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mnexec: mount sysfs in each container

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The sysfs filesystem is [tagged][1] with a set of namespaces when mounted, taken
from the mounting process. Among other things, this controls which network
devices will show up in /sys/class/net and /sys/class/net/bonding_masters.

Without this change, mininet will not mount sysfs in a node. Attempting to
configure a bond interface in a node will only affect the parent namespace.

This change mounts a new sysfs filesystem in each node. To prevent this mount
from affecting the parent namespace the mount namespace is also unshared.

[1]: https://www.kernel.org/doc/Documentation/filesystems/sysfs-tagging.txt
This commit is contained in:
Rich Lane
2013-11-18 17:05:09 -08:00
parent bee06cf264
commit 5461565945
1 changed files with 11 additions and 5 deletions
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mnexec.c
+11 -5
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@@ -5,7 +5,7 @@
*
* - closing all file descriptors except stdin/out/error
* - detaching from a controlling tty using setsid
* - running in a network namespace
* - running in network and mount namespaces
* - printing out the pid of a process so we can identify it later
* - attaching to a namespace and cgroup
* - setting RT scheduling
@@ -23,6 +23,7 @@
#include <stdlib.h>
#include <sched.h>
#include <ctype.h>
#include <sys/mount.h>
#if !defined(VERSION)
#define VERSION "(devel)"
@@ -35,9 +36,9 @@ void usage(char *name)
"Options:\n"
" -c: close all file descriptors except stdin/out/error\n"
" -d: detach from tty by calling setsid()\n"
" -n: run in new network namespace\n"
" -n: run in new network and mount namespaces\n"
" -p: print ^A + pid\n"
" -a pid: attach to pid's network namespace\n"
" -a pid: attach to pid's network and mount namespaces\n"
" -g group: add to cgroup\n"
" -r rtprio: run with SCHED_RR (usually requires -g)\n"
" -v: print version\n",
@@ -122,11 +123,16 @@ int main(int argc, char *argv[])
setsid();
break;
case 'n':
/* run in network namespace */
if (unshare(CLONE_NEWNET) == -1) {
/* run in network and mount namespaces */
if (unshare(CLONE_NEWNET|CLONE_NEWNS) == -1) {
perror("unshare");
return 1;
}
/* mount sysfs to pick up the new network namespace */
if (mount("sysfs", "/sys", "sysfs", MS_MGC_VAL, NULL) == -1) {
perror("mount");
return 1;
}
break;
case 'p':
/* print pid */