passt/tap.c, branch 2026_05_07.1afd4ed

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

treewide: Introduce passt_exit() helper

2025-12-12T21:20:02+00:00

In d0006fa78 ("treewide: use _exit() over exit()"), we replaced use of
the normal exit(3) with direct calls to _exit(2).  That was because glibc
exit(3) made some unexpected futex() calls, which hit our seccomp profile.

We've since had some bugs due to missing the extra cleanup that exit(3)
implemented, for which we've added explicit cleanup calls.  Specifically,
we have fflush() calls in some places to avoid leaving incomplete messages
on stdout/stderr, and in other places fsync_pcap_and_log() to avoid
leaving incomplete log or pcap files.

It's easy to forget these when adding new error paths, so instead,
implement our own passt_exit() wrapper to perform vital cleanup then call
_exit(2).  This also provides an obvious place to add any additional
cleanups we discover we need in future.

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

tap: Pad non-batched frames to 802.3 minimum (60 bytes) if needed

2025-12-08T03:46:55+00:00

IEEE 802.3 requires a minimum frame payload of 46 bytes, without a
802.1Q tag. Add padding for the simple tap_send_single() case using
a zero-filled 60-byte buffer and copying data to it if needed.

In theory, we could add a further element in the iovec array, say:

	uint8_t padding[ETH_ZLEN] = { 0 };
	struct iovec iov[3];

	...

		if (l2len < ETH_ZLEN) {
			iov[iovcnt].iov_base = (void *)padding;
			iov[iovcnt].iov_len = ETH_ZLEN - l2len;
			iovcnt++;
		}

and avoid a copy, but that would substantially complicate the
vhost-user path, and it's questionable whether passing a reference
to a further buffer actually causes lower overhead than the simple
copy.

Link: https://bugs.passt.top/show_bug.cgi?id=166
Signed-off-by: Stefano Brivio 
Reviewed-by: Laurent Vivier

arp/ndp: don't send messages on uninitialized tap interface

2025-11-27T21:29:25+00:00

When running pasta without --config-net, the tap interface is opened
and assigned a valid file descriptor, but intentionally not brought
up in the namespace. This is the expected behavior when the user wants
to configure the namespace manually.

However, in PASTA mode the code is attempting to send ARP announcements
and NDP messages (initial requests and unsolicited NAs) based solely on
whether c->fd_tap is valid, without checking if the interface actually
is up and ready to transmit. This results in send failures, and when
debug is activated (pasta -d) we see error printouts for these early
messages.

We now add new function tap_is_ready() which checks both conditions:
- Whether fd_tap is valid (all modes)
- Whether the tap interface is up (pasta mode only). In this mode, we
  use the existing c->pasta_conf_ns flag, which indicates whether
  pasta_ns_conf() configured and brought up the interface. This test
  is simple, and good enough for now.

We update all functions that send unsolicited ARP/NDP messages to
check with the new function before making any send attempt.

This eliminates spurious send errors when starting pasta without
--config-net, while preserving correct behavior when the interface
is properly initialized.

Signed-off-by: Jon Maloy 
Signed-off-by: Stefano Brivio

epoll_ctl: Extract epoll operations

2025-10-30T14:32:12+00:00

Centralize epoll_add() and epoll_del() helper functions into new
epoll_ctl.c/h files.

This also moves the union epoll_ref definition from passt.h to
epoll_ctl.h where it's more logically placed.

The new epoll_add() helper simplifies adding file descriptors to epoll
by taking an epoll_ref and events, handling error reporting
consistently across all call sites.

Signed-off-by: Laurent Vivier 
[sbrivio: Include epoll_ctl.h from netlink.c as it's now needed there]
Reviewed-by: David Gibson 
Signed-off-by: Stefano Brivio

util: Simplify epoll_del() interface to take epollfd directly

2025-10-30T14:32:03+00:00

Change epoll_del() to accept the epoll file descriptor directly instead
of the full context structure. This simplifies the interface and aligns
with the threading refactoring by reducing dependency on the context
structure for basic epoll operations as we will manage an epollfd per
thread.

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