[PATCH v8 2/3] iov: Introduce IOV_PUSH_HEADER() macro

Laurent Vivier
2026-04-16T16:09:34Z

Add iov_push_header_() and its typed wrapper IOV_PUSH_HEADER() to write
a header into an iov_tail at the current offset and advance past it.

This is the write counterpart to IOV_PEEK_HEADER() / IOV_REMOVE_HEADER(),
using iov_from_buf() to copy the header data across iovec boundaries.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
iov.c | 23 +++++++++++++++++++++++
iov.h | 11 +++++++++++
2 files changed, 34 insertions(+)

diff --git a/iov.c b/iov.c
index 28c6d40d2986..b1bcdc4649df 100644
--- a/iov.c
+++ b/iov.c
@@ -360,6 +360,29 @@ void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align)
return v;
}

+/**
+ * iov_push_header_() - Write a new header 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_push_header_(struct iov_tail *tail, const void *v, size_t len)
+{
+ size_t l;
+
+ if (!iov_tail_prune(tail))
+ return 0; /* No space */
+
+ l = iov_from_buf(tail->iov, tail->cnt, tail->off, v, len);
+
+ tail->off = 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 3c63308e554f..4fdf14a85b19 100644
--- a/iov.h
+++ b/iov.h
@@ -93,6 +93,7 @@ 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_push_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);
@@ -115,6 +116,16 @@ ssize_t iov_tail_clone(struct iovec *dst_iov, size_t dst_iov_cnt,
sizeof(var_), \
__alignof__(var_))))

+/**
+ * IOV_PUSH_HEADER() - Write a new header to an IOV tail
+ * @tail_: IOV tail to write header to
+ * @var_: A variable containing the header data to write
+ *
+ * Return: number of bytes written
+ */
+#define IOV_PUSH_HEADER(tail_, var_) \
+ (iov_push_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)
--
2.53.0