On Mon, Mar 09, 2026 at 10:47:37AM +0100, Laurent Vivier wrote:
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
Reviewed-by: David Gibson
--- 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);
This assumes the tail is already pruned. That will be the case assuming this has a matching iov_peek_header_(), but it might be better to explicitly document that assumption. Better yet, is there a way we could enforce these come in pairs. Something like: struct some_header *hdr; with_header(hdr, tail) { hdr->a = 123; hdr->b = hdr->c - 7; } Where, #define with_header(hdr, tail) for ((typeof *(hdr)) store, hdr = IOV_PEEK_HEADER(tail, store); hdr; IOV_PUT_HEADER(tail, hdr), hdr = NULL)
+ 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
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson