On Fri, Mar 06, 2026 at 12:51:19PM +0100, Laurent Vivier wrote:
Add a generic iov_truncate() function that truncates an IO vector to a given number of bytes, returning the number of iov entries that contain data after truncation.
Use it in udp_vu_sock_recv() and tcp_vu_sock_recv() to replace the open-coded truncation logic that adjusted iov entries after recvmsg(). Also convert the direct iov_len assignment in tcp_vu_send_flag() to use iov_truncate() for consistency.
Add an ASSERT() in tcp_vu_data_from_sock() to quiet the Coverity error:
passt/tcp_vu.c:457:3: 19. overflow_const: Expression "dlen + hdrlen", where "dlen" is known to be equal to -86, and "hdrlen" is known to be equal to 86, underflows the type of "dlen + hdrlen", which is type "unsigned long".
Signed-off-by: Laurent Vivier
Reviewed-by: David Gibson
---
Notes: v4: add ASSERT() to quiet the Coverity error v3: use in tcp_vu_send_flag() too v2: use iov_truncate() in udp_vu_sock_recv() too
iov.c | 22 ++++++++++++++++++++++ iov.h | 1 + tcp_vu.c | 20 ++++++++------------ udp_vu.c | 12 +++--------- 4 files changed, 34 insertions(+), 21 deletions(-)
diff --git a/iov.c b/iov.c index ad726daa4cd8..31a3f5bc29e5 100644 --- a/iov.c +++ b/iov.c @@ -147,6 +147,28 @@ size_t iov_size(const struct iovec *iov, size_t iov_cnt) return len; }
+/** + * iov_truncate() - Truncate an IO vector to a given number of bytes + * @iov: IO vector (modified) + * @iov_cnt: Number of entries in @iov + * @size: Total number of bytes to keep + * + * Return: number of iov entries that contain data after truncation + */ +size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size) +{ + size_t i, offset; + + i = iov_skip_bytes(iov, iov_cnt, size, &offset); + + if (i < iov_cnt) { + iov[i].iov_len = offset; + i += !!offset; + } + + return i; +} + /** * iov_tail_prune() - Remove any unneeded buffers from an IOV tail * @tail: IO vector tail (modified) diff --git a/iov.h b/iov.h index d1ab91a94e22..b4e50b0fca5a 100644 --- a/iov.h +++ b/iov.h @@ -29,6 +29,7 @@ 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_truncate(struct iovec *iov, size_t iov_cnt, size_t size);
/* * DOC: Theory of Operation, struct iov_tail diff --git a/tcp_vu.c b/tcp_vu.c index 88be232dca66..fd734e857b3b 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -131,7 +131,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) return ret; }
- flags_elem[0].in_sg[0].iov_len = hdrlen + optlen; + iov_truncate(&flags_iov[0], 1, hdrlen + optlen); payload = IOV_TAIL(flags_elem[0].in_sg, 1, hdrlen);
if (flags & KEEPALIVE) @@ -192,9 +192,9 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, struct msghdr mh_sock = { 0 }; uint16_t mss = MSS_GET(conn); int s = conn->sock; - ssize_t ret, len; size_t hdrlen; int elem_cnt; + ssize_t ret; int i;
*iov_cnt = 0; @@ -247,15 +247,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, ret -= already_sent;
/* adjust iov number and length of the last iov */ - len = ret; - for (i = 0; len && i < elem_cnt; i++) { - struct iovec *iov = &elem[i].in_sg[0]; - - if (iov->iov_len > (size_t)len) - iov->iov_len = len; - - len -= iov->iov_len; - } + i = iov_truncate(&iov_vu[DISCARD_IOV_NUM], elem_cnt, ret);
/* adjust head count */ while (*head_cnt > 0 && head[*head_cnt - 1] >= i) @@ -448,10 +440,14 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) for (i = 0, previous_dlen = -1, check = NULL; i < head_cnt; i++) { struct iovec *iov = &elem[head[i]].in_sg[0]; int buf_cnt = head[i + 1] - head[i]; - ssize_t dlen = iov_size(iov, buf_cnt) - hdrlen; + size_t frame_size = iov_size(iov, buf_cnt); bool push = i == head_cnt - 1; + ssize_t dlen; size_t l2len;
+ ASSERT(frame_size >= hdrlen); + + dlen = frame_size - hdrlen; vu_set_vnethdr(iov->iov_base, buf_cnt);
/* The IPv4 header checksum varies only with dlen */ diff --git a/udp_vu.c b/udp_vu.c index 3520f89e5671..5effca777e0a 100644 --- a/udp_vu.c +++ b/udp_vu.c @@ -71,9 +71,9 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, bool v6, ssize_t *dlen) { const struct vu_dev *vdev = c->vdev; - int iov_cnt, idx, iov_used; - size_t off, hdrlen, l2len; struct msghdr msg = { 0 }; + int iov_cnt, iov_used; + size_t hdrlen, l2len;
ASSERT(!c->no_udp);
@@ -115,13 +115,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, iov_vu[0].iov_base = (char *)iov_vu[0].iov_base - hdrlen; iov_vu[0].iov_len += hdrlen;
- /* count the numbers of buffer filled by recvmsg() */ - idx = iov_skip_bytes(iov_vu, iov_cnt, *dlen + hdrlen, &off); - - /* adjust last iov length */ - if (idx < iov_cnt) - iov_vu[idx].iov_len = off; - iov_used = idx + !!off; + iov_used = iov_truncate(iov_vu, iov_cnt, *dlen + hdrlen);
/* pad frame to 60 bytes: first buffer is at least ETH_ZLEN long */ l2len = *dlen + hdrlen - VNET_HLEN; -- 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