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(a)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 */
--
2.45.2