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@oracle.com>

3 files changed, 24 insertions, 124 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 4cf902efbdbf..3b5121c4c081 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -739,138 +739,41 @@ 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;
+        sgp = scsi_sg_pools + scsi_sgtable_index(nents);
+        mempool_free(sgl, sgp->pool);
+}
 
-                sgl = mempool_alloc(sgp->pool, gfp_mask);
-                if (unlikely(!sgl))
-                        goto enomem;
+static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
+{
+        struct scsi_host_sg_pool *sgp;
 
-                sg_init_table(sgl, sgp->size);
+        sgp = scsi_sg_pools + scsi_sgtable_index(nents);
+        return mempool_alloc(sgp->pool, gfp_mask);
+}
 
-                /*
-                 * first loop through, set initial index and return value
-                 */
-                if (!ret)
-                        ret = sgl;
+int scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+{
+        int ret;
 
-                /*
-                 * 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);
+        BUG_ON(!cmd->use_sg);
 
-                /*
-                 * if we have nothing left, mark the last segment as
-                 * end-of-list
-                 */
-                if (!left)
-                        sg_mark_end(&sgl[this - 1]);
+        ret = __sg_alloc_table(&cmd->sg_table, cmd->use_sg, gfp_mask, scsi_sg_alloc);
+        if (unlikely(ret))
+                __sg_free_table(&cmd->sg_table, scsi_sg_free);
 
-                /*
-                 * 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);
-
-        /*
-         * ->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);
 
 void scsi_free_sgtable(struct scsi_cmnd *cmd)
 {
-        struct scatterlist *sgl = cmd->request_buffer;
-        struct scsi_host_sg_pool *sgp;
-
-        /*
-         * if this is the biggest size sglist, check if we have
-         * chained parts we need to free
-         */
-        if (cmd->__use_sg > SCSI_MAX_SG_SEGMENTS) {
-                unsigned short this, left;
-                struct scatterlist *next;
-                unsigned int index;
-
-                left = cmd->__use_sg - (SCSI_MAX_SG_SEGMENTS - 1);
-                next = sg_chain_ptr(&sgl[SCSI_MAX_SG_SEGMENTS - 1]);
-                while (left && next) {
-                        sgl = next;
-                        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;
-
-                        if (left)
-                                next = sg_chain_ptr(&sgl[sgp->size - 1]);
-
-                        mempool_free(sgl, sgp->pool);
-                }
-
-                /*
-                 * Restore original, will be freed below
-                 */
-                sgl = cmd->request_buffer;
-                sgp = scsi_sg_pools + SG_MEMPOOL_NR - 1;
-        } else
-                sgp = scsi_sg_pools + scsi_sgtable_index(cmd->__use_sg);
-
-        mempool_free(sgl, sgp->pool);
+        __sg_free_table(&cmd->sg_table, scsi_sg_free);
 }
 
 EXPORT_SYMBOL(scsi_free_sgtable);
@@ -1120,8 +1023,7 @@ static int scsi_init_io(struct scsi_cmnd *cmd)
         /*
          * If sg table allocation fails, requeue request later.
          */
-        cmd->request_buffer = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
-        if (unlikely(!cmd->request_buffer)) {
+        if (unlikely(scsi_alloc_sgtable(cmd, GFP_ATOMIC))) {
                 scsi_unprep_request(req);
                 return BLKPREP_DEFER;
         }
diff --git a/drivers/scsi/scsi_tgt_lib.c b/drivers/scsi/scsi_tgt_lib.c
index 93ece8f4e5de..01e03f3f6ffa 100644
--- a/drivers/scsi/scsi_tgt_lib.c
+++ b/drivers/scsi/scsi_tgt_lib.c
@@ -359,8 +359,7 @@ static int scsi_tgt_init_cmd(struct scsi_cmnd *cmd, gfp_t gfp_mask)
         int count;
 
         cmd->use_sg = rq->nr_phys_segments;
-        cmd->request_buffer = scsi_alloc_sgtable(cmd, gfp_mask);
-        if (!cmd->request_buffer)
+        if (scsi_alloc_sgtable(cmd, gfp_mask))
                 return -ENOMEM;
 
         cmd->request_bufflen = rq->data_len;
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index abd7479ff452..a457fca66f61 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -8,7 +8,6 @@
 #include <linux/scatterlist.h>
 
 struct request;
-struct scatterlist;
 struct Scsi_Host;
 struct scsi_device;
 
@@ -68,8 +67,8 @@ struct scsi_cmnd {
         void *request_buffer;           /* Actual requested buffer */
 
         /* These elements define the operation we ultimately want to perform */
+        struct sg_table sg_table;
         unsigned short use_sg;  /* Number of pieces of scatter-gather */
-        unsigned short __use_sg;
 
         unsigned underflow;     /* Return error if less than
                                    this amount is transferred */
@@ -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);
 extern void scsi_free_sgtable(struct scsi_cmnd *);
 
 extern int scsi_dma_map(struct scsi_cmnd *cmd);
 extern void scsi_dma_unmap(struct scsi_cmnd *cmd);
 
 #define scsi_sg_count(cmd) ((cmd)->use_sg)
-#define scsi_sglist(cmd) ((struct scatterlist *)(cmd)->request_buffer)
+#define scsi_sglist(cmd) ((cmd)->sg_table.sgl)
 #define scsi_bufflen(cmd) ((cmd)->request_bufflen)
 
 static inline void scsi_set_resid(struct scsi_cmnd *cmd, int resid)