The iov_discard() function removes data from the front or back of the
vector. This is useful when peeling off header/footer structs.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
iov.c | 41 +++++++++++++++++++++++++++++++++++++++++
iov.h | 13 +++++++++++++
2 files changed, 54 insertions(+)
diff --git a/iov.c b/iov.c
index a81eedc..6eed089 100644
--- a/iov.c
+++ b/iov.c
@@ -354,3 +354,44 @@ size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
{
return iov_memset(qiov->iov, qiov->niov, offset, fillc, bytes);
}
+
+size_t iov_discard(struct iovec **iov, unsigned int *iov_cnt, ssize_t bytes)
+{
+ size_t total = 0;
+ struct iovec *cur;
+ int direction;
+
+ if (*iov_cnt == 0) {
+ return 0;
+ }
+
+ if (bytes < 0) {
+ bytes = -bytes;
+ direction = -1;
+ cur = *iov + (*iov_cnt - 1);
+ } else {
+ direction = 1;
+ cur = *iov;
+ }
+
+ while (*iov_cnt > 0) {
+ if (cur->iov_len > bytes) {
+ if (direction > 0) {
+ cur->iov_base += bytes;
+ }
+ cur->iov_len -= bytes;
+ total += bytes;
+ break;
+ }
+
+ bytes -= cur->iov_len;
+ total += cur->iov_len;
+ cur += direction;
+ *iov_cnt -= 1;
+ }
+
+ if (direction > 0) {
+ *iov = cur;
+ }
+ return total;
+}
diff --git a/iov.h b/iov.h
index 34c8ec9..d6d1fa6 100644
--- a/iov.h
+++ b/iov.h
@@ -95,3 +95,16 @@ void iov_hexdump(const struct iovec *iov, const unsigned int
iov_cnt,
unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
const struct iovec *iov, unsigned int iov_cnt,
size_t offset, size_t bytes);
+
+/*
+ * Remove a given number of bytes from the front or back of a vector.
+ * This may update iov and/or iov_cnt to exclude iovec elements that are
+ * no longer required.
+ *
+ * Data is discarded from the front of the vector if bytes is positive and
+ * from the back of the vector if bytes is negative.
+ *
+ * The number of bytes actually discarded is returned. This number may be
+ * smaller than requested if the vector is too small.
+ */
+size_t iov_discard(struct iovec **iov, unsigned int *iov_cnt, ssize_t bytes);
--
1.8.0
