From: Xiubo Li <lixi...@cmss.chinamobile.com>
Add some comments to make the scatter code to be more readable.
Signed-off-by: Xiubo Li <lixi...@cmss.chinamobile.com>
---
drivers/target/target_core_user.c | 30 +++++++++++++++++++++++++-----
1 file changed, 25 insertions(+), 5 deletions(-)
diff --git a/drivers/target/target_core_user.c
b/drivers/target/target_core_user.c
index 9030c2a..4f529ed3 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -532,8 +532,7 @@ 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)
+static inline void new_iov(struct iovec **iov, int *iov_cnt)
{
struct iovec *iovec;
@@ -586,19 +585,38 @@ static int scatter_data_area(struct tcmu_dev *udev,
to = kmap_atomic(page);
}
- copy_bytes = min_t(size_t, sg_remaining,
- block_remaining);
+ /*
+ * Covert to virtual offset of the ring data area.
+ */
to_offset = get_block_offset_user(udev, dbi,
block_remaining);
+ /*
+ * The following code will gather and map the blocks
+ * to the same iovec when the blocks are all next to
+ * each other.
+ */
+ copy_bytes = min_t(size_t, sg_remaining,
+ block_remaining);
if (*iov_cnt != 0 &&
to_offset == iov_tail(*iov)) {
+ /*
+ * Will append to the current iovec, because
+ * the current block page is next to the
+ * previous one.
+ */
(*iov)->iov_len += copy_bytes;
} else {
- new_iov(iov, iov_cnt, udev);
+ /*
+ * Will allocate a new iovec because we are
+ * first time here or the current block page
+ * is not next to the previous one.
+ */
+ new_iov(iov, iov_cnt);
(*iov)->iov_base = (void __user *)to_offset;
(*iov)->iov_len = copy_bytes;
}
+
if (copy_data) {
offset = DATA_BLOCK_SIZE - block_remaining;
memcpy(to + offset,
@@ -606,11 +624,13 @@ static int scatter_data_area(struct tcmu_dev *udev,
copy_bytes);
tcmu_flush_dcache_range(to, copy_bytes);
}
+
sg_remaining -= copy_bytes;
block_remaining -= copy_bytes;
}
kunmap_atomic(from - sg->offset);
}
+
if (to)
kunmap_atomic(to);
--
1.8.3.1
