target: Add target_submit_cmd() for process context fabric submission

This patch adds a target_submit_cmd() caller that can be used by fabrics
to submit an uninitialized se_cmd descriptor to an struct se_session +
unpacked_lun from workqueue process context.  This call will invoke the
following steps:

- transport_init_se_cmd() to setup se_cmd specific pointers
- Obtain se_cmd->cmd_kref references with target_get_sess_cmd()
- set se_cmd->t_tasks_bidi
- transport_lookup_cmd_lun() to setup struct se_cmd->se_lun from
  the passed unpacked_lun
- transport_generic_allocate_tasks() to setup the passed *cdb, and
- transport_handle_cdb_direct() handle READ dispatch or WRITE
  ready-to-transfer callback to fabric

v2 changes from hch feedback:

*) Add target_sc_flags_table for target_submit_cmd flags
*) Rename bidi parameter to flags, add TARGET_SCF_BIDI_OP
*) Convert checks to BUG_ON
*) Add out_check_cond for transport_send_check_condition_and_sense
   usage

v3 changes:

*) Add TARGET_SCF_ACK_KREF for target_submit_cmd into
   target_get_sess_cmd to determine when the fabric caller is expecting
   a second kref_put() from fabric packet acknowledgement.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

3 files changed, 92 insertions, 3 deletions

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 176f956665e..e4389d40c05 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1642,6 +1642,80 @@ int transport_handle_cdb_direct(
 }
 EXPORT_SYMBOL(transport_handle_cdb_direct);
 
+/**
+ * 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
+ *
+ * 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,
+                unsigned char *cdb, unsigned char *sense, u32 unpacked_lun,
+                u32 data_length, int task_attr, int data_dir, int flags)
+{
+        struct se_portal_group *se_tpg;
+        int rc;
+
+        se_tpg = se_sess->se_tpg;
+        BUG_ON(!se_tpg);
+        BUG_ON(se_cmd->se_tfo || se_cmd->se_sess);
+        BUG_ON(in_interrupt());
+        /*
+         * Initialize se_cmd for target operation.  From this point
+         * exceptions are handled by sending exception status via
+         * target_core_fabric_ops->queue_status() callback
+         */
+        transport_init_se_cmd(se_cmd, se_tpg->se_tpg_tfo, se_sess,
+                                data_length, data_dir, task_attr, sense);
+        /*
+         * Obtain struct se_cmd->cmd_kref reference and add new cmd to
+         * se_sess->sess_cmd_list.  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.
+         */
+        target_get_sess_cmd(se_sess, se_cmd, (flags & TARGET_SCF_ACK_KREF));
+        /*
+         * Signal bidirectional data payloads to target-core
+         */
+        if (flags & TARGET_SCF_BIDI_OP)
+                se_cmd->se_cmd_flags |= SCF_BIDI;
+        /*
+         * Locate se_lun pointer and attach it to struct se_cmd
+         */
+        if (transport_lookup_cmd_lun(se_cmd, unpacked_lun) < 0)
+                goto out_check_cond;
+        /*
+         * Sanitize CDBs via transport_generic_cmd_sequencer() and
+         * allocate the necessary tasks to complete the received CDB+data
+         */
+        rc = transport_generic_allocate_tasks(se_cmd, cdb);
+        if (rc != 0)
+                goto out_check_cond;
+        /*
+         * Dispatch se_cmd descriptor to se_lun->lun_se_dev backend
+         * for immediate execution of READs, otherwise wait for
+         * transport_generic_handle_data() to be called for WRITEs
+         * when fabric has filled the incoming buffer.
+         */
+        transport_handle_cdb_direct(se_cmd);
+        return 0;
+
+out_check_cond:
+        transport_send_check_condition_and_sense(se_cmd,
+                                se_cmd->scsi_sense_reason, 0);
+        return 0;
+}
+EXPORT_SYMBOL(target_submit_cmd);
+
 /*
  * Used by fabric module frontends defining a TFO->new_cmd_map() caller
  * to  queue up a newly setup se_cmd w/ TRANSPORT_NEW_CMD_MAP in order to
@@ -3910,13 +3984,21 @@ EXPORT_SYMBOL(transport_generic_free_cmd);
 /* target_get_sess_cmd - Add command to active ->sess_cmd_list
  * @se_sess:    session to reference
  * @se_cmd:     command descriptor to add
+ * @ack_kref:   Signal that fabric will perform an ack target_put_sess_cmd()
  */
-void target_get_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cmd)
+void target_get_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cmd,
+                        bool ack_kref)
 {
         unsigned long flags;
 
         kref_init(&se_cmd->cmd_kref);
-        kref_get(&se_cmd->cmd_kref);
+        /*
+         * Add a second kref if the fabric caller is expecting to handle
+         * fabric acknowledgement that requires two target_put_sess_cmd()
+         * invocations before se_cmd descriptor release.
+         */
+        if (ack_kref == true)
+                kref_get(&se_cmd->cmd_kref);
 
         spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
         list_add_tail(&se_cmd->se_cmd_list, &se_sess->sess_cmd_list);
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index af088a9e490..28190dc10ee 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -226,6 +226,11 @@ enum tcm_sense_reason_table {
         TCM_RESERVATION_CONFLICT                = 0x10,
 };
 
+enum target_sc_flags_table {
+        TARGET_SCF_BIDI_OP              = 0x01,
+        TARGET_SCF_ACK_KREF             = 0x02,
+};
+
 /* fabric independent task management function values */
 enum tcm_tmreq_table {
         TMR_ABORT_TASK          = 1,
diff --git a/include/target/target_core_fabric.h b/include/target/target_core_fabric.h
index d035d865dbe..aaa26da5a52 100644
--- a/include/target/target_core_fabric.h
+++ b/include/target/target_core_fabric.h
@@ -118,6 +118,8 @@ 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     transport_generic_allocate_tasks(struct se_cmd *, unsigned char *);
+int     target_submit_cmd(struct se_cmd *, struct se_session *, unsigned char *,
+                unsigned char *, u32, u32, int, int, int);
 int     transport_handle_cdb_direct(struct se_cmd *);
 int     transport_generic_handle_cdb_map(struct se_cmd *);
 int     transport_generic_handle_data(struct se_cmd *);
@@ -134,7 +136,7 @@ bool	transport_wait_for_tasks(struct se_cmd *);
 int     transport_check_aborted_status(struct se_cmd *, int);
 int     transport_send_check_condition_and_sense(struct se_cmd *, u8, int);
 
-void    target_get_sess_cmd(struct se_session *, struct se_cmd *);
+void    target_get_sess_cmd(struct se_session *, struct se_cmd *, bool);
 int     target_put_sess_cmd(struct se_session *, struct se_cmd *);
 void    target_splice_sess_cmd_list(struct se_session *);
 void    target_wait_for_sess_cmds(struct se_session *, int);