[PATCH 2/3] SG: Convert SCSI to use scatterlist helpers for sg chaining

[Boaz Harrosh <bharrosh@panasas.com>]

From: Jens Axboe <jens.axboe@oracle.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 drivers/scsi/libsrp.c        |    2 +-
 drivers/scsi/scsi_error.c    |    4 +-
 drivers/scsi/scsi_lib.c      |  150 +++++-------------------------------------
 drivers/usb/storage/isd200.c |    4 +-
 include/scsi/scsi_cmnd.h     |    9 +--
 5 files changed, 24 insertions(+), 145 deletions(-)

diff --git a/drivers/scsi/libsrp.c b/drivers/scsi/libsrp.c
index 8a8562a..b81350d 100644
--- a/drivers/scsi/libsrp.c
+++ b/drivers/scsi/libsrp.c
@@ -427,7 +427,7 @@ int srp_cmd_queue(struct Scsi_Host *shost, struct srp_cmd *cmd, void *info,
 	sc->SCp.ptr = info;
 	memcpy(sc->cmnd, cmd->cdb, MAX_COMMAND_SIZE);
 	sc->sdb.length = len;
-	sc->sdb.sglist = (void *) (unsigned long) addr;
+	sc->sdb.sgt.sgl = (void *) (unsigned long) addr;
 	sc->tag = tag;
 	err = scsi_tgt_queue_command(sc, itn_id, (struct scsi_lun *)&cmd->lun,
 				     cmd->tag);
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 5c8ba6a..1fd2a8c 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -629,9 +629,9 @@ void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
 		                       sizeof(scmd->sense_buffer), sense_bytes);
 		sg_init_one(&ses->sense_sgl, scmd->sense_buffer,
 							      scmd->sdb.length);
-		scmd->sdb.sglist = &ses->sense_sgl;
+		scmd->sdb.sgt.sgl = &ses->sense_sgl;
 		scmd->sc_data_direction = DMA_FROM_DEVICE;
-		scmd->sdb.sg_count = 1;
+		scmd->sdb.sgt.nents = 1;
 		memset(scmd->cmnd, 0, sizeof(scmd->cmnd));
 		scmd->cmnd[0] = REQUEST_SENSE;
 		scmd->cmnd[4] = scmd->sdb.length;
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a6aae56..c7107f1 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -750,136 +750,15 @@ static inline unsigned int scsi_sgtable_index(unsigned short nents)
 	return index;
 }
 
-static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb,
-					unsigned short sg_count, gfp_t gfp_mask)
+static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
 {
-	struct scsi_host_sg_pool *sgp;
-	struct scatterlist *sgl, *prev, *ret;
-	unsigned int index;
-	int this, left;
-
-	left = sg_count;
-	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;
-
-		sg_init_table(sgl, sgp->size);
-
-		/*
-		 * first loop through, set initial index and return value
-		 */
-		if (!ret)
-			ret = sgl;
-
-		/*
-		 * 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);
-
-		/*
-		 * if we have nothing left, mark the last segment as
-		 * end-of-list
-		 */
-		if (!left)
-			sg_mark_end(&sgl[this - 1]);
-
-		/*
-		 * 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.
-	 */
-	sdb->alloc_sg_count = sdb->sg_count = sg_count;
-	sdb->sglist = ret;
-	return 0;
-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 -ENOMEM;
+	return mempool_alloc(scsi_sg_pools[scsi_sgtable_index(nents)].pool,
+								    gfp_mask);
 }
 
-static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
+static void scsi_sg_free(struct scatterlist *sgl, unsigned int nents)
 {
-	struct scatterlist *sgl = sdb->sglist;
-	struct scsi_host_sg_pool *sgp;
-
-	/*
-	 * if this is the biggest size sglist, check if we have
-	 * chained parts we need to free
-	 */
-	if (sdb->alloc_sg_count > SCSI_MAX_SG_SEGMENTS) {
-		unsigned short this, left;
-		struct scatterlist *next;
-		unsigned int index;
-
-		left = sdb->alloc_sg_count - (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 = sdb->sglist;
-		sgp = scsi_sg_pools + SG_MEMPOOL_NR - 1;
-	} else
-		sgp = scsi_sg_pools + scsi_sgtable_index(sdb->alloc_sg_count);
-
-	mempool_free(sgl, sgp->pool);
+	mempool_free(sgl, scsi_sg_pools[scsi_sgtable_index(nents)].pool);
 }
 
 /*
@@ -901,15 +780,15 @@ static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
  */
 void scsi_release_buffers(struct scsi_cmnd *cmd)
 {
-	if (cmd->sdb.sglist)
-		scsi_free_sgtable(&cmd->sdb);
+	if (cmd->sdb.sgt.sgl)
+		__sg_free_table(&cmd->sdb.sgt, scsi_sg_free);
 
 	memset(&cmd->sdb, 0, sizeof(cmd->sdb));
 
 	if (scsi_bidi_cmnd(cmd)) {
 		struct scsi_data_buffer *bidi_sdb =
 			cmd->request->next_rq->special;
-		scsi_free_sgtable(bidi_sdb);
+		__sg_free_table(&bidi_sdb->sgt, scsi_sg_free);
 		kmem_cache_free(scsi_bidi_sdb_cache, bidi_sdb);
 		cmd->request->next_rq->special = NULL;
 	}
@@ -1135,9 +1014,12 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
 								 gfp_t gfp_mask)
 {
-	int count;
+	int count, ret;
 
-	if (scsi_alloc_sgtable(sdb, req->nr_phys_segments, gfp_mask)) {
+	ret = __sg_alloc_table(&sdb->sgt, req->nr_phys_segments, gfp_mask,
+								 scsi_sg_alloc);
+	if (unlikely(ret)) {
+		__sg_free_table(&sdb->sgt, scsi_sg_free);
 		return BLKPREP_DEFER;
 	}
 
@@ -1151,9 +1033,9 @@ static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
 	 * Next, walk the list, and fill in the addresses and sizes of
 	 * each segment.
 	 */
-	count = blk_rq_map_sg(req->q, req, sdb->sglist);
-	BUG_ON(count > sdb->sg_count);
-	sdb->sg_count = count;
+	count = blk_rq_map_sg(req->q, req, sdb->sgt.sgl);
+	BUG_ON(count > sdb->sgt.nents);
+	sdb->sgt.nents = count;
 	return BLKPREP_OK;
 }
 
diff --git a/drivers/usb/storage/isd200.c b/drivers/usb/storage/isd200.c
index 2d9a32b..0214ddb 100644
--- a/drivers/usb/storage/isd200.c
+++ b/drivers/usb/storage/isd200.c
@@ -415,9 +415,9 @@ static void isd200_set_srb(struct isd200_info *info,
 		sg_init_one(&info->sg, buff, bufflen);
 
 	srb->sc_data_direction = dir;
-	srb->sdb.sglist = buff ? &info->sg : NULL;
+	srb->sdb.sgt.sgl = buff ? &info->sg : NULL;
 	srb->sdb.length = bufflen;
-	srb->sdb.sg_count = buff ? 1 : 0;
+	srb->sdb.sgt.nents = buff ? 1 : 0;
 }
 
 static void isd200_srb_set_bufflen(struct scsi_cmnd *srb, unsigned bufflen)
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index cd2851a..9933bbe 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -8,16 +8,13 @@
 #include <linux/timer.h>
 #include <linux/scatterlist.h>
 
-struct scatterlist;
 struct Scsi_Host;
 struct scsi_device;
 
 struct scsi_data_buffer {
-	struct scatterlist *sglist;
+	struct sg_table sgt;
 	unsigned length;
 	int resid;
-	unsigned short sg_count;
-	unsigned short alloc_sg_count; /* private to scsi_lib */
 };
 
 /* embedded in scsi_cmnd */
@@ -136,12 +133,12 @@ extern void scsi_dma_unmap(struct scsi_cmnd *cmd);
 
 static inline unsigned scsi_sg_count(struct scsi_cmnd *cmd)
 {
-	return cmd->sdb.sg_count;
+	return cmd->sdb.sgt.nents;
 }
 
 static inline struct scatterlist *scsi_sglist(struct scsi_cmnd *cmd)
 {
-	return cmd->sdb.sglist;
+	return cmd->sdb.sgt.sgl;
 }
 
 static inline unsigned scsi_bufflen(struct scsi_cmnd *cmd)
-- 
1.5.3.3