target: Remove transport_do_task_sg_chain() and associated detritus

Now that all fabrics are converted over to using se_cmd->t_data_sg
directly, we can drop the task sg chaining support.  With the modern
memory allocation in target core, task sg chaining is needless
overhead -- we would split up the main cmd sglist into pieces, and
then splice those pieces back together instead of just using the
original list directly.

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

drivers/target/target_core_transport.c

@@ -3699,76 +3699,6 @@ static inline sector_t transport_limit_task_sectors(
 	return sectors;
 }
 
-
-/*
- * This function can be used by HW target mode drivers to create a linked
- * scatterlist from all contiguously allocated struct se_task->task_sg[].
- * This is intended to be called during the completion path by TCM Core
- * when struct target_core_fabric_ops->check_task_sg_chaining is enabled.
- */
-void transport_do_task_sg_chain(struct se_cmd *cmd)
-{
-	struct scatterlist *sg_first = NULL;
-	struct scatterlist *sg_prev = NULL;
-	int sg_prev_nents = 0;
-	struct scatterlist *sg;
-	struct se_task *task;
-	u32 chained_nents = 0;
-	int i;
-
-	BUG_ON(!cmd->se_tfo->task_sg_chaining);
-
-	/*
-	 * Walk the struct se_task list and setup scatterlist chains
-	 * for each contiguously allocated struct se_task->task_sg[].
-	 */
-	list_for_each_entry(task, &cmd->t_task_list, t_list) {
-		if (!task->task_sg)
-			continue;
-
-		if (!sg_first) {
-			sg_first = task->task_sg;
-			chained_nents = task->task_sg_nents;
-		} else {
-			sg_chain(sg_prev, sg_prev_nents, task->task_sg);
-			chained_nents += task->task_sg_nents;
-		}
-		/*
-		 * For the padded tasks, use the extra SGL vector allocated
-		 * in transport_allocate_data_tasks() for the sg_prev_nents
-		 * offset into sg_chain() above.
-		 *
-		 * We do not need the padding for the last task (or a single
-		 * task), but in that case we will never use the sg_prev_nents
-		 * value below which would be incorrect.
-		 */
-		sg_prev_nents = (task->task_sg_nents + 1);
-		sg_prev = task->task_sg;
-	}
-	/*
-	 * Setup the starting pointer and total t_tasks_sg_linked_no including
-	 * padding SGs for linking and to mark the end.
-	 */
-	cmd->t_tasks_sg_chained = sg_first;
-	cmd->t_tasks_sg_chained_no = chained_nents;
-
-	pr_debug("Setup cmd: %p cmd->t_tasks_sg_chained: %p and"
-		" t_tasks_sg_chained_no: %u\n", cmd, cmd->t_tasks_sg_chained,
-		cmd->t_tasks_sg_chained_no);
-
-	for_each_sg(cmd->t_tasks_sg_chained, sg,
-			cmd->t_tasks_sg_chained_no, i) {
-
-		pr_debug("SG[%d]: %p page: %p length: %d offset: %d\n",
-			i, sg, sg_page(sg), sg->length, sg->offset);
-		if (sg_is_chain(sg))
-			pr_debug("SG: %p sg_is_chain=1\n", sg);
-		if (sg_is_last(sg))
-			pr_debug("SG: %p sg_is_last=1\n", sg);
-	}
-}
-EXPORT_SYMBOL(transport_do_task_sg_chain);
-
 /*
  * Break up cmd into chunks transport can handle
  */

include/target/target_core_base.h

@@ -572,7 +572,6 @@ struct se_cmd {
 	unsigned char		*t_task_cdb;
 	unsigned char		__t_task_cdb[TCM_MAX_COMMAND_SIZE];
 	unsigned long long	t_task_lba;
-	u32			t_tasks_sg_chained_no;
 	atomic_t		t_fe_count;
 	atomic_t		t_se_count;
 	atomic_t		t_task_cdbs_left;
@@ -593,7 +592,6 @@ struct se_cmd {
 	struct completion	t_transport_stop_comp;
 	struct completion	transport_lun_fe_stop_comp;
 	struct completion	transport_lun_stop_comp;
-	struct scatterlist	*t_tasks_sg_chained;
 
 	struct work_struct	work;
 

include/target/target_core_fabric.h

@@ -3,12 +3,6 @@
 
 struct target_core_fabric_ops {
 	struct configfs_subsystem *tf_subsys;
-	/*
-	 * Optional to signal struct se_task->task_sg[] padding entries
-	 * for scatterlist chaining using transport_do_task_sg_link(),
-	 * disabled by default
-	 */
-	bool task_sg_chaining;
 	char *(*get_fabric_name)(void);
 	u8 (*get_fabric_proto_ident)(struct se_portal_group *);
 	char *(*tpg_get_wwn)(struct se_portal_group *);
@@ -124,7 +118,6 @@ int	transport_generic_handle_cdb_map(struct se_cmd *);
 int	transport_generic_handle_data(struct se_cmd *);
 int	transport_generic_map_mem_to_cmd(struct se_cmd *cmd,
 		struct scatterlist *, u32, struct scatterlist *, u32);
-void	transport_do_task_sg_chain(struct se_cmd *);
 int	transport_generic_new_cmd(struct se_cmd *);
 
 void	transport_generic_process_write(struct se_cmd *);