target: Add transport_handle_cdb_direct optimization

This patch adds a transport_handle_cdb_direct() optimization for mapping
and queueing tasks directly from within fabric processing context by calling
the newly exported transport_generic_new_cmd().  This currently expects to
be called from process context only, and will fail if called within interrupt
context.

This patch also leaves transport_generic_handle_cdb() unmodified for the
moment to function as expected with existing tcm_fc and ib_srpt fabrics,
and will be removed once these have been converted and tested with v4.1
code using transport_handle_cdb_direct().

Based on Andy's original patch here:

[PATCH 39/42] target: Call transport_new_cmd instead of adding to cmd queue

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index d42a98e4725b..1ae6eb7a621b 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1842,12 +1842,36 @@ int transport_generic_handle_cdb(
                 printk(KERN_ERR "cmd->se_lun is NULL\n");
                 return -EINVAL;
         }
+
         transport_add_cmd_to_queue(cmd, TRANSPORT_NEW_CMD);
         return 0;
 }
 EXPORT_SYMBOL(transport_generic_handle_cdb);
 
 /*
+ * Used by fabric module frontends to queue tasks directly.
+ * Many only be used from process context only
+ */
+int transport_handle_cdb_direct(
+        struct se_cmd *cmd)
+{
+        if (!cmd->se_lun) {
+                dump_stack();
+                printk(KERN_ERR "cmd->se_lun is NULL\n");
+                return -EINVAL;
+        }
+        if (in_interrupt()) {
+                dump_stack();
+                printk(KERN_ERR "transport_generic_handle_cdb cannot be called"
+                                " from interrupt context\n");
+                return -EINVAL;
+        }
+
+        return transport_generic_new_cmd(cmd);
+}
+EXPORT_SYMBOL(transport_handle_cdb_direct);
+
+/*
  * 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
  * complete setup in TCM process context w/ TFO->new_cmd_map().