
>>> 1. It uses BIOs chaining instead of kmalloc()ing the whole bio.
>>>
>>> 2. It uses SGs chaining instead of kmalloc()ing one big SG in case if direct
>>> mapping failed (e.g. because of DMA alignment or padding).
>>>
>>> 3. If direct mapping failed, if possible, it copies only the last SG element,
>>> not the whole SG.
>>>
>>> Also this patch adds and exports function blk_copy_sg(), which copies one SG to
>>> another.
>>>
>>> At the moment SCST is the only user of this functionality. It needs it, because
>>> its target drivers, which are, basically, SCSI drivers, can deal only with SGs,
>>> not with BIOs. But, according the latest discussions, there are other potential
>>> users for of this functionality, so I'm sending this patch in a hope that it will be
>>> also useful for them and eventually will be merged in the mainline kernel.
>>>
>>> This patch requires previously sent patch with subject "[PATCH]: Rename REQ_COPY_USER
>>> to more descriptive REQ_HAS_TAIL_SPACE_FOR_PADDING".
>>>
>>> It's against 2.6.30.1, but if necessary, I can update it to any necessary
>>> kernel version.
>>>
>>> Signed-off-by: Vladislav Bolkhovitin <vst@...b.net>
>>>
>>> block/blk-map.c | 536 +++++++++++++++++++++++++++++++++++++++++++++
>>> drivers/scsi/scsi_lib.c | 108 ++++++++-
>>> include/linux/blkdev.h | 6
>>> include/scsi/scsi_device.h | 11
>>> 4 files changed, 660 insertions(+), 1 deletion(-)
>>>
>> The scsi bits are not needed and just add complexity.
>> allocate the request, call blk_rq_map_kern_sg() and
>> blk_execute_xxx directly from your driver. Since you exacly
>> know your code path lots of if(s) and flags are saved and that ugly
>> scsi_io_context allocation.
>
> Are you against any helper functions? scsi_lib.c has only scsi_execute_async(),
> which is a small helper function, which only hides internal machinery details.
> All the flags it has are needed and can't be avoided, especially
> SCSI_ASYNC_EXEC_FLAG_HAS_TAIL_SPACE_FOR_PADDING
>
Yes I'm sure. This will not be accepted. Just do it directly in the driver
like all other ULD's and block layer users. Use direct blk API. All these little
things and flags you are talking about are block specific, there is no single thing
SCSI about them.
> The allocation of scsi_io_context is unavoidable, because sense buffer should
> be allocated anyway.
>
NO!, driver needs to do it's job and provide a sense buffer and call blk API
just like all the other drivers. this has nothing to do with SCSI.
>> If you absolutely need that scsi_normalize_sense() of scsi_execute_req
>> call it from driver, its already exported.
>
> No, I don't need scsi_normalize_sense() and not use it anywhere.
>
Sorry yes I was spaced out for a sec.
>>> diff -upkr linux-2.6.30.1/block/blk-map.c linux-2.6.30.1/block/blk-map.c
>>> --- linux-2.6.30.1/block/blk-map.c 2009-06-10 07:05:27.000000000 +0400
>>> +++ linux-2.6.30.1/block/blk-map.c 2009-07-09 21:33:07.000000000 +0400
>>> @@ -5,6 +5,7 @@
>>> #include <linux/module.h>
>>> #include <linux/bio.h>
>>> #include <linux/blkdev.h>
>>> +#include <linux/scatterlist.h>
>>> #include <scsi/sg.h> /* for struct sg_iovec */
>>>
>>> #include "blk.h"
>>> @@ -273,6 +274,541 @@ int blk_rq_unmap_user(struct bio *bio)
>>> EXPORT_SYMBOL(blk_rq_unmap_user);
>>>
>>> /**
>>> + * blk_copy_sg - copy one SG vector to another
>>> + * @dst_sg: destination SG
>>> + * @src_sg: source SG
>>> + * @copy_len: maximum amount of data to copy. If 0, then copy all.
>>> + * @d_km_type: kmap_atomic type for the destination SG
>>> + * @s_km_type: kmap_atomic type for the source SG
>>> + *
>>> + * Description:
>>> + * Data from the destination SG vector will be copied to the source SG
>>> + * vector. End of the vectors will be determined by sg_next() returning
>>> + * NULL. Returns number of bytes copied.
>>> + */
>>> +int blk_copy_sg(struct scatterlist *dst_sg,
>>> + struct scatterlist *src_sg, size_t copy_len,
>>> + enum km_type d_km_type, enum km_type s_km_type)
>>> +{
>>> + int res = 0;
>>> + size_t src_len, dst_len, src_offs, dst_offs;
>>> + struct page *src_page, *dst_page;
>>> +
>>> + if (copy_len == 0)
>>> + copy_len = 0x7FFFFFFF; /* copy all */
>>> +
>>> + dst_page = sg_page(dst_sg);
>>> + dst_len = dst_sg->length;
>>> + dst_offs = dst_sg->offset;
>>> +
>>> + src_offs = 0;
>>> + do {
>>> + src_page = sg_page(src_sg);
>>> + src_len = src_sg->length;
>>> + src_offs = src_sg->offset;
>>> +
>>> + do {
>>> + void *saddr, *daddr;
>>> + size_t n;
>>> +
>>> + saddr = kmap_atomic(src_page, s_km_type) + src_offs;
>>> + daddr = kmap_atomic(dst_page, d_km_type) + dst_offs;
>>> +
>>> + if ((src_offs == 0) && (dst_offs == 0) &&
>>> + (src_len >= PAGE_SIZE) && (dst_len >= PAGE_SIZE) &&
>>> + (copy_len >= PAGE_SIZE)) {
>>> + copy_page(daddr, saddr);
>>> + n = PAGE_SIZE;
>>> + } else {
>>> + n = min_t(size_t, PAGE_SIZE - dst_offs,
>>> + PAGE_SIZE - src_offs);
>>> + n = min(n, src_len);
>>> + n = min(n, dst_len);
>>> + n = min_t(size_t, n, copy_len);
>>> + memcpy(daddr, saddr, n);
>>> + dst_offs += n;
>>> + src_offs += n;
>>> + }
>>> +
>>> + kunmap_atomic(saddr, s_km_type);
>>> + kunmap_atomic(daddr, d_km_type);
>>> +
>>> + res += n;
>>> + copy_len -= n;
>>> + if (copy_len == 0)
>>> + goto out;
>>> +
>>> + if ((src_offs & ~PAGE_MASK) == 0) {
>>> + src_page = nth_page(src_page, 1);
>>> + src_offs = 0;
>>> + }
>>> + if ((dst_offs & ~PAGE_MASK) == 0) {
>>> + dst_page = nth_page(dst_page, 1);
>>> + dst_offs = 0;
>>> + }
>>> +
>>> + src_len -= n;
>>> + dst_len -= n;
>>> + if (dst_len == 0) {
>>> + dst_sg = sg_next(dst_sg);
>>> + if (dst_sg == NULL)
>>> + goto out;
>>> + dst_page = sg_page(dst_sg);
>>> + dst_len = dst_sg->length;
>>> + dst_offs = dst_sg->offset;
>>> + }
>>> + } while (src_len > 0);
>>> +
>>> + src_sg = sg_next(src_sg);
>>> + } while (src_sg != NULL);
>>> +
>>> +out:
>>> + return res;
>>> +}
>>> +EXPORT_SYMBOL(blk_copy_sg);
>>> +
>> This has nothing to do with block layer lib/scatterlist.c is a better
>> candidate.
>
> Done. V2 of the patch is coming.
>
>> see if you can refactor it better together with sg_copy_to/from_buffer
>
> Unfortunately, they can't be used, because in there is a need to copy one SG
> entry to another (sg_copy_elem() in the V2). Using sg_copy_elem() sg_copy()
> implemented in just a few tens LOC.
>
>>> +/**
>>> + * blk_rq_unmap_kern_sg - "unmaps" data buffers in the request
>>> + * @req: request to unmap
>>> + * @do_copy: sets copy data between buffers, if needed, or not
>>> + *
>>> + * Description:
>>> + * It frees all additional buffers allocated for SG->BIO mapping.
>>> + */
>>> +void blk_rq_unmap_kern_sg(struct request *req, int do_copy)
>>> +{
>>> + struct scatterlist *hdr = (struct scatterlist *)req->end_io_data;
>>> +
>> You can't use req->end_io_data here! req->end_io_data is reserved for
>> blk_execute_async callers. It can not be used for private block use.
>
> Why? I see blk_execute_rq() happily uses it. Plus, I implemented stacking of
> it in scsi_execute_async().
>
As I said users of blk_execute_rq_nowait() blk_execute_rq is a user of
blk_execute_rq_nowait just as the other guy.
"implemented stacking" is exactly the disaster I'm talking about.
Also it totaly breaks the blk API. Now I need to to specific code
when mapping with this API as opposed to other mappings when I execute
> Do you have better suggestion?
>
I have not look at it deeply but you'll need another system. Perhaps
like map_user/unmap_user where you give unmap_user the original bio.
Each user of map_user needs to keep a pointer to the original bio
on mapping. Maybe some other options as well. You can use the bio's
private data pointer, when building the first bio from scatter-list.
>> (Don't you use it in this patchset from scsi_execute_async ?)
>
> As I wrote, I used patches posted by Tejun Heo.
>
>>> + if (hdr == NULL)
>>> + goto out;
>>> +
>>> + if (hdr->length == 0) {
>>> + /* Tail element only was copied */
>>> + struct scatterlist *new_sg = &hdr[1];
>>> + struct scatterlist *orig_sg = (struct scatterlist *)hdr->page_link;
>>> +
>> I don't like that overloading of (scatterlist *) like that. Put a well defined struct
>> or union with proper flags and types, so all possibilities are clear at both sides of
>> the code. Document that structure for the different options.
>
> Done.
>
>>> + if ((rq_data_dir(req) == READ) && do_copy) {
>>> + void *saddr, *daddr;
>>> +
>>> + saddr = kmap_atomic(sg_page(orig_sg), KM_BIO_SRC_IRQ);
>>> + daddr = kmap_atomic(sg_page(new_sg), KM_BIO_DST_IRQ) +
>>> + new_sg->offset;
>>> + memcpy(daddr, saddr, orig_sg->length);
>>> + kunmap_atomic(saddr, KM_BIO_SRC_IRQ);
>>> + kunmap_atomic(daddr, KM_BIO_DST_IRQ);
>>> + }
>>> +
>>> + __free_pages(sg_page(orig_sg), get_order(orig_sg->length));
>>> + *orig_sg = *new_sg;
>>> + kfree(hdr);
>>> + } else {
>>> + /* The whole SG was copied */
>>> + struct scatterlist *new_sgl = &hdr[1];
>>> + struct scatterlist *orig_sgl = (struct scatterlist *)hdr->page_link;
>>> + struct scatterlist *sg, *start_sg;
>> Here too ugly as hell, use a proper structure with the needed types.
>
> The same.
>
>>> + int n;
>>> +
>>> + if ((rq_data_dir(req) == READ) && do_copy) {
>>> + blk_copy_sg(orig_sgl, new_sgl, 0, KM_BIO_DST_IRQ,
>>> + KM_BIO_SRC_IRQ);
>>> + }
>>> +
>>> + start_sg = hdr;
>>> + sg = new_sgl;
>>> + n = 1;
>>> + while (sg != NULL) {
>>> + __free_page(sg_page(sg));
>>> + sg = sg_next(sg);
>>> + n++;
>>> + /* One entry for chaining */
>>> + if ((sg == NULL) || (n == (SG_MAX_SINGLE_ALLOC - 1))) {
>>> + kfree(start_sg);
>>> + start_sg = sg;
>>> + n = 0;
>>> + }
>>> + }
>>> + }
>>> +
>>> +out:
>>> + return;
>>> +}
>>> +EXPORT_SYMBOL(blk_rq_unmap_kern_sg);
>>> +
>>> +static int blk_rq_handle_align_tail_only(struct request *rq,
>>> + struct scatterlist *sg_to_copy,
>>> + gfp_t gfp, gfp_t page_gfp)
>>> +{
>>> + int res = 0;
>>> + struct scatterlist *tail_sg = sg_to_copy;
>>> + struct scatterlist *new_sg;
>>> + struct scatterlist *hdr;
>>> + int new_sg_nents;
>>> + struct page *pg;
>>> +
>>> + new_sg_nents = 2;
>>> +
>>> + new_sg = kmalloc(sizeof(*new_sg) * new_sg_nents, gfp);
>>> + if (new_sg == NULL)
>>> + goto out_nomem;
>>> +
>>> + sg_init_table(new_sg, new_sg_nents);
>>> +
>>> + hdr = new_sg;
>>> + new_sg++;
>>> + new_sg_nents--;
>>> +
>>> + hdr->page_link = (unsigned long)tail_sg;
>>> + *new_sg = *tail_sg;
>>> +
>>> + pg = alloc_pages(page_gfp, get_order(tail_sg->length));
>>> + if (pg == NULL)
>>> + goto err_free_new_sg;
>>> +
>>> + if (rq_data_dir(rq) == WRITE) {
>>> + void *saddr, *daddr;
>>> + saddr = kmap_atomic(sg_page(tail_sg), KM_USER0) +
>>> + tail_sg->offset;
>>> + daddr = kmap_atomic(pg, KM_USER1);
>>> + memcpy(daddr, saddr, tail_sg->length);
>>> + kunmap_atomic(saddr, KM_USER0);
>>> + kunmap_atomic(daddr, KM_USER1);
>>> + }
>>> +
>>> + sg_assign_page(tail_sg, pg);
>>> + tail_sg->offset = 0;
>>> +
>>> + rq->end_io_data = hdr;
>>> + rq->cmd_flags |= REQ_HAS_TAIL_SPACE_FOR_PADDING;
>>> +
>>> +out:
>>> + return res;
>>> +
>>> +err_free_new_sg:
>>> + kfree(new_sg);
>>> +
>>> +out_nomem:
>>> + res = -ENOMEM;
>>> + goto out;
>>> +}
>>> +
>>> +static int blk_rq_handle_align(struct request *rq, struct scatterlist **psgl,
>>> + int *pnents, struct scatterlist *sgl_to_copy,
>>> + int nents_to_copy, gfp_t gfp, gfp_t page_gfp)
>>> +{
>>> + int res = 0, i;
>>> + struct scatterlist *sgl = *psgl;
>>> + int nents = *pnents;
>>> + struct scatterlist *sg, *prev_sg;
>>> + struct scatterlist *new_sgl;
>>> + struct scatterlist *hdr;
>>> + size_t len = 0, to_copy;
>>> + int new_sgl_nents, new_sgl_nents_to_alloc, n;
>>> +
>> below should use the sg_alloc_table / sg_free_table constructs for
>> the proper chaining/setting of scatterlist chains. Failing to do so
>> is both a code duplication and hinder of future changes to these constructs.
>> see all places that use sg_alloc_table/sg_free_table in source like scsi_lib.c.
>
> Done. I didn't know about sg_alloc_table()/sg_free_table().
>
>> I'll stop the review here. You need to solve the req->end_io_data use and change
>> this to sg_alloc_table/sg_free_table (perhaps the one with the callback i'm not sure)
>>
>> I'll continue review on the next patchset.
>
> Thanks!
> Vlad
>
I will go head and review your new patch
Boaz
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