iov: Introduce iov_memset()

Add a helper to set a range of bytes across an IO vector to a given
value, similar to memset() but operating over scatter-gather buffers.
It skips to the given offset and fills across iovec entries up to the
requested length.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 29 insertions, 0 deletions

diff --git a/iov.c b/iov.c
index ae07439..0188acd 100644
--- a/iov.c
+++ b/iov.c
@@ -171,6 +171,33 @@ size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size)
 }
 
 /**
+ * iov_memset() - Set bytes of an IO vector to a given value
+ * @iov:	IO vector
+ * @iov_cnt:	Number of elements in @iov
+ * @offset:	Byte offset in the iovec at which to start
+ * @c:		Byte value to fill with
+ * @length:	Number of bytes to set
+ * 		Will write less than @length bytes if it runs out of space in
+ * 		the iov
+ */
+/* cppcheck-suppress unusedFunction */
+void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c,
+		size_t length)
+{
+	size_t i;
+
+	i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
+
+	for ( ; i < iov_cnt && length; i++) {
+		size_t n = MIN(iov[i].iov_len - offset, length);
+
+		memset((char *)iov[i].iov_base + offset, c, n);
+		offset = 0;
+		length -= n;
+	}
+}
+
+/**
  * iov_tail_prune() - Remove any unneeded buffers from an IOV tail
  * @tail:	IO vector tail (modified)
  *
diff --git a/iov.h b/iov.h
index b4e50b0..d295d05 100644
--- a/iov.h
+++ b/iov.h
@@ -30,6 +30,8 @@ size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
 		  size_t offset, void *buf, size_t bytes);
 size_t iov_size(const struct iovec *iov, size_t iov_cnt);
 size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size);
+void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c,
+		size_t length);
 
 /*
  * DOC: Theory of Operation, struct iov_tail