On Fri, Apr 11, 2025 at 03:10:12PM +0200, Laurent Vivier wrote:iov_tail_drop() discards a header from the iov_tail, iov_slice() makes a new iov referencing a subset of the data in the original iov. Signed-off-by: Laurent Vivier <lvivier(a)redhat.com>Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au> For the actual behaviour, couple of cosmetic nits noted below.--- iov.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ iov.h | 4 ++++ 2 files changed, 72 insertions(+) diff --git a/iov.c b/iov.c index 8c63b7ea6e31..d2aca59e42ed 100644 --- a/iov.c +++ b/iov.c @@ -156,6 +156,59 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt) return len; } +/** + * iov_slice - Make a new iov referencing a subset of the data in the original iov + * + * @dst_iov: Pointer to the destination array of struct iovec describing + * the scatter/gather I/O vector to copy to. + * @dst_iov_cnt: Maximum number of elements in the destination iov array. + * @iov: Pointer to the source array of struct iovec describing + * the scatter/gather I/O vector to copy from. + * @iov_cnt: Maximum number of elements in the source iov array. + * @offset: Offset within the source iov from where copying should start. + * @bytes: On input, total number of bytes to copy from @iov to @dst_iov, + * if @bytes is NULL, copy all the content of @iov, + * on output actual number of bytes copied. + * + * Returns: The number of elements successfully copied to the destination + * iov array, a negative value if there is no enough room in thes/no/not/+ * destination iov array + */ +/* cppcheck-suppress unusedFunction */ +int iov_slice(struct iovec *dst_iov, size_t dst_iov_cnt, + const struct iovec *iov, size_t iov_cnt, + size_t offset, size_t *bytes) +{ + unsigned int i, j; + size_t remaining = bytes ? *bytes : SIZE_MAX; + + i = iov_skip_bytes(iov, iov_cnt, offset, &offset); + + /* copying data */I think this comment is still a bit misleading.+ for (j = 0; i < iov_cnt && j < dst_iov_cnt && remaining; i++) { + size_t len = MIN(remaining, iov[i].iov_len - offset); + + dst_iov[j].iov_base = (char *)iov[i].iov_base + offset; + dst_iov[j].iov_len = len; + j++; + remaining -= len; + offset = 0; + } + if (j == dst_iov_cnt) { + if (bytes) { + if (remaining) + return -1; + } else if (i != iov_cnt) { + return -1; + } + } + + if (bytes) + *bytes -= remaining; + + return j; +} + /** * iov_tail_prune() - Remove any unneeded buffers from an IOV tail * @tail: IO vector tail (modified) @@ -191,6 +244,21 @@ size_t iov_tail_size(struct iov_tail *tail) return iov_size(tail->iov, tail->cnt) - tail->off; } +/** + * iov_tail_drop() - Discard a header from an IOV tail + * @tail: IO vector tail + * @len: length to move the head of the tail + * + * Returns: true if the tail still contains any bytes, otherwise false + */ +/* cppcheck-suppress unusedFunction */ +bool iov_tail_drop(struct iov_tail *tail, size_t len) +{ + tail->off = tail->off + len; + + return iov_tail_prune(tail); +} + /** * iov_peek_header_() - Get pointer to a header from an IOV tail * @tail: IOV tail to get header from diff --git a/iov.h b/iov.h index 9855bf0c0c32..3f8259aa8d28 100644 --- a/iov.h +++ b/iov.h @@ -28,6 +28,9 @@ 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); +int iov_slice(struct iovec *dst_iov, size_t dst_iov_cnt, + const struct iovec *iov, size_t iov_cnt, + size_t offset, size_t *bytes); /* * DOC: Theory of Operation, struct iov_tail @@ -72,6 +75,7 @@ struct iov_tail { bool iov_tail_prune(struct iov_tail *tail); size_t iov_tail_size(struct iov_tail *tail); +bool iov_tail_drop(struct iov_tail *tail, size_t len); void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align); void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align);-- 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