The iov_get_ptr() data returns a pointer to contiguous data within a
vector. This allows the caller to manipulate data inside the vector
without copying in/out using iov_from_buf()/iov_to_buf() when we know
that data is contiguous within an iovec element.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
iov.c | 25 +++++++++++++++++++++++++
iov.h | 11 +++++++++++
2 files changed, 36 insertions(+)
diff --git a/iov.c b/iov.c
index 6eed089..bc78c34 100644
--- a/iov.c
+++ b/iov.c
@@ -395,3 +395,28 @@ size_t iov_discard(struct iovec **iov, unsigned int
*iov_cnt, ssize_t bytes)
}
return total;
}
+
+void *iov_get_ptr(struct iovec *iov, unsigned int iov_cnt,
+ ssize_t offset, size_t bytes)
+{
+ if (offset < 0) {
+ offset += iov_size(iov, iov_cnt);
+ if (offset < 0) {
+ return NULL; /* offset before beginning of vector */
+ }
+ }
+
+ while (iov_cnt > 0) {
+ if (offset < iov->iov_len) {
+ if (bytes > iov->iov_len - offset) {
+ return NULL; /* would span iovec elements */
+ }
+ return iov->iov_base + offset;
+ }
+
+ offset -= iov->iov_len;
+ iov_cnt--;
+ iov++;
+ }
+ return NULL; /* offset beyond end of vector */
+}
diff --git a/iov.h b/iov.h
index d6d1fa6..674dd51 100644
--- a/iov.h
+++ b/iov.h
@@ -108,3 +108,14 @@ unsigned iov_copy(struct iovec *dst_iov, unsigned int
dst_iov_cnt,
* smaller than requested if the vector is too small.
*/
size_t iov_discard(struct iovec **iov, unsigned int *iov_cnt, ssize_t bytes);
+
+/*
+ * Get a pointer into a vector at offset if the given number of bytes is
+ * contiguous and not split across iovec elements. NULL is returned if
+ * memory would span iovec elements or exceed the length of the vector.
+ *
+ * The offset is ssize_t so that an offset from the end of the vector can
+ * be specified with a negative number.
+ */
+void *iov_get_ptr(struct iovec *iov, unsigned int iov_cnt, ssize_t offset,
+ size_t bytes);
--
1.8.0
