target: Eliminate usage of struct se_mem

Both backstores and fabrics use arrays of struct scatterlist to describe
data buffers. However TCM used struct se_mems, basically a linked list
of scatterlist entries. We are able to simplify the code by eliminating
this intermediate data structure and just using struct scatterlist[]
throughout.

Also, moved attachment of task to cmd out of transport_generic_get_task
and into allocate_control_task and allocate_data_tasks. The reasoning
is that it's nonintuitive that get_task should automatically add it to
the cmd's task list -- it should just return an allocated, initialized
task. That's all it should do, based on the function's name, so either the
function shouldn't do it, or the name should change to encapsulate the
entire essence of what it does.

(nab: Fix compile warnings in tcm_fc, and make transport_kmap_first_data_page
 honor sg->offset for SGLs from contigious memory with TCM_Loop, and
 fix control se_cmd descriptor memory leak)

Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 26 insertions, 32 deletions

diff --git a/drivers/target/tcm_fc/tfc_io.c b/drivers/target/tcm_fc/tfc_io.c
index 837660728563..3563a9029c4a 100644
--- a/drivers/target/tcm_fc/tfc_io.c
+++ b/drivers/target/tcm_fc/tfc_io.c
@@ -68,17 +68,17 @@ int ft_queue_data_in(struct se_cmd *se_cmd)
 	struct fc_frame *fp = NULL;
 	struct fc_exch *ep;
 	struct fc_lport *lport;
-	struct se_mem *mem;
+	struct scatterlist *sg = NULL;
 	size_t remaining;
 	u32 f_ctl = FC_FC_EX_CTX | FC_FC_REL_OFF;
-	u32 mem_off;
+	u32 mem_off = 0;
 	u32 fh_off = 0;
 	u32 frame_off = 0;
 	size_t frame_len = 0;
-	size_t mem_len;
+	size_t mem_len = 0;
 	size_t tlen;
 	size_t off_in_page;
-	struct page *page;
+	struct page *page = NULL;
 	int use_sg;
 	int error;
 	void *page_addr;
@@ -94,13 +94,12 @@ int ft_queue_data_in(struct se_cmd *se_cmd)
 	/*
 	 * Setup to use first mem list entry, unless no data.
 	 */
-	BUG_ON(remaining && list_empty(&se_cmd->t_mem_list));
+	BUG_ON(remaining && !se_cmd->t_data_sg);
 	if (remaining) {
-		mem = list_first_entry(&se_cmd->t_mem_list,
-			 struct se_mem, se_list);
-		mem_len = mem->se_len;
-		mem_off = mem->se_off;
-		page = mem->se_page;
+		sg = se_cmd->t_data_sg;
+		mem_len = sg->length;
+		mem_off = sg->offset;
+		page = sg_page(sg);
 	}
 
 	/* no scatter/gather in skb for odd word length due to fc_seq_send() */
@@ -108,12 +107,10 @@ int ft_queue_data_in(struct se_cmd *se_cmd)
 
 	while (remaining) {
 		if (!mem_len) {
-			BUG_ON(!mem);
-			mem = list_entry(mem->se_list.next,
-				struct se_mem, se_list);
-			mem_len = min((size_t)mem->se_len, remaining);
-			mem_off = mem->se_off;
-			page = mem->se_page;
+			sg = sg_next(sg);
+			mem_len = min((size_t)sg->length, remaining);
+			mem_off = sg->offset;
+			page = sg_page(sg);
 		}
 		if (!frame_len) {
 			/*
@@ -200,13 +197,13 @@ void ft_recv_write_data(struct ft_cmd *cmd, struct fc_frame *fp)
 	struct fc_exch *ep;
 	struct fc_lport *lport;
 	struct fc_frame_header *fh;
-	struct se_mem *mem;
-	u32 mem_off;
+	struct scatterlist *sg = NULL;
+	u32 mem_off = 0;
 	u32 rel_off;
 	size_t frame_len;
-	size_t mem_len;
+	size_t mem_len = 0;
 	size_t tlen;
-	struct page *page;
+	struct page *page = NULL;
 	void *page_addr;
 	void *from;
 	void *to;
@@ -288,23 +285,20 @@ void ft_recv_write_data(struct ft_cmd *cmd, struct fc_frame *fp)
 	/*
 	 * Setup to use first mem list entry, unless no data.
 	 */
-	BUG_ON(frame_len && list_empty(&se_cmd->t_mem_list));
+	BUG_ON(frame_len && !se_cmd->t_data_sg);
 	if (frame_len) {
-		mem = list_first_entry(&se_cmd->t_mem_list,
-				       struct se_mem, se_list);
-		mem_len = mem->se_len;
-		mem_off = mem->se_off;
-		page = mem->se_page;
+		sg = se_cmd->t_data_sg;
+		mem_len = sg->length;
+		mem_off = sg->offset;
+		page = sg_page(sg);
 	}
 
 	while (frame_len) {
 		if (!mem_len) {
-			BUG_ON(!mem);
-			mem = list_entry(mem->se_list.next,
-					 struct se_mem, se_list);
-			mem_len = mem->se_len;
-			mem_off = mem->se_off;
-			page = mem->se_page;
+			sg = sg_next(sg);
+			mem_len = sg->length;
+			mem_off = sg->offset;
+			page = sg_page(sg);
 		}
 		if (rel_off >= mem_len) {
 			rel_off -= mem_len;