[lxc-devel] lxc_container->start fork keeping server sockets alive?

[John Keiser]

Ah!  Should it?  Like, should it do all the daemon things that the
container itself does?


On Thu, Mar 27, 2014 at 12:30 PM, Serge Hallyn <serge.hallyn at ubuntu.com>wrote:

> Quoting John Keiser (jkeiser at getchef.com):
> > Hi all,
> >
> > I am trying to use lxc_container->start() from within a process that
> > happens to have started a TCP server, and even when my program exits, the
> > server socket stays alive.  This can be tested by running this program
> > (which starts a server and then starts a container) twice--the second
> time
> > resulting in a bind() error:
> >
> > #include <sys/socket.h>
> > #include <netinet/in.h>
> > #include <stdio.h>
> > #include <errno.h>
> > #include <strings.h>
> > #include <stdlib.h>
> > #include <lxc/lxccontainer.h>
> >
> > int main(int argc, char**argv)
> > {
> >   struct lxc_container *c;
> >   int listenfd,connfd,n;
> >   struct sockaddr_in servaddr;
> >   int port;
> >
> >   // Start server
> >   port = atoi(argv[2]);
> >   printf("Listening on port %d ...\n", port);
> >   listenfd=socket(AF_INET,SOCK_STREAM,0);
> >   bzero(&servaddr,sizeof(servaddr));
> >   servaddr.sin_family = AF_INET;
> >   servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
> >   servaddr.sin_port=htons(port);
> >   if (bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr)))
> >   {
> >     perror("Error calling bind()");
> >     exit(1);
> >   }
> >   listen(listenfd,1024);
> >
> >   // Start
> >   printf("Starting container ...\n");
> >   c = lxc_container_new(argv[1], NULL);
> >   c->want_daemonize(c, true);
> >   c->want_close_all_fds(c, true);
> >   c->start(c, 0, NULL);
> >
> >   return 0;
> > }
> >
> >
> > *> gcc test.c -llxc -o test*
> > *> lxc-create -n blarghle -t ubuntu*
> >
> > *> ./test blarghle 9050*
> > Listening on port 9050 ...
> > Starting container ...
> > *> ./test blarghle 9050*
> > Listening on port 9050 ...
> > Error calling bind(): Address already in use
> >
> > As you can see, even though ./test finished the first time, the second
> > ./test cannot bind to the port because it is still in use.
> >
> > This appears to be because the lxc init process has a ghost "./test" as
> its
> > parent:
> >
> > *> ps -ef | grep 30276*
> > root     30276     1  0 18:37 ?        00:00:00 ./test blarghle 9050
> > root     30285 30276  0 18:37 ?        00:00:00 /sbin/init
> > *> lsof | grep 9050*
> > test      30276              root    3u     IPv4             366649
> >  0t0        TCP *:9050 (LISTEN)
>
> Hm.  That's the container monitor.  It doesn't close all fds like
> container init does.
>
> > I am stymied on how to investigate further.  My best guess is it has to
> do
> > with the double forking in
> > lxccontainer.h<
> https://github.com/lxc/lxc/blob/master/src/lxc/lxccontainer.c#L608-L621>,
> > though I don't really understand what that is for yet :)  Any thoughts?
> >
> > Thanks!
> >
> > --John
>
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
>
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