passt/tap.c, branch 2026_05_26.038c51e

conf, repair, tap: Document reasons for blocking Unix sockets

2026-05-19T23:23:47+00:00

Most of our operation is asynchronous, based on non-blocking fds handled
in our epoll loop.  However, our several Unix sockets (tap client, repair
helper, control client) are all blocking fds after accept().

That is in fact correct, but for not especially obvious reasons that are
slightly different in each case.  Add explanatory comments to each of them.

Signed-off-by: David Gibson 
[sbrivio: Fixed minor coding style detail in comment in conf_accept()]
Signed-off-by: Stefano Brivio

tap: Report accept() errors

2026-05-19T23:22:22+00:00

Currently, if accept4() fails in tap_listen_handler(), we carry on as if
it succeeded.  Something will probably fail shortly down the line, but
that's needlessly confusing.  Report an error instead.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

treewide: Add SOCK_CLOEXEC to accept() calls that are missing it

2026-05-19T23:22:17+00:00

Generally we try to set the O_CLOEXEC flag on every fd we create.  This
seems to be generally accepted security best practice these days, and we
never exec(), so certainly have no need to pass fds to exec()ed processes.

A handful of accept4() calls on Unix sockets are missing the SOCK_CLOEXEC
flag to set this though.  Add the missing flag.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

pcap: Pass explicit L2 length to pcap_iov()

2026-05-19T23:21:42+00:00

With vhost-user multibuffer frames, the iov can be larger than the
actual L2 frame. The previous approach of computing L2 length as
iov_size() - offset would overcount and write extra bytes into the
pcap file.

Pass the L2 frame length explicitly to pcap_frame() and pcap_iov(),
and write exactly that many bytes instead of the full iov remainder.

Signed-off-by: Laurent Vivier 
Reviewed-by: Jon Maloy 
Reviewed-by: David Gibson 
Signed-off-by: Stefano Brivio

checksum: Pass explicit L4 length to checksum functions

2026-05-19T23:21:38+00:00

The iov_tail passed to csum_iov_tail() may contain padding or trailing
data beyond the actual L4 payload.  Rather than relying on
iov_tail_size() to determine how many bytes to checksum, pass the
length explicitly so that only the relevant payload bytes are included
in the checksum computation.

Signed-off-by: Laurent Vivier 
Reviewed-by: David Gibson 
Reviewed-by: Jon Maloy 
Signed-off-by: Stefano Brivio

ip: Prepare ip.[ch] for sharing with pesto tool

2026-05-07T06:06:30+00:00

Most things in ip.[ch] related purely to IP addresses and headers with
no dependency on other passt/pasta internals.  A number of these will be
useful to re-use in pesto.  The exception is ipv6_l4hdr() which uses
iov_tail.

The only caller of this is in tap.c, so move the function there.  Along
with moving the constant byteswapping functions to common.h, that lets
ip.[ch] to be linked into pesto as well as passt/pasta.

Signed-off-by: David Gibson 
Reviewed-by: Laurent Vivier 
[sbrivio: Dropped duplicate definition of __bswap_constant_32() while
 at it, reported by Laurent]
Signed-off-by: Stefano Brivio

pesto, log: Share log.h (but not log.c) with pesto tool

2026-05-07T06:06:30+00:00

In pesto we're going to want several levels of error/warning messages, much
like passt itself.  Particularly as we start to share mode code between
passt and pesto, we want to use a similar interface to emit those.  However
we don't want to use the same implementation - logging to a file or syslog
doesn't make sense for the command line tool.

To accomplish this loosely share log.h, but not log.c between pesto and
passt.  In fact, an #ifdef means even most of log.h isn't actually shared,
but we do provide similar warn(), die() etc. macros.

This includes the *_perror() variants, which need strerror().  However,
we want to avoid allocations for pesto as we do for passt, and strerror()
allocates in some libc versions.  Therefore, also move our workaround for
this to be shared with pesto.

Reviewed-by: Laurent Vivier 
[dwg: Based on changes part of a larger patch by Stefano]
Signed-off-by: David Gibson 
[sbrivio: Dropped debug_perror_() as it's not used anyway, Laurent was
 asking about its name]
[sbrivio: Fix conflicts in the Makefile caused by the fact that I'm
 not merging a previous series reworking it]
[sbrivio: For some reason, this triggers some unrelated, but valid,
 cppcheck warnings in tap.c and conf.c: fix / suppress them]
Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson

tap, tcp, udp: Use rate-limited logging

2026-04-15T18:59:35+00:00

Now that rate-limited logging macros are available, promote several
debug messages to higher severity levels.  These messages were
previously kept at debug to prevent guests from flooding host
logs, but with rate limiting they can safely be made visible in
normal operation.

In tap.c, refactor tap4_is_fragment() to use warn_ratelimit() instead
of its ad-hoc rate limiting, and promote the guest MAC address change
message to info level.

In tcp.c, promote the invalid TCP SYN endpoint message to warn level.

In udp.c, promote dropped datagram messages to warn level, and
rate-limit the unrecoverable socket error message.

In udp_flow.c, promote flow allocation failures to err_ratelimit.

Link: https://bugs.passt.top/show_bug.cgi?id=134
Signed-off-by: Anshu Kumari 
Reviewed-by: David Gibson 
Signed-off-by: Stefano Brivio

treewide: Spell ASSERT() as assert()

2026-03-20T20:05:29+00:00

The standard library assert(3), at least with glibc, hits our seccomp
filter and dies with SIGSYS before it's able to print a message, making it
near useless.  Therefore, since 7a8ed9459dfe ("Make assertions actually
useful") we've instead used our own implementation, named ASSERT().

This makes our code look slightly odd though - ASSERT() has the same
overall effect as assert(), it's just a different implementation.  More
importantly this makes it awkward to share code between passt/pasta proper
and things that compile in a more typical environment.  We're going to want
that for our upcoming dynamic configuration tool.

Address this by overriding the standard library's assert() implementation
with our own, instead of giving ours its own name.

The standard assert() is supposed to be omitted if NDEBUG is defined,
which ours doesn't do.  Implement that as well, so ours doesn't
unexpectedly differ.  For the -DNDEBUG case we do this by *not* overriding
assert(), since it will be a no-op anyway.  This requires a few places to
add a #include  to let us compile (albeit with warnings) when
-DNDEBUG.

Signed-off-by: David Gibson 
[sbrivio: Fix some conflicts and missing conversions as a result of
 applying "vu_common: Move iovec management into vu_collect()" first]
Signed-off-by: Stefano Brivio

conf, pasta: Add --splice-only option

2026-01-19T08:12:27+00:00

This patch introduces a mode where we only forward loopback connections
and traffic between two namespaces (via the loopback interface, 'lo'),
without a tap device.

It might be used to fix up podman IPv4 / IPv6 loopback mapping when using
rootlesskit for forwarding ports, or a way to implement isolated containers.

In this mode, --host-lo-to-ns-lo and --no-icmp are automatically enabled.
Option --no-splice is rejected.

Link: https://bugs.passt.top/show_bug.cgi?id=149
Signed-off-by: Yumei Huang 
Signed-off-by: Stefano Brivio