target: Add target_submit_cmd_map_sgls for SGL fabric memory passthrough

This patch adds a new target_submit_cmd_map_sgls() to pass pre-allocated
SGL memory using transport_generic_map_mem_to_cmd() logic into the generic
target submit I/O codepath.

It also adds a target_submit_cmd() wrapper around target_submit_cmd_map_sgls()
for existing fabric code that already assumes internal target-core SGL memory
allocation.

(v2: Rename to target_submit_cmd_map_sgls + drop TARGET_SCF_MAP_MEM flag
     in favor of non zero sgl_count check)
Reported-by: NChristoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -1455,8 +1455,9 @@ int transport_handle_cdb_direct(
 }
 EXPORT_SYMBOL(transport_handle_cdb_direct);
 
-/**
- * target_submit_cmd - lookup unpacked lun and submit uninitialized se_cmd
+/*
+ * target_submit_cmd_map_sgls - lookup unpacked lun and submit uninitialized
+ * 			 se_cmd + use pre-allocated SGL memory.
  *
  * @se_cmd: command descriptor to submit
  * @se_sess: associated se_sess for endpoint
@@ -1467,6 +1468,10 @@ EXPORT_SYMBOL(transport_handle_cdb_direct);
  * @task_addr: SAM task attribute
  * @data_dir: DMA data direction
  * @flags: flags for command submission from target_sc_flags_tables
+ * @sgl: struct scatterlist memory for unidirectional mapping
+ * @sgl_count: scatterlist count for unidirectional mapping
+ * @sgl_bidi: struct scatterlist memory for bidirectional READ mapping
+ * @sgl_bidi_count: scatterlist count for bidirectional READ mapping
  *
  * Returns non zero to signal active I/O shutdown failure.  All other
  * setup exceptions will be returned as a SCSI CHECK_CONDITION response,
@@ -1474,10 +1479,12 @@ EXPORT_SYMBOL(transport_handle_cdb_direct);
  *
  * This may only be called from process context, and also currently
  * assumes internal allocation of fabric payload buffer by target-core.
- **/
-int target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
+ */
+int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess,
 		unsigned char *cdb, unsigned char *sense, u32 unpacked_lun,
-		u32 data_length, int task_attr, int data_dir, int flags)
+		u32 data_length, int task_attr, int data_dir, int flags,
+		struct scatterlist *sgl, u32 sgl_count,
+		struct scatterlist *sgl_bidi, u32 sgl_bidi_count)
 {
 	struct se_portal_group *se_tpg;
 	int rc;
@@ -1524,7 +1531,21 @@ int target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
 		transport_generic_request_failure(se_cmd);
 		return 0;
 	}
-
+	/*
+	 * When a non zero sgl_count has been passed perform SGL passthrough
+	 * mapping for pre-allocated fabric memory instead of having target
+	 * core perform an internal SGL allocation..
+	 */
+	if (sgl_count != 0) {
+		BUG_ON(!sgl);
+
+		rc = transport_generic_map_mem_to_cmd(se_cmd, sgl, sgl_count,
+				sgl_bidi, sgl_bidi_count);
+		if (rc != 0) {
+			transport_generic_request_failure(se_cmd);
+			return 0;
+		}
+	}
 	/*
 	 * Check if we need to delay processing because of ALUA
 	 * Active/NonOptimized primary access state..
@@ -1534,6 +1555,38 @@ int target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
 	transport_handle_cdb_direct(se_cmd);
 	return 0;
 }
+EXPORT_SYMBOL(target_submit_cmd_map_sgls);
+
+/*
+ * target_submit_cmd - lookup unpacked lun and submit uninitialized se_cmd
+ *
+ * @se_cmd: command descriptor to submit
+ * @se_sess: associated se_sess for endpoint
+ * @cdb: pointer to SCSI CDB
+ * @sense: pointer to SCSI sense buffer
+ * @unpacked_lun: unpacked LUN to reference for struct se_lun
+ * @data_length: fabric expected data transfer length
+ * @task_addr: SAM task attribute
+ * @data_dir: DMA data direction
+ * @flags: flags for command submission from target_sc_flags_tables
+ *
+ * Returns non zero to signal active I/O shutdown failure.  All other
+ * setup exceptions will be returned as a SCSI CHECK_CONDITION response,
+ * but still return zero here.
+ *
+ * This may only be called from process context, and also currently
+ * assumes internal allocation of fabric payload buffer by target-core.
+ *
+ * It also assumes interal target core SGL memory allocation.
+ */
+int target_submit_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
+		unsigned char *cdb, unsigned char *sense, u32 unpacked_lun,
+		u32 data_length, int task_attr, int data_dir, int flags)
+{
+	return target_submit_cmd_map_sgls(se_cmd, se_sess, cdb, sense,
+			unpacked_lun, data_length, task_attr, data_dir,
+			flags, NULL, 0, NULL, 0);
+}
 EXPORT_SYMBOL(target_submit_cmd);
 
 static void target_complete_tmr_failure(struct work_struct *work)

include/target/target_core_fabric.h

@@ -100,6 +100,9 @@ void	transport_init_se_cmd(struct se_cmd *, struct target_core_fabric_ops *,
 		struct se_session *, u32, int, int, unsigned char *);
 int	transport_lookup_cmd_lun(struct se_cmd *, u32);
 int	target_setup_cmd_from_cdb(struct se_cmd *, unsigned char *);
+int	target_submit_cmd_map_sgls(struct se_cmd *, struct se_session *,
+		unsigned char *, unsigned char *, u32, u32, int, int, int,
+		struct scatterlist *, u32, struct scatterlist *, u32);
 int	target_submit_cmd(struct se_cmd *, struct se_session *, unsigned char *,
 		unsigned char *, u32, u32, int, int, int);
 int	target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,