On 12/15/2011 07:53 PM, Michael D. Berger wrote:
[...]
Hmm? You should usually consume all fds you get passed. And
if you cannot handle more than one, then exit quickly with an
error message. And if any of the fds is invalid, then print
an error message and leave, too.
This is what I'd usually use:
int fd, n;
n = sd_listen_fds();
if (n< 0) {
fprintf(stderr, "sd_listen_fds(): %s\n", strerror(-n));
exit(1);
}
for (fd = SD_LISTEN_FDS_START; fd< SD_LISTEN_FDS_START + n; fd ++) {
if (sd_is_socket_inet(fd, ...)<= 0) {
fprintf(stderr, "Invalid socket passed.\n");
exit(1);
}
/* do something with the fd... */ }
(This is for the generic case where the service can handle
more than one fd. If you can handle ony one, then check
whether n == 1 and if it isn't exit saying you can't deal
with more than one fd.)
Lennart
What you say is clear, but I am perplexed by the fact that
in a case where there will be one handle, that handle will
always be 3. How do we know that 3 is not being used by
something else? I thought that the system has to choose
a handle that is available.
Hi,
"the system", i.e. systemd, controls exactly what file descriptors are
passed to the child process. In this case "the system" chooses to always
use 3 for the first socket to pass to the child. It can, because the
sockets are opened before the child is executed and their numbering is
controlled by the parent. So even if the child has a library which opens
a file very early, it will always be later the the time that systemd
picks it file descriptors.
HTH,
Zbyszek
Mike.
--
Michael D. Berger
[email protected]
http://www.rosemike.net/
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