On Nov. 14, 2007, 13:47 +0200, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
>>From 7b2421e1c075d3c262e28d0598608141add2e7da Mon Sep 17 00:00:00 2001
> From: Jens Axboe <jens.axboe@xxxxxxxxxx>
> Date: Wed, 14 Nov 2007 12:36:47 +0100
> Subject: [PATCH] SG: Convert SCSI to use scatterlist helpers for sg chaining
>
> Also change scsi_alloc_sgtable() to just return 0/failure, since it
> maps to the command passed in. ->request_buffer is now no longer needed,
> once drivers are adapted to use scsi_sglist() it can be killed.
>
> Signed-off-by: Jens Axboe <jens.axboe@xxxxxxxxxx>
> ---
> drivers/scsi/scsi_lib.c | 137 ++++++-------------------------------------
> drivers/scsi/scsi_tgt_lib.c | 3 +-
> include/scsi/scsi_cmnd.h | 7 +-
> 3 files changed, 23 insertions(+), 124 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 0e81e4c..1fb3c2e 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -737,138 +737,40 @@ static inline unsigned int scsi_sgtable_index(unsigned short nents)
> return index;
> }
>
> -struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
> +static void scsi_sg_free(struct scatterlist *sgl, unsigned int nents)
> {
> struct scsi_host_sg_pool *sgp;
> - struct scatterlist *sgl, *prev, *ret;
> - unsigned int index;
> - int this, left;
> -
> - BUG_ON(!cmd->use_sg);
> -
> - left = cmd->use_sg;
> - ret = prev = NULL;
> - do {
> - this = left;
> - if (this > SCSI_MAX_SG_SEGMENTS) {
> - this = SCSI_MAX_SG_SEGMENTS - 1;
> - index = SG_MEMPOOL_NR - 1;
> - } else
> - index = scsi_sgtable_index(this);
> -
> - left -= this;
>
> - sgp = scsi_sg_pools + index;
> -
> - sgl = mempool_alloc(sgp->pool, gfp_mask);
> - if (unlikely(!sgl))
> - goto enomem;
> + sgp = scsi_sg_pools + scsi_sgtable_index(nents);
> + mempool_free(sgl, sgp->pool);
> +}
>
> - sg_init_table(sgl, sgp->size);
> +static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
> +{
> + struct scsi_host_sg_pool *sgp;
>
> - /*
> - * first loop through, set initial index and return value
> - */
> - if (!ret)
> - ret = sgl;
> + sgp = scsi_sg_pools + scsi_sgtable_index(nents);
> + return mempool_alloc(sgp->pool, gfp_mask);
> +}
>
> - /*
> - * chain previous sglist, if any. we know the previous
> - * sglist must be the biggest one, or we would not have
> - * ended up doing another loop.
> - */
> - if (prev)
> - sg_chain(prev, SCSI_MAX_SG_SEGMENTS, sgl);
> +int scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
> +{
> + int ret;
>
> - /*
> - * if we have nothing left, mark the last segment as
> - * end-of-list
> - */
> - if (!left)
> - sg_mark_end(&sgl[this - 1]);
> + BUG_ON(!cmd->use_sg);
>
> - /*
> - * don't allow subsequent mempool allocs to sleep, it would
> - * violate the mempool principle.
> - */
> - gfp_mask &= ~__GFP_WAIT;
> - gfp_mask |= __GFP_HIGH;
> - prev = sgl;
> - } while (left);
> + ret = __sg_alloc_table(&cmd->sg_table, cmd->use_sg, gfp_mask,
> + scsi_sg_alloc, scsi_sg_free);
>
> - /*
> - * ->use_sg may get modified after dma mapping has potentially
> - * shrunk the number of segments, so keep a copy of it for free.
> - */
> - cmd->__use_sg = cmd->use_sg;
> + cmd->request_buffer = cmd->sg_table.sgl;
> return ret;
> -enomem:
> - if (ret) {
> - /*
> - * Free entries chained off ret. Since we were trying to
> - * allocate another sglist, we know that all entries are of
> - * the max size.
> - */
> - sgp = scsi_sg_pools + SG_MEMPOOL_NR - 1;
> - prev = ret;
> - ret = &ret[SCSI_MAX_SG_SEGMENTS - 1];
> -
> - while ((sgl = sg_chain_ptr(ret)) != NULL) {
> - ret = &sgl[SCSI_MAX_SG_SEGMENTS - 1];
> - mempool_free(sgl, sgp->pool);
> - }
> -
> - mempool_free(prev, sgp->pool);
> - }
> - return NULL;
> }
>
> EXPORT_SYMBOL(scsi_alloc_sgtable);
<snip>
> @@ -128,14 +127,14 @@ extern void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
> size_t *offset, size_t *len);
> extern void scsi_kunmap_atomic_sg(void *virt);
>
> -extern struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *, gfp_t);
> +extern int scsi_alloc_sgtable(struct scsi_cmnd *, gfp_t);
This becomes even nicer on top of the last sdb patches that Boaz sent:
http://www.spinics.net/lists/linux-scsi/msg20947.html
and
http://www.spinics.net/lists/linux-scsi/msg20948.html
that unexport this scsi_alloc_sgtable and make it look like this:
+static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb,
+ unsigned short sg_count, gfp_t gfp_mask)
-
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