`socket-fd` rejects `AF_UNIX` sockets

[h7x4]

Search before asking

• I had searched in the issues and found no similar issues.

Version

OS is NixOS from a nixpkgs instance checked out at a9e7b5456522e9ee5857bb9812f27864d8e80f8a
Kvrocks: 2.16.0

Minimal reproduce step

Configure kvrocks with config:

daemonize no
dir /var/lib/kvrocks
socket-fd 3
supervised systemd
unixsocket /run/kvrocks/kvrocks.sock

And socket activate with systemd socket unit:

[Socket]
Accept=false
SocketGroup=kvrocks
SocketUser=kvrocks
ListenStream=/run/kvrocks/kvrocks.sock

[Install]
WantedBy=sockets.target

Systemd service:

[Unit]
After=network.target kvrocks.socket
Requires=kvrocks.socket

[Service]
Type=notify
User=kvrocks
Group=kvrocks
ExecStart=/usr/bin/kvrocks -c /etc/kvrocks/kvrocks.conf

[Install]
WantedBy=multi-user.target

What did you expect to see?

I expected kvrocks to pick up the unix socket provided on fd 3 and use it to listen for connections.

What did you see instead?

From journal:

systemd[1]: Starting Kvrocks - Distributed key value database...
kvrocks[1714]: [2026-08-11T15:45:19.154330+00:00][I][main.cc:171] kvrocks version 2.16.0
systemd[1]: Started Kvrocks - Distributed key value database.
kvrocks[1714]: [2026-08-11T15:45:19.214740+00:00][I][storage.cc:410] [storage] Success to load the data from disk: 49 ms
kvrocks[1714]: [2026-08-11T15:45:19.221324+00:00][E][worker.cc:66] [worker] Failed to listen to socket with fd: 3, Error: The port of the provided socket fd doesn't match the configured port
systemd[1]: kvrocks.service: Main process exited, code=exited, status=1/FAILURE
systemd[1]: kvrocks.service: Failed with result 'exit-code'.

Anything Else?

Error triggered here:

kvrocks/src/server/worker.cc

Lines 232 to 236 in 3c1ac18

	Status Worker::listenFD(int fd, uint32_t expected_port, int backlog) {
	const uint32_t port = util::GetLocalPort(fd);
	if (port != expected_port) {
	return {Status::NotOK, "The port of the provided socket fd doesn't match the configured port"};
	}

Implementation of util::GetLocalPort for context:

kvrocks/src/common/io_util.cc

Lines 350 to 364 in 3c1ac18

	int GetLocalPort(int fd) {
	sockaddr_in6 address;
	socklen_t len = sizeof(address);
	if (getsockname(fd, (sockaddr *)&address, &len) == -1) {
	return 0;
	}
	if (address.sin6_family == AF_INET) {
	return ntohs(reinterpret_cast<sockaddr_in *>(&address)->sin_port);
	} else if (address.sin6_family == AF_INET6) {
	return ntohs(address.sin6_port);
	}
	return 0;
	}

I'm not entirely sure if the socket-fd field is only intended for workers, but assuming it is not (or maybe even if it is), I don't think it should need to care about whether the port aligns with whatever is set in the config. Whatever provided the file descriptor can be in charge of the chosen port/socket path.

I'd be willing to submit a PR, but I'm not sure what direction you'd like to take this in, so I'll wait for input.

Are you willing to submit a PR?

• I'm willing to submit a PR!

[jihuayu]

wow! Thank you! Nix packages look really cool.

I don't think this is that simple. The socket-fd abstraction would need a fairly significant change. The current abstraction is built around an inherited TCP listening socket, rather than a generic inherited socket. To support AF_UNIX, we'd need to rework the abstraction as a whole.

cc @PragmaTwice @git-hulk. Do you have any thoughts on this?

[h7x4]

Just thought I'd mention another related find, fd-passed sockets seemingly never gets set to nonblocking. For NixOS we set NonBlocking=true in the systemd service, but it might be worthwhile to handle it in the code instead, like how it's being done for Worker::Listen*. Worst case it's gonna be a noop.

[PragmaTwice]

For Unix socket we have special configuration options.

See https://github.com/apache/kvrocks/blob/unstable/kvrocks.conf#L20.

Could this solve your problem?

[h7x4]

No, unfortunately not. These options only affect sockets created from within the program, not fd-passed ones.

[PragmaTwice]

Hmmm I'll try to make some time this weekend to look into this issue.