These utilities enhance iov_tail manipulation, useful for
efficient packet processing by enabling iovec array cloning and
header stripping without data copies.
- iov_drop_header(): Discards a specified number of bytes from the
beginning of an iov_tail by advancing its internal offset and pruning
consumed elements.
- iov_tail_clone(): Clone an iov_tail into an iovec array, adjusting the
first iovec entry to remove the iov_tail offset.
Signed-off-by: Laurent Vivier
Reviewed-by: David Gibson
---
iov.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
iov.h | 3 +++
2 files changed, 54 insertions(+)
diff --git a/iov.c b/iov.c
index edf0444d1955..9a91eb63026a 100644
--- a/iov.c
+++ b/iov.c
@@ -192,6 +192,21 @@ size_t iov_tail_size(struct iov_tail *tail)
return iov_size(tail->iov, tail->cnt) - tail->off;
}
+/**
+ * iov_drop_header() - Discard a header from an IOV tail
+ * @tail: IO vector tail
+ * @len: length to move the head of the tail
+ *
+ * Return: true if the item still contains any bytes, otherwise false
+ */
+/* cppcheck-suppress unusedFunction */
+bool iov_drop_header(struct iov_tail *tail, size_t len)
+{
+ tail->off = tail->off + len;
+
+ return iov_tail_prune(tail);
+}
+
/**
* iov_peek_header_() - Get pointer to a header from an IOV tail
* @tail: IOV tail to get header from
@@ -248,3 +263,39 @@ void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align)
tail->off = tail->off + len;
return p;
}
+
+/**
+ * iov_tail_clone() - Clone an iov tail into a new iovec array
+ *
+ * @dst_iov: Pointer to the destination array of struct iovec describing
+ * the scatter/gather I/O vector to shallow copy to.
+ * @dst_iov_cnt: Maximum number of elements in the destination iov array.
+ * @tail: Pointer to the source iov_tail
+ *
+ * Return: the number of elements successfully referenced from the destination
+ * iov array, a negative value if there is not enough room in the
+ * destination iov array
+ */
+/* cppcheck-suppress unusedFunction */
+ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
+ struct iov_tail *tail)
+{
+ const struct iovec *iov = &tail->iov[0];
+ size_t iov_cnt = tail->cnt;
+ size_t offset = tail->off;
+ unsigned int i, j;
+
+ i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
+
+ /* assign iov references referencing a subset of the source one */
+ for (j = 0; i < iov_cnt && j < dst_iov_cnt; i++, j++) {
+ dst_iov[j].iov_base = (char *)iov[i].iov_base + offset;
+ dst_iov[j].iov_len = iov[i].iov_len - offset;
+ offset = 0;
+ }
+
+ if (j == dst_iov_cnt && i != iov_cnt)
+ return -1;
+
+ return j;
+}
diff --git a/iov.h b/iov.h
index 3fc96ab9755a..c94fabe1eb43 100644
--- a/iov.h
+++ b/iov.h
@@ -72,8 +72,11 @@ struct iov_tail {
bool iov_tail_prune(struct iov_tail *tail);
size_t iov_tail_size(struct iov_tail *tail);
+bool iov_drop_header(struct iov_tail *tail, size_t len);
void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align);
void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align);
+ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
+ struct iov_tail *tail);
/**
* IOV_PEEK_HEADER() - Get typed pointer to a header from an IOV tail
--
2.49.0