[systemd-devel] Problem with sd_listen_fds(0)

[Donat Zenichev]

Hi systemd community.
Recently I've come accross one interesting problem with API of systemd.
The problem is that, I'm not able to read commands comming to the AF_UNIX
socket, that was created by systemd and passed to my program using
sd_listen_fds(0) function.

What actually program requires, is AF_UNIX (AF_LOCAL) socket of type
SOCK_STREAM.
In case if I create this socket manually, using socket(AF_LOCAL,
SOCK_STREAM, 0) function, it works out as expected.

But, when I create a socket using systemd socket unit, reading fails with
"-1" return value.

What I actually do, is that I check if there are some sockets created for
me using sd_listen_fds(0), and in case it returns 1 (so 1 socket created),
program goes further and sets a file descriptor value to fd =
SD_LISTEN_FDS_START + 0;
Since the SD_LISTEN_FDS_START is pre-defined to value '3', my file
descriptor will always be '3'.

But when it comes to reading, with read() function, it fails with the errno
EINVAL - Invalid argument.
It's not a matter of a other parameters than a file descriptor, since with
manual creation of socket it works out as I said.

An initializing of the socket descriptor, when creating it by systemd
passes as normal, so program starts.
But any further command received on fd fails with '-1' return value.

So my question is, where should I look into?


Socket unit file:
```
[Socket]
ListenStream=/var/run/foobar/foobar.sock
SocketUser=foouser
SocketGroup=foogroup
SocketMode=755

ExecStartPost=-/bin/chown foouser:foogroup /var/run/foobar

[Install]
WantedBy=sockets.target
```

-- 
-- 
BR, Donat Zenichev
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