Re: [PATCH v2]: New implementation of scsi_execute_async()

[Boaz Harrosh]

On 07/14/2009 07:17 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.
> 
> 4. When needed, copy_page() is used instead of memcpy() to copy the whole pages.
> 
> Also this patch adds and exports functions sg_copy() and sg_copy_elem(), which
> cop one SG to another and one SG element to another respectively.
> 
> 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@xxxxxxxx>
> 
>  block/blk-map.c             |  408 ++++++++++++++++++++++++++++++++++++++++++++
>  drivers/scsi/scsi_lib.c     |  108 +++++++++++
>  include/linux/blkdev.h      |    3 
>  include/linux/scatterlist.h |    7 
>  include/scsi/scsi_device.h  |   11 +
>  lib/scatterlist.c           |  147 +++++++++++++++
>  6 files changed, 683 insertions(+), 1 deletion(-)
> 
> 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	2009-07-10 21:13:25.000000000 +0400
> +++ linux-2.6.30.1/block/blk-map.c	2009-07-14 19:24:36.000000000 +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"
> @@ -272,6 +273,413 @@ int blk_rq_unmap_user(struct bio *bio)
>  }
>  EXPORT_SYMBOL(blk_rq_unmap_user);
>  
> +struct blk_kern_sg_hdr {
> +	struct scatterlist *orig_sgp;
> +	union {
> +		struct sg_table new_sg_table;
> +		struct scatterlist *saved_sg;
> +	};

There is a struct scatterlist * inside struct sg_table
just use that. No need for a union. (It's not like your saving
space). In the tail case nents == 1.
(orig_nents==0 and loose the tail_only)

> +	bool tail_only;
> +};
> +
> +#define BLK_KERN_SG_HDR_ENTRIES	(1 + (sizeof(struct blk_kern_sg_hdr) - 1) / \
> +				 sizeof(struct scatterlist))
> +
> +/**
> + * 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)
+void blk_rq_unmap_kern_sg(struct request *req, struct blk_kern_sg_hdr *hdr, int do_copy)

> +{
> +	struct blk_kern_sg_hdr *hdr = (struct blk_kern_sg_hdr *)req->end_io_data;
> +

Again still req->end_io_data can not be used. You can add a pointer to the call
or use/add another member.

> +	if (hdr == NULL)
> +		goto out;
> +
> +	if (hdr->tail_only) {
> +		/* Tail element only was copied */
> +		struct scatterlist *saved_sg = hdr->saved_sg;
> +		struct scatterlist *tail_sg = hdr->orig_sgp;
> +
> +		if ((rq_data_dir(req) == READ) && do_copy)
> +			sg_copy_elem(saved_sg, tail_sg, tail_sg->length,
> +				KM_BIO_DST_IRQ, KM_BIO_SRC_IRQ);
> +
> +		__free_pages(sg_page(tail_sg), get_order(tail_sg->length));
> +		*tail_sg = *saved_sg;
> +		kfree(hdr);
> +	} else {
> +		/* The whole SG was copied */
> +		struct sg_table new_sg_table = hdr->new_sg_table;
> +		struct scatterlist *new_sgl = new_sg_table.sgl +
> +						BLK_KERN_SG_HDR_ENTRIES;
> +		struct scatterlist *orig_sgl = hdr->orig_sgp;
> +
> +		if ((rq_data_dir(req) == READ) && do_copy)
> +			sg_copy(orig_sgl, new_sgl, 0, KM_BIO_DST_IRQ,
> +				KM_BIO_SRC_IRQ);
> +
> +		sg_free_table(&new_sg_table);
> +	}
> +
> +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 *saved_sg;
> +	struct blk_kern_sg_hdr *hdr;
> +	int saved_sg_nents;
> +	struct page *pg;
> +
> +	saved_sg_nents = 1 + BLK_KERN_SG_HDR_ENTRIES;
> +
> +	saved_sg = kmalloc(sizeof(*saved_sg) * saved_sg_nents, gfp);
> +	if (saved_sg == NULL)
> +		goto out_nomem;
> +
> +	sg_init_table(saved_sg, saved_sg_nents);
> +
> +	hdr = (struct blk_kern_sg_hdr *)saved_sg;
> +	saved_sg += BLK_KERN_SG_HDR_ENTRIES;
> +	saved_sg_nents -= BLK_KERN_SG_HDR_ENTRIES;
> +
> +	hdr->tail_only = true;
> +	hdr->orig_sgp = tail_sg;
> +	hdr->saved_sg = saved_sg;
> +
> +	*saved_sg = *tail_sg;
> +
> +	pg = alloc_pages(page_gfp, get_order(tail_sg->length));
> +	if (pg == NULL)
> +		goto err_free_saved_sg;
> +
> +	sg_assign_page(tail_sg, pg);
> +	tail_sg->offset = 0;
> +
> +	if (rq_data_dir(rq) == WRITE)
> +		sg_copy_elem(tail_sg, saved_sg, saved_sg->length,
> +				KM_USER1, KM_USER0);
> +
> +	rq->end_io_data = hdr;

Perhaps return it to the user or pass an **void output
parameter to be set, or again another member

> +	rq->cmd_flags |= REQ_HAS_TAIL_SPACE_FOR_PADDING;
> +
> +out:
> +	return res;
> +
> +err_free_saved_sg:
> +	kfree(saved_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 sg_table sg_table;
> +	struct scatterlist *sg;
> +	struct scatterlist *new_sgl;
> +	size_t len = 0, to_copy;
> +	int new_sgl_nents;
> +	struct blk_kern_sg_hdr *hdr;
> +
> +	if (sgl != sgl_to_copy) {
> +		/* copy only the last element */
> +		res = blk_rq_handle_align_tail_only(rq, sgl_to_copy,
> +				gfp, page_gfp);
> +		if (res == 0)
> +			goto out;
> +		/* else go through */
> +	}
> +
> +	for_each_sg(sgl, sg, nents, i)
> +		len += sg->length;
> +	to_copy = len;
> +
> +	new_sgl_nents = PFN_UP(len) + BLK_KERN_SG_HDR_ENTRIES;
> +
> +	res = sg_alloc_table(&sg_table, new_sgl_nents, gfp);
> +	if (res != 0)
> +		goto out;
> +
> +	new_sgl = sg_table.sgl;
> +	hdr = (struct blk_kern_sg_hdr *)new_sgl;
> +	new_sgl += BLK_KERN_SG_HDR_ENTRIES;
> +	new_sgl_nents -= BLK_KERN_SG_HDR_ENTRIES;
> +
> +	hdr->tail_only = false;
> +	hdr->orig_sgp = sgl;
> +	hdr->new_sg_table = sg_table;
> +
> +	for_each_sg(new_sgl, sg, new_sgl_nents, i) {
> +		struct page *pg;
> +
> +		pg = alloc_page(page_gfp);
> +		if (pg == NULL)
> +			goto err_free_new_sgl;
> +
> +		sg_assign_page(sg, pg);
> +		sg->length = min_t(size_t, PAGE_SIZE, len);
> +
> +		len -= PAGE_SIZE;
> +	}
> +
> +	if (rq_data_dir(rq) == WRITE) {
> +		/*
> +		 * We need to limit amount of copied data to to_copy, because
> +		 * sgl might have the last element not marked as last in
> +		 * SG chaining.
> +		 */
> +		sg_copy(new_sgl, sgl, to_copy, KM_USER0, KM_USER1);
> +	}
> +
> +	rq->end_io_data = hdr;
> +	rq->cmd_flags |= REQ_HAS_TAIL_SPACE_FOR_PADDING;
> +
> +	*psgl = new_sgl;
> +	*pnents = new_sgl_nents;
> +
> +out:
> +	return res;
> +
> +err_free_new_sgl:
> +	for_each_sg(new_sgl, sg, new_sgl_nents, i) {
> +		struct page *pg = sg_page(sg);
> +		if (pg == NULL)
> +			break;
> +		__free_page(pg);
> +	}
> +	sg_free_table(&sg_table);
> +
> +	res = -ENOMEM;
> +	goto out;
> +}
> +
> +static void bio_map_kern_endio(struct bio *bio, int err)
> +{
> +	bio_put(bio);
> +}
> +
> +static int __blk_rq_map_kern_sg(struct request *rq, struct scatterlist *sgl,
> +	int nents, gfp_t gfp, struct scatterlist **sgl_to_copy,
> +	int *nents_to_copy)
> +{
> +	int res;
> +	struct request_queue *q = rq->q;
> +	int rw = rq_data_dir(rq);
> +	int max_nr_vecs, i;
> +	size_t tot_len;
> +	bool need_new_bio;
> +	struct scatterlist *sg, *prev_sg = NULL;
> +	struct bio *bio = NULL, *hbio = NULL, *tbio = NULL;
> +
> +	*sgl_to_copy = NULL;
> +
> +	if (unlikely((sgl == 0) || (nents <= 0))) {
> +		WARN_ON(1);
> +		res = -EINVAL;
> +		goto out;
> +	}
> +
> +	/*
> +	 * Let's keep each bio allocation inside a single page to decrease
> +	 * probability of failure.
> +	 */
> +	max_nr_vecs =  min_t(size_t,
> +		((PAGE_SIZE - sizeof(struct bio)) / sizeof(struct bio_vec)),
> +		BIO_MAX_PAGES);
> +
> +	need_new_bio = true;
> +	tot_len = 0;
> +	for_each_sg(sgl, sg, nents, i) {
> +		struct page *page = sg_page(sg);
> +		void *page_addr = page_address(page);
> +		size_t len = sg->length, l;
> +		size_t offset = sg->offset;
> +
> +		tot_len += len;
> +		prev_sg = sg;
> +
> +		/*
> +		 * Each segment must be aligned on DMA boundary and
> +		 * not on stack. The last one may have unaligned
> +		 * length as long as the total length is aligned to
> +		 * DMA padding alignment.
> +		 */
> +		if (i == nents - 1)
> +			l = 0;
> +		else
> +			l = len;
> +		if (((sg->offset | l) & queue_dma_alignment(q)) ||
> +		    (page_addr && object_is_on_stack(page_addr + sg->offset))) {
> +			res = -EINVAL;
> +			goto out_need_copy;
> +		}
> +
> +		while (len > 0) {
> +			size_t bytes;
> +			int rc;
> +
> +			if (need_new_bio) {
> +				bio = bio_kmalloc(gfp, max_nr_vecs);
> +				if (bio == NULL) {
> +					res = -ENOMEM;
> +					goto out_free_bios;
> +				}
> +
> +				if (rw == WRITE)
> +					bio->bi_rw |= 1 << BIO_RW;
> +
> +				bio->bi_end_io = bio_map_kern_endio;
> +
> +				if (hbio == NULL)
> +					hbio = tbio = bio;
> +				else
> +					tbio = tbio->bi_next = bio;
> +			}
> +
> +			bytes = min_t(size_t, len, PAGE_SIZE - offset);
> +
> +			rc = bio_add_pc_page(q, bio, page, bytes, offset);
> +			if (rc < bytes) {
> +				if (unlikely(need_new_bio || (rc < 0))) {
> +					if (rc < 0)
> +						res = rc;
> +					else
> +						res = -EIO;
> +					goto out_need_copy;
> +				} else {
> +					need_new_bio = true;
> +					len -= rc;
> +					offset += rc;
> +					continue;
> +				}
> +			}
> +
> +			need_new_bio = false;
> +			offset = 0;
> +			len -= bytes;
> +			page = nth_page(page, 1);
> +		}
> +	}
> +
> +	if (hbio == NULL) {
> +		res = -EINVAL;
> +		goto out_free_bios;
> +	}
> +
> +	/* Total length must be aligned on DMA padding alignment */
> +	if ((tot_len & q->dma_pad_mask) &&
> +	    !(rq->cmd_flags & REQ_HAS_TAIL_SPACE_FOR_PADDING)) {
> +		res = -EINVAL;
> +		if (sgl->offset == 0) {
> +			*sgl_to_copy = prev_sg;
> +			*nents_to_copy = 1;
> +			goto out_free_bios;
> +		} else
> +			goto out_need_copy;
> +	}
> +
> +	while (hbio != NULL) {
> +		bio = hbio;
> +		hbio = hbio->bi_next;
> +		bio->bi_next = NULL;
> +
> +		blk_queue_bounce(q, &bio);

I do not understand. If you are bouncing on the bio level.
why do you need to do all the alignment checks and
sg-bouncing + tail handling all this is done again on the bio
level.

It looks to me that perhaps you did not understand Tejun's code
His code, as I remember, was on the bio level, but here you
are duplicating what is done in bio level.

But maybe I don't understand. Tejun?

> +
> +		res = blk_rq_append_bio(q, rq, bio);
> +		if (unlikely(res != 0)) {
> +			bio->bi_next = hbio;
> +			hbio = bio;
> +			goto out_free_bios;
> +		}
> +	}
> +
> +	rq->buffer = rq->data = NULL;
> +
> +out:
> +	return res;
> +
> +out_need_copy:
> +	*sgl_to_copy = sgl;
> +	*nents_to_copy = nents;
> +
> +out_free_bios:
> +	while (hbio != NULL) {
> +		bio = hbio;
> +		hbio = hbio->bi_next;
> +		bio_put(bio);
> +	}
> +	goto out;
> +}
> +
> +/**
> + * blk_rq_map_kern_sg - map kernel data to a request, for REQ_TYPE_BLOCK_PC
> + * @rq:		request to fill
> + * @sgl:	area to map
> + * @nents:	number of elements in @sgl
> + * @gfp:	memory allocation flags
> + *
> + * Description:
> + *    Data will be mapped directly if possible. Otherwise a bounce
> + *    buffer will be used.
> + */
> +int blk_rq_map_kern_sg(struct request *rq, struct scatterlist *sgl,
> +		       int nents, gfp_t gfp)
> +{
> +	int res;
> +	struct scatterlist *sg_to_copy = NULL;
> +	int nents_to_copy = 0;
> +
> +	if (unlikely((sgl == 0) || (sgl->length == 0) ||
> +		     (nents <= 0) || (rq->end_io_data != NULL))) {
> +		WARN_ON(1);
> +		res = -EINVAL;
> +		goto out;
> +	}
> +
> +	res = __blk_rq_map_kern_sg(rq, sgl, nents, gfp, &sg_to_copy,
> +				&nents_to_copy);
> +	if (unlikely(res != 0)) {
> +		if (sg_to_copy == NULL)
> +			goto out;
> +
> +		res = blk_rq_handle_align(rq, &sgl, &nents, sg_to_copy,
> +				nents_to_copy, gfp, rq->q->bounce_gfp | gfp);
> +		if (unlikely(res != 0))
> +			goto out;
> +
> +		res = __blk_rq_map_kern_sg(rq, sgl, nents, gfp, &sg_to_copy,
> +						&nents_to_copy);
> +		if (res != 0) {
> +			blk_rq_unmap_kern_sg(rq, 0);
> +			goto out;
> +		}
> +	}
> +
> +	rq->buffer = rq->data = NULL;
> +
> +out:
> +	return res;
> +}
> +EXPORT_SYMBOL(blk_rq_map_kern_sg);
> +
>  /**
>   * blk_rq_map_kern - map kernel data to a request, for REQ_TYPE_BLOCK_PC usage
>   * @q:		request queue where request should be inserted
> diff -upkr linux-2.6.30.1/drivers/scsi/scsi_lib.c linux-2.6.30.1/drivers/scsi/scsi_lib.c
> --- linux-2.6.30.1/drivers/scsi/scsi_lib.c	2009-07-10 21:13:25.000000000 +0400
> +++ linux-2.6.30.1/drivers/scsi/scsi_lib.c	2009-07-08 21:24:29.000000000 +0400
> @@ -277,6 +277,100 @@ int scsi_execute_req(struct scsi_device 
>  }
>  EXPORT_SYMBOL(scsi_execute_req);
>  
> +struct scsi_io_context {
> +	void *blk_data;
> +	void *data;
> +	void (*done)(void *data, char *sense, int result, int resid);
> +	char sense[SCSI_SENSE_BUFFERSIZE];
> +};
> +
> +static struct kmem_cache *scsi_io_context_cache;
> +
> +static void scsi_end_async(struct request *req, int error)
> +{
> +	struct scsi_io_context *sioc = req->end_io_data;
> +
> +	req->end_io_data = sioc->blk_data;
> +	blk_rq_unmap_kern_sg(req, (error == 0));
> +
> +	if (sioc->done)
> +		sioc->done(sioc->data, sioc->sense, req->errors, req->data_len);
> +
> +	kmem_cache_free(scsi_io_context_cache, sioc);
> +	__blk_put_request(req->q, req);

There is nothing scsi here. Do it in the caller

> +}
> +
> +/**
> + * scsi_execute_async - insert request
> + * @sdev:	scsi device
> + * @cmd:	scsi command
> + * @cmd_len:	length of scsi cdb
> + * @data_direction: DMA_TO_DEVICE, DMA_FROM_DEVICE, or DMA_NONE
> + * @sgl:	data buffer scatterlist
> + * @nents:	number of elements in the sgl
> + * @timeout:	request timeout in seconds
> + * @retries:	number of times to retry request
> + * @privdata:	data passed to done()
> + * @done:	callback function when done
> + * @gfp:	memory allocation flags
> + * @flags:	one or more SCSI_ASYNC_EXEC_FLAG_* flags
> + */
> +int scsi_execute_async(struct scsi_device *sdev, const unsigned char *cmd,
> +		       int cmd_len, int data_direction, struct scatterlist *sgl,
> +		       int nents, int timeout, int retries, void *privdata,
> +		       void (*done)(void *, char *, int, int), gfp_t gfp,
> +		       int flags)
> +{
> +	struct request *req;
> +	struct scsi_io_context *sioc;
> +	int err = 0;
> +	int write = (data_direction == DMA_TO_DEVICE);
> +
> +	sioc = kmem_cache_zalloc(scsi_io_context_cache, gfp);
> +	if (sioc == NULL)
> +		return DRIVER_ERROR << 24;
> +
> +	req = blk_get_request(sdev->request_queue, write, gfp);
> +	if (req == NULL)
> +		goto free_sense;
> +	req->cmd_type = REQ_TYPE_BLOCK_PC;
> +	req->cmd_flags |= REQ_QUIET;
> +

Block API

> +	if (flags & SCSI_ASYNC_EXEC_FLAG_HAS_TAIL_SPACE_FOR_PADDING)
> +		req->cmd_flags |= REQ_HAS_TAIL_SPACE_FOR_PADDING;
> +
> +	if (sgl != NULL) {
> +		err = blk_rq_map_kern_sg(req, sgl, nents, gfp);
> +		if (err)
> +			goto free_req;
> +	}
> +

All block API nothing scsi here

> +	sioc->blk_data = req->end_io_data;
> +	sioc->data = privdata;
> +	sioc->done = done;
> +
> +	req->cmd_len = cmd_len;
> +	memset(req->cmd, 0, BLK_MAX_CDB); /* ATAPI hates garbage after CDB */
> +	memcpy(req->cmd, cmd, req->cmd_len);

Does not support large commands.
Also a blk API nothing scsi about it

> +	req->sense = sioc->sense;
> +	req->sense_len = 0;
> +	req->timeout = timeout;
> +	req->retries = retries;
> +	req->end_io_data = sioc;
> +
> +	blk_execute_rq_nowait(req->q, NULL, req,
> +		flags & SCSI_ASYNC_EXEC_FLAG_AT_HEAD, scsi_end_async);
> +	return 0;
> +
> +free_req:
> +	blk_put_request(req);
> +
> +free_sense:
> +	kmem_cache_free(scsi_io_context_cache, sioc);
> +	return DRIVER_ERROR << 24;
> +}
> +EXPORT_SYMBOL_GPL(scsi_execute_async);
> +

The complete scsi bits are not needed. They have nothing to do with
scsi. If at all this should go into black layer. 
scsi_lib is not a wrapper around blk API.

>  /*
>   * Function:    scsi_init_cmd_errh()
>   *
> @@ -1743,12 +1837,20 @@ int __init scsi_init_queue(void)
>  {
>  	int i;
>  
> +	scsi_io_context_cache = kmem_cache_create("scsi_io_context",
> +					sizeof(struct scsi_io_context),
> +					0, 0, NULL);
> +	if (!scsi_io_context_cache) {
> +		printk(KERN_ERR "SCSI: can't init scsi io context cache\n");
> +		return -ENOMEM;
> +	}
> +
>  	scsi_sdb_cache = kmem_cache_create("scsi_data_buffer",
>  					   sizeof(struct scsi_data_buffer),
>  					   0, 0, NULL);
>  	if (!scsi_sdb_cache) {
>  		printk(KERN_ERR "SCSI: can't init scsi sdb cache\n");
> -		return -ENOMEM;
> +		goto cleanup_io_context;
>  	}
>  
>  	for (i = 0; i < SG_MEMPOOL_NR; i++) {
> @@ -1784,6 +1886,9 @@ cleanup_sdb:
>  	}
>  	kmem_cache_destroy(scsi_sdb_cache);
>  
> +cleanup_io_context:
> +	kmem_cache_destroy(scsi_io_context_cache);
> +
>  	return -ENOMEM;
>  }
>  
> @@ -1791,6 +1896,7 @@ void scsi_exit_queue(void)
>  {
>  	int i;
>  
> +	kmem_cache_destroy(scsi_io_context_cache);
>  	kmem_cache_destroy(scsi_sdb_cache);
>  
>  	for (i = 0; i < SG_MEMPOOL_NR; i++) {
> diff -upkr linux-2.6.30.1/include/linux/blkdev.h linux-2.6.30.1/include/linux/blkdev.h
> --- linux-2.6.30.1/include/linux/blkdev.h	2009-07-10 21:13:25.000000000 +0400
> +++ linux-2.6.30.1/include/linux/blkdev.h	2009-07-13 13:56:45.000000000 +0400
> @@ -807,6 +807,9 @@ extern int blk_rq_map_kern(struct reques
>  extern int blk_rq_map_user_iov(struct request_queue *, struct request *,
>  			       struct rq_map_data *, struct sg_iovec *, int,
>  			       unsigned int, gfp_t);
> +extern int blk_rq_map_kern_sg(struct request *rq,
> +			      struct scatterlist *sgl, int nents, gfp_t gfp);
> +extern void blk_rq_unmap_kern_sg(struct request *req, int do_copy);
>  extern int blk_execute_rq(struct request_queue *, struct gendisk *,
>  			  struct request *, int);
>  extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
> diff -upkr linux-2.6.30.1/include/linux/scatterlist.h linux-2.6.30.1/include/linux/scatterlist.h
> --- linux-2.6.30.1/include/linux/scatterlist.h	2009-06-10 07:05:27.000000000 +0400
> +++ linux-2.6.30.1/include/linux/scatterlist.h	2009-07-13 13:56:24.000000000 +0400
> @@ -218,6 +218,13 @@ size_t sg_copy_from_buffer(struct scatte
>  size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
>  			 void *buf, size_t buflen);
>  
> +int sg_copy_elem(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 sg_copy(struct scatterlist *dst_sg,
> +	    struct scatterlist *src_sg, size_t copy_len,
> +	    enum km_type d_km_type, enum km_type s_km_type);
> +
>  /*
>   * Maximum number of entries that will be allocated in one piece, if
>   * a list larger than this is required then chaining will be utilized.
> diff -upkr linux-2.6.30.1/include/scsi/scsi_device.h linux-2.6.30.1/include/scsi/scsi_device.h
> --- linux-2.6.30.1/include/scsi/scsi_device.h	2009-07-10 21:13:25.000000000 +0400
> +++ linux-2.6.30.1/include/scsi/scsi_device.h	2009-07-08 21:24:29.000000000 +0400
> @@ -372,6 +372,17 @@ extern int scsi_execute_req(struct scsi_
>  			    struct scsi_sense_hdr *, int timeout, int retries,
>  			    int *resid);
>  
> +#define SCSI_ASYNC_EXEC_FLAG_AT_HEAD			1
> +#define SCSI_ASYNC_EXEC_FLAG_HAS_TAIL_SPACE_FOR_PADDING	2
> +

Just use blk API directly inside the caller

> +#define SCSI_EXEC_REQ_FIFO_DEFINED
> +extern int scsi_execute_async(struct scsi_device *sdev, const unsigned char *cmd,
> +			      int cmd_len, int data_direction,
> +			      struct scatterlist *sgl, int nents, int timeout,
> +			      int retries, void *privdata,
> +			      void (*done)(void *, char *, int, int),
> +			      gfp_t gfp, int flags);
> +
>  static inline int __must_check scsi_device_reprobe(struct scsi_device *sdev)
>  {
>  	return device_reprobe(&sdev->sdev_gendev);
> diff -upkr linux-2.6.30.1/lib/scatterlist.c linux-2.6.30.1/lib/scatterlist.c
> --- linux-2.6.30.1/lib/scatterlist.c	2009-06-10 07:05:27.000000000 +0400
> +++ linux-2.6.30.1/lib/scatterlist.c	2009-07-14 19:22:49.000000000 +0400
> @@ -485,3 +485,150 @@ size_t sg_copy_to_buffer(struct scatterl
>  	return sg_copy_buffer(sgl, nents, buf, buflen, 1);
>  }
>  EXPORT_SYMBOL(sg_copy_to_buffer);
> +
> +/*
> + * Can switch to the next dst_sg element, so, to copy to strictly only
> + * one dst_sg element, it must be either last in the chain, or
> + * copy_len == dst_sg->length.
> + */
> +static int __sg_copy_elem(struct scatterlist **pdst_sg, size_t *pdst_len,
> +			  size_t *pdst_offs, struct scatterlist *src_sg,
> +			  size_t copy_len,
> +			  enum km_type d_km_type, enum km_type s_km_type)
> +{
> +	int res = 0;
> +	struct scatterlist *dst_sg;
> +	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_sg = *pdst_sg;
> +	dst_len = *pdst_len;
> +	dst_offs = *pdst_offs;
> +	dst_page = sg_page(dst_sg);
> +
> +	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 +
> +					 (src_offs >> PAGE_SHIFT), s_km_type) +
> +				    (src_offs & ~PAGE_MASK);
> +		daddr = kmap_atomic(dst_page +
> +					(dst_offs >> PAGE_SHIFT), d_km_type) +
> +				    (dst_offs & ~PAGE_MASK);
> +
> +		if (((src_offs & ~PAGE_MASK) == 0) &&
> +		    ((dst_offs & ~PAGE_MASK) == 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_MASK),
> +					  PAGE_SIZE - (src_offs & ~PAGE_MASK));
> +			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;
> +
> +		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);
> +
> +out:
> +	*pdst_sg = dst_sg;
> +	*pdst_len = dst_len;
> +	*pdst_offs = dst_offs;
> +	return res;
> +}
> +
> +/**
> + * sg_copy_elem - copy one SG element to another
> + * @dst_sg:	destination SG element
> + * @src_sg:	source SG element
> + * @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 source SG element will be copied to the destination SG
> + *    element. Returns number of bytes copied. Can switch to the next dst_sg
> + *    element, so, to copy to strictly only one dst_sg element, it must be
> + *    either last in the chain, or copy_len == dst_sg->length.
> + */
> +int sg_copy_elem(struct scatterlist *dst_sg, struct scatterlist *src_sg,
> +		 size_t copy_len, enum km_type d_km_type,
> +		 enum km_type s_km_type)
> +{
> +	size_t dst_len = dst_sg->length, dst_offs = dst_sg->offset;
> +
> +	return __sg_copy_elem(&dst_sg, &dst_len, &dst_offs, src_sg,
> +		copy_len, d_km_type, s_km_type);
> +}
> +EXPORT_SYMBOL(sg_copy_elem);

Is not sg_copy_elem a copy of an sg with one element. Why do we need
two exports.

I would pass a nents count to below and discard this one.

> +
> +/**
> + * sg_copy - 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 source SG vector will be copied to the destination SG
> + *    vector. End of the vectors will be determined by sg_next() returning
> + *    NULL. Returns number of bytes copied.
> + */
> +int sg_copy(struct scatterlist *dst_sg,
> +	    struct scatterlist *src_sg, size_t copy_len,

Total length is nice, but also a nents count

> +	    enum km_type d_km_type, enum km_type s_km_type)
> +{
> +	int res = 0;
> +	size_t dst_len, dst_offs;
> +
> +	if (copy_len == 0)
> +		copy_len = 0x7FFFFFFF; /* copy all */
> +
> +	dst_len = dst_sg->length;
> +	dst_offs = dst_sg->offset;
> +
> +	do {
> +		copy_len -= __sg_copy_elem(&dst_sg, &dst_len, &dst_offs,
> +				src_sg, copy_len, d_km_type, s_km_type);
> +		if ((copy_len == 0) || (dst_sg == NULL))
> +			goto out;
> +
> +		src_sg = sg_next(src_sg);
> +	} while (src_sg != NULL);
> +
> +out:
> +	return res;
> +}
> +EXPORT_SYMBOL(sg_copy);
> 

Boaz
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