From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Brivio To: passt-dev@passt.top Subject: Re: [PATCH 1/2] udp: Don't drop zero-length outbound UDP packets Date: Fri, 09 Sep 2022 11:26:58 +0200 Message-ID: <20220909112658.5dccf03a@elisabeth> In-Reply-To: <20220909042714.762832-2-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0651743195434457026==" --===============0651743195434457026== Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Fri, 9 Sep 2022 14:27:13 +1000 David Gibson wrote: > udp_tap_handler() currently skips outbound packets if they have a payload > length of zero. This is not correct, since in a datagram protocol zero > length packets still have meaning. Right, nice catch. As far as I can tell it's an issue I added with commit bb708111833e ("treewide: Packet abstraction with mandatory boundary checks"). > Adjust this to correctly forward the zero-length packets by using a msghdr > with msg_iovlen =3D=3D 0. >=20 > Bugzilla: https://bugs.passt.top/show_bug.cgi?id=3D19 >=20 > Signed-off-by: David Gibson > --- > udp.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) >=20 > diff --git a/udp.c b/udp.c > index c4ebecc..caa852a 100644 > --- a/udp.c > +++ b/udp.c > @@ -1075,19 +1075,19 @@ int udp_tap_handler(struct ctx *c, int af, const vo= id *addr, > uh_send =3D packet_get(p, i, 0, sizeof(*uh), &len); > if (!uh_send) > return p->count; > + > + mm[i].msg_hdr.msg_name =3D sa; > + mm[i].msg_hdr.msg_namelen =3D sl; > + count++; > + > if (!len) > continue; > =20 > m[i].iov_base =3D (char *)(uh_send + 1); > m[i].iov_len =3D len; I haven't tested this yet, but: - shouldn't iov_len be set to 0 (moving also this line before)? Note that I'm not initialising m - shouldn't iov_base point to NULL to avoid noise from valgrind? Also: > =20 > - mm[i].msg_hdr.msg_name =3D sa; > - mm[i].msg_hdr.msg_namelen =3D sl; > - > mm[i].msg_hdr.msg_iov =3D m + i; > mm[i].msg_hdr.msg_iovlen =3D 1; ...I guess we should still go through those even if the size is zero, because we're appending a message. If we don't, I would expect some subsequent messages in the batch to be dropped (as many as zero sized packets we have). That is, I suppose we could just drop the continue statement on if (!len) above -- but, again, I haven't tested it. --=20 Stefano --===============0651743195434457026==--