[PATCH v2 4/5] iov: Add iov_memcopy() to copy data between iovec arrays

[Laurent Vivier <lvivier@redhat.com>]

Add a helper to copy data from a source iovec array to a destination
iovec array, each starting at an arbitrary byte offset, iterating
through both arrays simultaneously and copying in chunks matching the
smaller of the two current segments.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 iov.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 iov.h |  2 ++
 2 files changed, 48 insertions(+)

diff --git a/iov.c b/iov.c
index 23cc247fd6f2..5bd8ece5a106 100644
--- a/iov.c
+++ b/iov.c
@@ -196,6 +196,52 @@ void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c,
 	}
 }
 
+/**
+ * iov_memcopy() - Copy data between two iovec arrays
+ * @dst_iov:		Destination iovec array
+ * @dst_iov_cnt:	Number of elements in destination iovec array
+ * @dst_offs:		Destination offset
+ * @iov:		Source iovec array
+ * @iov_cnt:		Number of elements in source iovec array
+ * @offs:		Source offset
+ *
+ * Return: total number of bytes copied
+ */
+/* cppcheck-suppress unusedFunction */
+size_t iov_memcopy(struct iovec *dst_iov, size_t dst_iov_cnt, size_t dst_offs,
+		   const struct iovec *iov, size_t iov_cnt, size_t offs)
+{
+	unsigned int i, j;
+	size_t total = 0;
+
+	i = iov_skip_bytes(iov, iov_cnt, offs, &offs);
+	j = iov_skip_bytes(dst_iov, dst_iov_cnt, dst_offs, &dst_offs);
+
+	/* copying data */
+	while (i < iov_cnt && j < dst_iov_cnt) {
+		size_t len = MIN(dst_iov[j].iov_len - dst_offs,
+				 iov[i].iov_len - offs);
+
+		memcpy((char *)dst_iov[j].iov_base + dst_offs,
+		       (const char *)iov[i].iov_base + offs, len);
+
+		dst_offs += len;
+		offs += len;
+		total += len;
+
+		if (dst_offs == dst_iov[j].iov_len) {
+			dst_offs = 0;
+			j++;
+		}
+		if (offs == iov[i].iov_len) {
+			offs = 0;
+			i++;
+		}
+	}
+
+	return total;
+}
+
 /**
  * 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 7f0eba4ed71c..8439d255caed 100644
--- a/iov.h
+++ b/iov.h
@@ -32,6 +32,8 @@ 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);
+size_t iov_memcopy(struct iovec *dst_iov, size_t dst_iov_cnt, size_t dst_offs,
+		   const struct iovec *iov, size_t iov_cnt, size_t offs);
 
 /*
  * DOC: Theory of Operation, struct iov_tail
-- 
2.53.0