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Subject[PATCH 2/6] tcm: Add support for struct target_core_fabric_ops->task_sg_chaining
Date
From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch adds support for struct target_core_fabric_ops->task_sg_chaining=1,
which allows a single struct se_cmd descriptor to use include/linux/scatterlist.h
SGL chaining logic and link contigious struct se_task->task_sg[] arrays together
into a single walkable scatterlist chain for HW target mode drivers that require
this for pci_map_sg().

This also includes a transport_do_task_sg_chain() helper which does the sg_chain()
calls, and other necessary struct scatterlist->page_link termination bit twiddling to
create a linked SGL from struct se_task->task_sg[] created in transport_calc_sg_num()

Inside of transport_calc_sg_num(), this patch when running in TFI->task_sg_chaining=1
mode will alloc an extra trailing padding struct scatterlist entry to the primary
struct se_task->task_sg[] allocation. The call to transport_do_task_sg_chain()
will then use these extra trailing SGL for the sg_chain() call.

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
drivers/target/target_core_transport.c | 127 +++++++++++++++++++++++++++++-
include/target/target_core_base.h | 4 +
include/target/target_core_fabric_ops.h | 6 ++
include/target/target_core_transport.h | 1 +
4 files changed, 133 insertions(+), 5 deletions(-)

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 5be102c..602b2d8 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -6736,7 +6736,8 @@ extern u32 transport_calc_sg_num(
{
struct se_cmd *se_cmd = task->task_se_cmd;
struct se_mem *se_mem = in_se_mem;
- u32 sg_length, task_size = task->task_size;
+ struct target_core_fabric_ops *tfo = CMD_TFO(se_cmd);
+ u32 sg_length, task_size = task->task_size, task_sg_num_padded;

while (task_size != 0) {
DEBUG_SC("se_mem->se_page(%p) se_mem->se_len(%u)"
@@ -6786,8 +6787,19 @@ next:

task->task_sg_num++;
}
+ /*
+ * Check if the fabric module driver is requesting that all
+ * struct se_task->task_sg[] be chained together.. If so,
+ * then allocate an extra padding SG entry for linking and
+ * marking the end of the chained SGL.
+ */
+ if (tfo->task_sg_chaining) {
+ task_sg_num_padded = (task->task_sg_num + 1);
+ task->task_padded_sg = 1;
+ } else
+ task_sg_num_padded = task->task_sg_num;

- task->task_sg = kzalloc(task->task_sg_num *
+ task->task_sg = kzalloc(task_sg_num_padded *
sizeof(struct scatterlist), GFP_KERNEL);
if (!(task->task_sg)) {
printk(KERN_ERR "Unable to allocate memory for"
@@ -6795,10 +6807,18 @@ next:
return 0;
}

- sg_init_table(&task->task_sg[0], task->task_sg_num);
+ sg_init_table(&task->task_sg[0], task_sg_num_padded);
+ /*
+ * For the chaining case, setup the proper end of SGL for the
+ * initial submission struct task into struct se_subsystem_api.
+ * This will be cleared later by transport_do_task_sg_chain()
+ */
+ if (task->task_padded_sg)
+ sg_mark_end(&task->task_sg[task->task_sg_num - 1]);

- DEBUG_SC("Successfully allocated task->task_sg_num(%u)\n",
- task->task_sg_num);
+ DEBUG_SC("Successfully allocated task->task_sg_num(%u),"
+ " task_sg_num_padded(%u)\n", task->task_sg_num,
+ task_sg_num_padded);

return task->task_sg_num;
}
@@ -7021,6 +7041,103 @@ next:
return 0;
}

+/*
+ * 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_head = NULL, *sg_link = NULL, *sg_first = NULL;
+ struct scatterlist *sg_head_cur = NULL, *sg_link_cur = NULL;
+ struct scatterlist *sg, *sg_end = NULL, *sg_end_cur = NULL;
+ struct se_task *task;
+ struct target_core_fabric_ops *tfo = CMD_TFO(cmd);
+ u32 task_sg_num = 0, sg_count = 0;
+ int i;
+
+ if (tfo->task_sg_chaining == 0) {
+ printk(KERN_ERR "task_sg_chaining is diabled for fabric module:"
+ " %s\n", tfo->get_fabric_name());
+ dump_stack();
+ return;
+ }
+ /*
+ * Walk the struct se_task list and setup scatterlist chains
+ * for each contiguosly allocated struct se_task->task_sg[].
+ */
+ list_for_each_entry(task, &T_TASK(cmd)->t_task_list, t_list) {
+ if (!(task->task_sg) || !(task->task_padded_sg))
+ continue;
+
+ if (sg_head && sg_link) {
+ sg_head_cur = &task->task_sg[0];
+ sg_link_cur = &task->task_sg[task->task_sg_num];
+ /*
+ * Either add chain or mark end of scatterlist
+ */
+ if (!(list_is_last(&task->t_list,
+ &T_TASK(cmd)->t_task_list))) {
+ /*
+ * Clear existing SGL termination bit set in
+ * transport_calc_sg_num(), see sg_mark_end()
+ */
+ sg_end_cur = &task->task_sg[task->task_sg_num - 1];
+ sg_end_cur->page_link &= ~0x02;
+
+ sg_chain(sg_head, task_sg_num, sg_head_cur);
+ sg_count += (task->task_sg_num + 1);
+ } else
+ sg_count += task->task_sg_num;
+
+ sg_head = sg_head_cur;
+ sg_link = sg_link_cur;
+ task_sg_num = task->task_sg_num;
+ continue;
+ }
+ sg_head = sg_first = &task->task_sg[0];
+ sg_link = &task->task_sg[task->task_sg_num];
+ task_sg_num = task->task_sg_num;
+ /*
+ * Check for single task..
+ */
+ if (!(list_is_last(&task->t_list, &T_TASK(cmd)->t_task_list))) {
+ /*
+ * Clear existing SGL termination bit set in
+ * transport_calc_sg_num(), see sg_mark_end()
+ */
+ sg_end = &task->task_sg[task->task_sg_num - 1];
+ sg_end->page_link &= ~0x02;
+ sg_count += (task->task_sg_num + 1);
+ } else
+ sg_count += task->task_sg_num;
+ }
+ /*
+ * Setup the starting pointer and total t_tasks_sg_linked_no including
+ * padding SGs for linking and to mark the end.
+ */
+ T_TASK(cmd)->t_tasks_sg_chained = sg_first;
+ T_TASK(cmd)->t_tasks_sg_chained_no = sg_count;
+
+ printk("Setup T_TASK(cmd)->t_tasks_sg_chained: %p and"
+ " t_tasks_sg_chained_no: %u\n", T_TASK(cmd)->t_tasks_sg_chained,
+ T_TASK(cmd)->t_tasks_sg_chained_no);
+
+ for_each_sg(T_TASK(cmd)->t_tasks_sg_chained, sg,
+ T_TASK(cmd)->t_tasks_sg_chained_no, i) {
+
+ printk("SG: %p page: %p length: %d offset: %d\n",
+ sg, sg_page(sg), sg->length, sg->offset);
+ if (sg_is_chain(sg))
+ printk("SG: %p sg_is_chain=1\n", sg);
+ if (sg_is_last(sg))
+ printk("SG: %p sg_is_last=1\n", sg);
+ }
+
+}
+EXPORT_SYMBOL(transport_do_task_sg_chain);
+
static int transport_do_se_mem_map(
struct se_device *dev,
struct se_task *task,
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 0833612..dbcc04a 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -439,6 +439,7 @@ struct se_transport_task {
u32 t_tasks_no;
u32 t_tasks_sectors;
u32 t_tasks_se_num;
+ u32 t_tasks_sg_chained_no;
atomic_t t_fe_count;
atomic_t t_se_count;
atomic_t t_task_cdbs_left;
@@ -462,6 +463,8 @@ struct se_transport_task {
struct completion t_transport_passthrough_wcomp;
struct completion transport_lun_fe_stop_comp;
struct completion transport_lun_stop_comp;
+ struct scatterlist *t_tasks_sg_chained;
+ struct scatterlist t_tasks_sg_bounce;
void *t_task_buf;
void *t_task_pt_buf;
struct list_head t_task_list;
@@ -476,6 +479,7 @@ struct se_task {
u8 task_flags;
int task_error_status;
int task_state_flags;
+ int task_padded_sg:1;
unsigned long long task_lba;
u32 task_no;
u32 task_sectors;
diff --git a/include/target/target_core_fabric_ops.h b/include/target/target_core_fabric_ops.h
index e620eda..5dd61a9 100644
--- a/include/target/target_core_fabric_ops.h
+++ b/include/target/target_core_fabric_ops.h
@@ -3,6 +3,12 @@ struct target_fabric_configfs;

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
+ */
+ int task_sg_chaining:1;
char *(*get_fabric_name)(void);
u8 (*get_fabric_proto_ident)(struct se_portal_group *);
char *(*tpg_get_wwn)(struct se_portal_group *);
diff --git a/include/target/target_core_transport.h b/include/target/target_core_transport.h
index 711ec71..2eee898 100644
--- a/include/target/target_core_transport.h
+++ b/include/target/target_core_transport.h
@@ -263,6 +263,7 @@ extern int transport_map_sg_to_mem(struct se_cmd *, struct list_head *,
extern int transport_map_mem_to_sg(struct se_task *, struct list_head *,
void *, struct se_mem *,
struct se_mem **, u32 *, u32 *);
+extern void transport_do_task_sg_chain(struct se_cmd *);
extern u32 transport_generic_get_cdb_count(struct se_cmd *,
struct se_transform_info *,
unsigned long long, u32, struct se_mem *,
--
1.5.6.5


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