[PATCH 2/7] Change scsi_cmnd.prot_sdb from a pointer into a regular member

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This patch slightly increases the size of struct scsi_cmnd if data
protection is disabled, decreases the size of the data appended at
the end of struct scsi_cmnd if data protection is enabled and
simplifies the SCSI core.

Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 drivers/scsi/scsi_lib.c  | 33 ++++++++++++---------------------
 include/scsi/scsi_cmnd.h |  8 ++++----
 2 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 94842b104bcc..6bfbe50ef38e 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -566,7 +566,7 @@ static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
 			sg_free_table_chained(&sdb->table, true);
 	}
 	if (scsi_prot_sg_count(cmd))
-		sg_free_table_chained(&cmd->prot_sdb->table, true);
+		sg_free_table_chained(&cmd->prot_sdb.table, true);
 }
 
 static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
@@ -1065,10 +1065,10 @@ blk_status_t scsi_init_io(struct scsi_cmnd *cmd)
 	}
 
 	if (blk_integrity_rq(rq)) {
-		struct scsi_data_buffer *prot_sdb = cmd->prot_sdb;
+		struct scsi_data_buffer *prot_sdb = &cmd->prot_sdb;
 		int ivecs, count;
 
-		if (WARN_ON_ONCE(!prot_sdb)) {
+		if (WARN_ON_ONCE(!scsi_host_get_prot(cmd->device->host))) {
 			/*
 			 * This can happen if someone (e.g. multipath)
 			 * queues a command to a device on an adapter
@@ -1091,8 +1091,7 @@ blk_status_t scsi_init_io(struct scsi_cmnd *cmd)
 		BUG_ON(count > ivecs);
 		BUG_ON(count > queue_max_integrity_segments(rq->q));
 
-		cmd->prot_sdb = prot_sdb;
-		cmd->prot_sdb->table.nents = count;
+		prot_sdb->table.nents = count;
 	}
 
 	return BLK_STS_OK;
@@ -1156,7 +1155,6 @@ void scsi_del_cmd_from_list(struct scsi_cmnd *cmd)
 void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
 {
 	void *buf = cmd->sense_buffer;
-	void *prot = cmd->prot_sdb;
 	struct request *rq = blk_mq_rq_from_pdu(cmd);
 	unsigned int flags = cmd->flags & SCMD_PRESERVED_FLAGS;
 	unsigned long jiffies_at_alloc;
@@ -1175,7 +1173,6 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
 
 	cmd->device = dev;
 	cmd->sense_buffer = buf;
-	cmd->prot_sdb = prot;
 	cmd->flags = flags;
 	INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
 	cmd->jiffies_at_alloc = jiffies_at_alloc;
@@ -1617,12 +1614,13 @@ static blk_status_t scsi_mq_prep_fn(struct request *req)
 	sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt->cmd_size;
 	cmd->sdb.table.sgl = sg;
 
-	if (scsi_host_get_prot(shost)) {
-		memset(cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));
-
-		cmd->prot_sdb->table.sgl =
-			(struct scatterlist *)(cmd->prot_sdb + 1);
-	}
+	/*
+	 * Always initialize cmd->prot_sdb.nents such that
+	 * scsi_prot_sg_count() does not have to call scsi_host_get_prot().
+	 */
+	memset(&cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));
+	if (scsi_host_get_prot(shost))
+		cmd->prot_sdb.table.sgl = (void *)&sg + scsi_mq_sgl_size(shost);
 
 	if (blk_bidi_rq(req)) {
 		struct request *next_rq = req->next_rq;
@@ -1781,7 +1779,6 @@ static int scsi_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
 	struct Scsi_Host *shost = set->driver_data;
 	const bool unchecked_isa_dma = shost->unchecked_isa_dma;
 	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
-	struct scatterlist *sg;
 
 	if (unchecked_isa_dma)
 		cmd->flags |= SCMD_UNCHECKED_ISA_DMA;
@@ -1791,12 +1788,6 @@ static int scsi_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
 		return -ENOMEM;
 	cmd->req.sense = cmd->sense_buffer;
 
-	if (scsi_host_get_prot(shost)) {
-		sg = (void *)cmd + sizeof(struct scsi_cmnd) +
-			shost->hostt->cmd_size;
-		cmd->prot_sdb = (void *)sg + scsi_mq_sgl_size(shost);
-	}
-
 	return 0;
 }
 
@@ -1893,7 +1884,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	sgl_size = scsi_mq_sgl_size(shost);
 	cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
 	if (scsi_host_get_prot(shost))
-		cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;
+		cmd_size += sgl_size;
 
 	memset(&shost->tag_set, 0, sizeof(shost->tag_set));
 	shost->tag_set.ops = &scsi_mq_ops;
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index d85e6befa26b..0406c0fbee3e 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -108,7 +108,7 @@ struct scsi_cmnd {
 
 	/* These elements define the operation we ultimately want to perform */
 	struct scsi_data_buffer sdb;
-	struct scsi_data_buffer *prot_sdb;
+	struct scsi_data_buffer prot_sdb;
 
 	unsigned underflow;	/* Return error if less than
 				   this amount is transferred */
@@ -318,17 +318,17 @@ static inline unsigned int scsi_prot_interval(struct scsi_cmnd *scmd)
 
 static inline unsigned scsi_prot_sg_count(struct scsi_cmnd *cmd)
 {
-	return cmd->prot_sdb ? cmd->prot_sdb->table.nents : 0;
+	return cmd->prot_sdb.table.nents;
 }
 
 static inline struct scatterlist *scsi_prot_sglist(struct scsi_cmnd *cmd)
 {
-	return cmd->prot_sdb ? cmd->prot_sdb->table.sgl : NULL;
+	return cmd->prot_sdb.table.sgl;
 }
 
 static inline struct scsi_data_buffer *scsi_prot(struct scsi_cmnd *cmd)
 {
-	return cmd->prot_sdb;
+	return &cmd->prot_sdb;
 }
 
 #define scsi_for_each_prot_sg(cmd, sg, nseg, __i)		\
-- 
2.20.1.321.g9e740568ce-goog




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