scsi: target: core: Break up target_submit_cmd_map_sgls()

This breaks up target_submit_cmd_map_sgls() into 3 helpers:

 - target_init_cmd(): Do the basic general setup and get a refcount to the
   session to make sure the caller can execute the cmd.

 - target_submit_prep(): Do the mapping, cdb processing and get a ref to
   the LUN.

 - target_submit(): Pass the cmd to LIO core for execution.

The above functions must be used by drivers that either:

 1. Rely on LIO for session shutdown synchronization by calling
    target_stop_session().

 2. Need to map sgls.

When the next patches are applied then simple drivers that do not need the
extra functionality above can use target_submit_cmd() and not worry about
failures being returned and how to handle them, since many drivers were
getting this wrong and would have hit refcount bugs.

Also, by breaking target_submit_cmd_map_sgls() up into these 3 helper
functions, we can allow the later patches to do the init/prep from
interrupt context and then do the submission from a workqueue.

Link: https://lore.kernel.org/r/20210227170006.5077-5-michael.christie@oracle.com
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Nilesh Javali <njavali@marvell.com>
Cc: Michael Cyr <mikecyr@linux.ibm.com>
Cc: Chris Boot <bootc@bootc.net>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_transport.c

@@ -1573,46 +1573,31 @@ transport_generic_map_mem_to_cmd(struct se_cmd *cmd, struct scatterlist *sgl,
 }
 
 /**
- * target_submit_cmd_map_sgls - lookup unpacked lun and submit uninitialized
- * 			 se_cmd + use pre-allocated SGL memory.
- *
- * @se_cmd: command descriptor to submit
+ * target_init_cmd - initialize se_cmd
+ * @se_cmd: command descriptor to init
  * @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_attr: 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
- * @sgl_prot: struct scatterlist memory protection information
- * @sgl_prot_count: scatterlist count for protection information
  *
  * Task tags are supported if the caller has set @se_cmd->tag.
  *
- * 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.
+ * Returns:
+ *	- less than zero to signal active I/O shutdown failure.
+ *	- zero on success.
  *
- * This may only be called from process context, and also currently
- * assumes internal allocation of fabric payload buffer by target-core.
+ * If the fabric driver calls target_stop_session, then it must check the
+ * return code and handle failures. This will never fail for other drivers,
+ * and the return code can be ignored.
  */
-int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess,
-		unsigned char *cdb, unsigned char *sense, u64 unpacked_lun,
-		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 scatterlist *sgl_prot, u32 sgl_prot_count)
+int target_init_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
+		    unsigned char *sense, u64 unpacked_lun,
+		    u32 data_length, int task_attr, int data_dir, int flags)
 {
 	struct se_portal_group *se_tpg;
-	sense_reason_t rc;
-	int ret;
-
-	might_sleep();
 
 	se_tpg = se_sess->se_tpg;
 	BUG_ON(!se_tpg);
@@ -1620,53 +1605,69 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 
 	if (flags & TARGET_SCF_USE_CPUID)
 		se_cmd->se_cmd_flags |= SCF_USE_CPUID;
+	/*
+	 * Signal bidirectional data payloads to target-core
+	 */
+	if (flags & TARGET_SCF_BIDI_OP)
+		se_cmd->se_cmd_flags |= SCF_BIDI;
+
+	if (flags & TARGET_SCF_UNKNOWN_SIZE)
+		se_cmd->unknown_data_length = 1;
 	/*
 	 * Initialize se_cmd for target operation.  From this point
 	 * exceptions are handled by sending exception status via
 	 * target_core_fabric_ops->queue_status() callback
 	 */
-	__target_init_cmd(se_cmd, se_tpg->se_tpg_tfo, se_sess,
-			  data_length, data_dir, task_attr, sense,
-			  unpacked_lun);
+	__target_init_cmd(se_cmd, se_tpg->se_tpg_tfo, se_sess, data_length,
+			  data_dir, task_attr, sense, unpacked_lun);
 
-	if (flags & TARGET_SCF_UNKNOWN_SIZE)
-		se_cmd->unknown_data_length = 1;
 	/*
 	 * Obtain struct se_cmd->cmd_kref reference. A second kref_get here is
 	 * necessary for fabrics using TARGET_SCF_ACK_KREF that expect a second
 	 * kref_put() to happen during fabric packet acknowledgement.
 	 */
-	ret = target_get_sess_cmd(se_cmd, flags & TARGET_SCF_ACK_KREF);
-	if (ret)
-		return ret;
-	/*
-	 * Signal bidirectional data payloads to target-core
-	 */
-	if (flags & TARGET_SCF_BIDI_OP)
-		se_cmd->se_cmd_flags |= SCF_BIDI;
+	return target_get_sess_cmd(se_cmd, flags & TARGET_SCF_ACK_KREF);
+}
+EXPORT_SYMBOL_GPL(target_init_cmd);
+
+/**
+ * target_submit_prep - prepare cmd for submission
+ * @se_cmd: command descriptor to prep
+ * @cdb: pointer to SCSI CDB
+ * @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
+ * @sgl_prot: struct scatterlist memory protection information
+ * @sgl_prot_count: scatterlist count for protection information
+ *
+ * Returns:
+ *	- less than zero to signal failure.
+ *	- zero on success.
+ * If failure is returned, lio will the callers queue_status to complete
+ * the cmd.
+ */
+int target_submit_prep(struct se_cmd *se_cmd, unsigned char *cdb,
+		       struct scatterlist *sgl, u32 sgl_count,
+		       struct scatterlist *sgl_bidi, u32 sgl_bidi_count,
+		       struct scatterlist *sgl_prot, u32 sgl_prot_count)
+{
+	sense_reason_t rc;
 
 	rc = target_cmd_init_cdb(se_cmd, cdb);
-	if (rc) {
-		transport_send_check_condition_and_sense(se_cmd, rc, 0);
-		target_put_sess_cmd(se_cmd);
-		return 0;
-	}
+	if (rc)
+		goto send_cc_direct;
 
 	/*
 	 * Locate se_lun pointer and attach it to struct se_cmd
 	 */
 	rc = transport_lookup_cmd_lun(se_cmd);
-	if (rc) {
-		transport_send_check_condition_and_sense(se_cmd, rc, 0);
-		target_put_sess_cmd(se_cmd);
-		return 0;
-	}
+	if (rc)
+		goto send_cc_direct;
 
 	rc = target_cmd_parse_cdb(se_cmd);
-	if (rc != 0) {
-		transport_generic_request_failure(se_cmd, rc);
-		return 0;
-	}
+	if (rc != 0)
+		goto generic_fail;
 
 	/*
 	 * Save pointers for SGLs containing protection information,
@@ -1686,6 +1687,41 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 	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)
+			goto generic_fail;
+	}
+
+	return 0;
+
+send_cc_direct:
+	transport_send_check_condition_and_sense(se_cmd, rc, 0);
+	target_put_sess_cmd(se_cmd);
+	return -EIO;
+
+generic_fail:
+	transport_generic_request_failure(se_cmd, rc);
+	return -EIO;
+}
+EXPORT_SYMBOL_GPL(target_submit_prep);
+
+/**
+ * target_submit - perform final initialization and submit cmd to LIO core
+ * @se_cmd: command descriptor to submit
+ *
+ * target_submit_prep must have been called on the cmd, and this must be
+ * called from process context.
+ */
+void target_submit(struct se_cmd *se_cmd)
+{
+	struct scatterlist *sgl = se_cmd->t_data_sg;
+	unsigned char *buf = NULL;
+
+	might_sleep();
+
+	if (se_cmd->t_data_nents != 0) {
+		BUG_ON(!sgl);
 		/*
 		 * A work-around for tcm_loop as some userspace code via
 		 * scsi-generic do not memset their associated read buffers,
@@ -1696,8 +1732,6 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 		 */
 		if (!(se_cmd->se_cmd_flags & SCF_SCSI_DATA_CDB) &&
 		     se_cmd->data_direction == DMA_FROM_DEVICE) {
-			unsigned char *buf = NULL;
-
 			if (sgl)
 				buf = kmap(sg_page(sgl)) + sgl->offset;
 
@@ -1707,12 +1741,6 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 			}
 		}
 
-		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, rc);
-			return 0;
-		}
 	}
 
 	/*
@@ -1722,6 +1750,57 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 	core_alua_check_nonop_delay(se_cmd);
 
 	transport_handle_cdb_direct(se_cmd);
+}
+EXPORT_SYMBOL_GPL(target_submit);
+
+/**
+ * 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
+ * @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_attr: 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
+ * @sgl_prot: struct scatterlist memory protection information
+ * @sgl_prot_count: scatterlist count for protection information
+ *
+ * Task tags are supported if the caller has set @se_cmd->tag.
+ *
+ * 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.
+ */
+int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess,
+		unsigned char *cdb, unsigned char *sense, u64 unpacked_lun,
+		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 scatterlist *sgl_prot, u32 sgl_prot_count)
+{
+	int rc;
+
+	rc = target_init_cmd(se_cmd, se_sess, sense, unpacked_lun,
+			     data_length, task_attr, data_dir, flags);
+	if (rc < 0)
+		return rc;
+
+	if (target_submit_prep(se_cmd, cdb, sgl, sgl_count, sgl_bidi,
+			       sgl_bidi_count, sgl_prot, sgl_prot_count))
+		return 0;
+
+	target_submit(se_cmd);
 	return 0;
 }
 EXPORT_SYMBOL(target_submit_cmd_map_sgls);

include/target/target_core_fabric.h

@@ -151,6 +151,14 @@ void	transport_deregister_session(struct se_session *);
 void	__target_init_cmd(struct se_cmd *,
 		const struct target_core_fabric_ops *,
 		struct se_session *, u32, int, int, unsigned char *, u64);
+int	target_init_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
+		unsigned char *sense, u64 unpacked_lun, u32 data_length,
+		int task_attr, int data_dir, int flags);
+int	target_submit_prep(struct se_cmd *se_cmd, unsigned char *cdb,
+		struct scatterlist *sgl, u32 sgl_count,
+		struct scatterlist *sgl_bidi, u32 sgl_bidi_count,
+		struct scatterlist *sgl_prot, u32 sgl_prot_count);
+void	target_submit(struct se_cmd *se_cmd);
 sense_reason_t transport_lookup_cmd_lun(struct se_cmd *);
 sense_reason_t target_cmd_init_cdb(struct se_cmd *, unsigned char *);
 sense_reason_t target_cmd_parse_cdb(struct se_cmd *);