compel: Create socket for pid

Compel needs a socket that lives in victim's net namespace.
CRIU creates this socket once for all the processes it works
with. For pure compel case the socket is created for each
new ctl.

travis-ci: success for compel: Contrinue improving library
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

compel/src/lib/infect.c

@@ -959,6 +959,39 @@ out:
 	return ret;
 }
 
+/*
+ * This routine is to create PF_UNIX/SOCK_SEQPACKET socket
+ * in the target net namespace
+ */
+static int make_sock_for(int pid)
+{
+	int ret = -1;
+	int mfd, fd;
+	char p[32];
+
+	sprintf(p, "/proc/%d/ns/net", pid);
+	fd = open(p, O_RDONLY);
+	if (fd < 0)
+		goto out;
+
+	mfd = open("/proc/self/ns/net", O_RDONLY);
+	if (mfd < 0)
+		goto out_c;
+
+	if (setns(fd, CLONE_NEWNET))
+		goto out_cm;
+
+	ret = socket(PF_UNIX, SOCK_SEQPACKET | SOCK_NONBLOCK, 0);
+
+	setns(mfd, CLONE_NEWNET);
+out_cm:
+	close(mfd);
+out_c:
+	close(fd);
+out:
+	return ret;
+}
+
 static int simple_open_proc(int pid, int mode, const char *fmt, ...)
 {
 	int l;
@@ -989,6 +1022,9 @@ struct parasite_ctl *compel_prepare(int pid)
 	ictx->syscall_ip = find_executable_area(pid);
 	if (ictx->syscall_ip == (unsigned long)MAP_FAILED)
 		goto err;
+	ictx->sock = make_sock_for(pid);
+	if (ictx->sock < 0)
+		goto err;
 
 out:
 	return ctl;