iov: add iov_discard_front/back() to remove data

The iov_discard_front/back() functions remove data from the front or
back of the vector.  This is useful when peeling off header/footer
structs.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/qemu/iov.h b/include/qemu/iov.h
index d06f8b9..68d25f2 100644
--- a/include/qemu/iov.h
+++ b/include/qemu/iov.h
@@ -99,4 +99,17 @@ 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.
+ *
+ * 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_front(struct iovec **iov, unsigned int *iov_cnt,
+                         size_t bytes);
+size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
+                        size_t bytes);
+
 #endif