[PATCH v2 06/13] iov: Add IOV_PUT_HEADER() to write header data back to iov_tail

[Laurent Vivier <lvivier@redhat.com>]

Add a counterpart to IOV_PEEK_HEADER() that writes header data back
to an iov_tail after modification. If the header pointer matches the
original iov buffer location, it only advances the offset. Otherwise,
it copies the data using iov_from_buf().

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 iov.c | 24 ++++++++++++++++++++++++
 iov.h | 14 +++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/iov.c b/iov.c
index cd48667226f3..296f24b61067 100644
--- a/iov.c
+++ b/iov.c
@@ -305,6 +305,30 @@ void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align)
 	return v;
 }
 
+/**
+ * iov_put_header_() - Write header back to an IOV tail
+ * @tail:	IOV tail to write header to
+ * @v:		Pointer to header data to write
+ * @len:	Length of header to write, in bytes
+ *
+ * Return: number of bytes written
+ */
+/* cppcheck-suppress unusedFunction */
+size_t iov_put_header_(struct iov_tail *tail, const void *v, size_t len)
+{
+	size_t l = len;
+
+	/* iov_peek_header_() already called iov_check_header() */
+	if ((char *)tail->iov[0].iov_base + tail->off != v)
+		l = iov_from_buf(tail->iov, tail->cnt, tail->off, v, len);
+
+	ASSERT(l == len);
+
+	tail->off += l;
+
+	return l;
+}
+
 /**
  * iov_remove_header_() - Remove a header from an IOV tail
  * @tail:	IOV tail to remove header from (modified)
diff --git a/iov.h b/iov.h
index d295d05b3bab..fe7c5163d2ab 100644
--- a/iov.h
+++ b/iov.h
@@ -90,6 +90,7 @@ bool iov_tail_prune(struct iov_tail *tail);
 size_t iov_tail_size(struct iov_tail *tail);
 bool iov_drop_header(struct iov_tail *tail, size_t len);
 void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align);
+size_t iov_put_header_(struct iov_tail *tail, const void *v, size_t len);
 void *iov_remove_header_(struct iov_tail *tail, void *v, size_t len, size_t align);
 ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
 		       struct iov_tail *tail);
@@ -112,6 +113,16 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
 					       sizeof(var_),		\
 					       __alignof__(var_))))
 
+/**
+ * IOV_PUT_HEADER() - Write header back to an IOV tail
+ * @tail_:	IOV tail to write header to
+ * @var_:	Pointer to a variable containing the header data to write
+ *
+ * Return: number of bytes written
+ */
+#define IOV_PUT_HEADER(tail_, var_)					\
+	(iov_put_header_((tail_), (var_), sizeof(*var_)))
+
 /**
  * IOV_REMOVE_HEADER() - Remove and return typed header from an IOV tail
  * @tail_:	IOV tail to remove header from (modified)
@@ -130,7 +141,8 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
 	((__typeof__(var_) *)(iov_remove_header_((tail_), &(var_),	\
 				    sizeof(var_), __alignof__(var_))))
 
-/** IOV_DROP_HEADER() - Remove a typed header from an IOV tail
+/**
+ * IOV_DROP_HEADER() - Remove a typed header from an IOV tail
  * @tail_:	IOV tail to remove header from (modified)
  * @type_:	Data type of the header to remove
  *
-- 
2.53.0