[lxc-devel] lxc_container->start fork keeping server sockets alive?
John Keiser
jkeiser at getchef.com
Thu Mar 27 18:42:45 UTC 2014
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)
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
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