iscsi-target: Add iscsit_transport API template

Add basic struct iscsit_transport API template to allow iscsi-target for
running with external transport modules using existing iscsi_target_core.h
code.

For all external modules, this calls try_module_get() and module_put()
to obtain + release an external iscsit_transport module reference count.

Also include the iscsi-target symbols necessary in iscsi_transport.h to
allow external transport modules to function.

v3 changes:
- Add iscsit_build_reject export for ISTATE_SEND_REJECT usage

v2 changes:

- Drop unnecessary export of iscsit_get_transport + iscsit_put_transport (roland)
- Add ->iscsit_queue_data_in() to remove extra context switch on RDMA_WRITE
- Add ->iscsit_queue_status() to remove extra context switch on IB_SEND status
- Add ->iscsit_get_dataout() to remove extra context switch on RDMA_READ
- Drop ->iscsit_free_cmd()
- Drop ->iscsit_unmap_cmd()
- Rename iscsit_create_transport() -> iscsit_register_transport() (andy)
- Rename iscsit_destroy_transport() -> iscsit_unregister_transport() (andy)

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

1 files changed, 55 insertions, 0 deletions

diff --git a/drivers/target/iscsi/iscsi_target_transport.c b/drivers/target/iscsi/iscsi_target_transport.c
new file mode 100644
index 000000000000..882728fac30c
--- /dev/null
+++ b/drivers/target/iscsi/iscsi_target_transport.c
@@ -0,0 +1,55 @@
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <target/iscsi/iscsi_transport.h>
+
+static LIST_HEAD(g_transport_list);
+static DEFINE_MUTEX(transport_mutex);
+
+struct iscsit_transport *iscsit_get_transport(int type)
+{
+	struct iscsit_transport *t;
+
+	mutex_lock(&transport_mutex);
+	list_for_each_entry(t, &g_transport_list, t_node) {
+		if (t->transport_type == type) {
+			if (t->owner && !try_module_get(t->owner)) {
+				t = NULL;
+			}
+			mutex_unlock(&transport_mutex);
+			return t;
+		}
+	}
+	mutex_unlock(&transport_mutex);
+
+	return NULL;
+}
+
+void iscsit_put_transport(struct iscsit_transport *t)
+{
+	if (t->owner)
+		module_put(t->owner);
+}
+
+int iscsit_register_transport(struct iscsit_transport *t)
+{
+	INIT_LIST_HEAD(&t->t_node);
+
+	mutex_lock(&transport_mutex);
+	list_add_tail(&t->t_node, &g_transport_list);
+	mutex_unlock(&transport_mutex);
+
+	pr_debug("Registered iSCSI transport: %s\n", t->name);
+
+	return 0;
+}
+EXPORT_SYMBOL(iscsit_register_transport);
+
+void iscsit_unregister_transport(struct iscsit_transport *t)
+{
+	mutex_lock(&transport_mutex);
+	list_del(&t->t_node);
+	mutex_unlock(&transport_mutex);
+
+	pr_debug("Unregistered iSCSI transport: %s\n", t->name);
+}
+EXPORT_SYMBOL(iscsit_unregister_transport);