[PATCH 4/5] iov: add iov_count()

[Laurent Vivier <lvivier@redhat.com>]

Add a function that count how many buffers from a given
iovec list we need to contain a given number of bytes.
It also provides how many bytes are used in the last
buffer if it is not fully filled.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 iov.c | 35 +++++++++++++++++++++++++++++++++++
 iov.h |  2 ++
 2 files changed, 37 insertions(+)

diff --git a/iov.c b/iov.c
index 3741db21790f..793788b5d2bc 100644
--- a/iov.c
+++ b/iov.c
@@ -155,3 +155,38 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt)
 
 	return len;
 }
+
+/**
+ * iov_count - Calculate the number of I/O vectors and the size of
+ *             the last one to store a given number of bytes.
+ *
+ * @iov:       Pointer to the array of struct iovec describing the
+ *             scatter/gather I/O vector.
+ * @iov_cnt:   Number of elements in the iov array.
+ * @size:      number of bytes we need to store in iovec
+ * @last_iov_length: output parameter, length used in the last iovec
+ * 		if return value is 0, this output parameter is
+ * 		undefined.
+ *
+ * Returns:	The number of iovec needed to store @size bytes.
+ */
+/* cppcheck-suppress unusedFunction */
+size_t iov_count(const struct iovec *iov, size_t iov_cnt,
+                 size_t size, size_t *last_iov_length)
+{
+	size_t n = 0;
+
+	while (size && n < iov_cnt) {
+		if (size <= iov[n].iov_len) {
+			*last_iov_length = size;
+			return n + 1;
+		}
+		size -= iov[n].iov_len;
+		n++;
+	}
+
+	if (n > 0)
+		*last_iov_length = iov[n - 1].iov_len;
+
+	return n;
+}
diff --git a/iov.h b/iov.h
index a9e1722713b3..0fa456d7051b 100644
--- a/iov.h
+++ b/iov.h
@@ -28,4 +28,6 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
 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_count(const struct iovec *iov, size_t iov_cnt,
+		 size_t size, size_t *last_iov_length);
 #endif /* IOVEC_H */
-- 
@@ -28,4 +28,6 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
 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_count(const struct iovec *iov, size_t iov_cnt,
+		 size_t size, size_t *last_iov_length);
 #endif /* IOVEC_H */
-- 
2.45.2