target/user: Use iovec[] to describe continuous area

We don't need use one iovec per scatter-gather list entry, since data
area are continuous.

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

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 94f5154..93de51f 100644 (file)
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -231,6 +231,23 @@ static inline size_t head_to_end(size_t head, size_t size)
        return size - head;
 }
 
+static inline void new_iov(struct iovec **iov, int *iov_cnt,
+                          struct tcmu_dev *udev)
+{
+       struct iovec *iovec;
+
+       if (*iov_cnt != 0)
+               (*iov)++;
+       (*iov_cnt)++;
+
+       iovec = *iov;
+       memset(iovec, 0, sizeof(struct iovec));
+
+       /* Even iov_base is relative to mb_addr */
+       iovec->iov_base = (void __user *) udev->data_off +
+               udev->data_head;
+}
+
 #define UPDATE_HEAD(head, used, size) smp_store_release(&head, ((head % size) + used) % size)
 
 static void alloc_and_scatter_data_area(struct tcmu_dev *udev,
@@ -242,6 +259,10 @@ static void alloc_and_scatter_data_area(struct tcmu_dev *udev,
        size_t copy_bytes;
        struct scatterlist *sg;
 
+       if (data_nents == 0)
+               return;
+
+       new_iov(iov, iov_cnt, udev);
        for_each_sg(data_sg, sg, data_nents, i) {
                copy_bytes = min_t(size_t, sg->length,
                                 head_to_end(udev->data_head, udev->data_size));
@@ -253,12 +274,7 @@ static void alloc_and_scatter_data_area(struct tcmu_dev *udev,
                        tcmu_flush_dcache_range(to, copy_bytes);
                }
 
-               /* Even iov_base is relative to mb_addr */
-               (*iov)->iov_len = copy_bytes;
-               (*iov)->iov_base = (void __user *) udev->data_off +
-                                               udev->data_head;
-               (*iov_cnt)++;
-               (*iov)++;
+               (*iov)->iov_len += copy_bytes;
 
                UPDATE_HEAD(udev->data_head, copy_bytes, udev->data_size);
 
@@ -268,9 +284,8 @@ static void alloc_and_scatter_data_area(struct tcmu_dev *udev,
 
                        copy_bytes = sg->length - copy_bytes;
 
+                       new_iov(iov, iov_cnt, udev);
                        (*iov)->iov_len = copy_bytes;
-                       (*iov)->iov_base = (void __user *) udev->data_off +
-                                                       udev->data_head;
 
                        if (copy_data) {
                                to = (void *) udev->mb_addr +
@@ -279,8 +294,6 @@ static void alloc_and_scatter_data_area(struct tcmu_dev *udev,
                                tcmu_flush_dcache_range(to, copy_bytes);
                        }
 
-                       (*iov_cnt)++;
-                       (*iov)++;
 
                        UPDATE_HEAD(udev->data_head,
                                copy_bytes, udev->data_size);
@@ -393,12 +406,10 @@ static int tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
         * Must be a certain minimum size for response sense info, but
         * also may be larger if the iov array is large.
         *
-        * iovs = sgl_nents+1, for end-of-ring case, plus another 1
-        * b/c size == offsetof one-past-element.
+        * 3 iovs since we can describe the whole continuous are using one
+        * for data, one for bidi and one more in the case of wrap.
        */
-       base_command_size = max(offsetof(struct tcmu_cmd_entry,
-                                        req.iov[se_cmd->t_bidi_data_nents +
-                                                se_cmd->t_data_nents + 2]),
+       base_command_size = max(offsetof(struct tcmu_cmd_entry, req.iov[3]),
                                sizeof(struct tcmu_cmd_entry));
        command_size = base_command_size
                + round_up(scsi_command_size(se_cmd->t_task_cdb), TCMU_OP_ALIGN_SIZE);