Re: [LTP] network namespaces tests cleanup

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> >> The proposed code uses /proc/<pid>/ns/* as file descriptors, so it needs
> >> at least 2.6.39 kernel and related iproute version or /usr/include
> >> recent enough to have IFLA_NET_NS_FD (so you can write your own netlink
> >> setup utility).
> > 
> > Does not seem to be the case for SLES11 SP3 nor SP4. The kernel should
> > be new enough since SP2 though.
> 
> Well, this would be a "nice to have", we could still use
> IFLA_NET_NS_PID, which you should have (also used by current test code).

This one is present.

> Your iproute could also have support for it,
>   $ ip link help 2>&1 | grep netns

                          [ netns PID ]
                          [ netns NAME ]

Seems to be the case as well.

> >> Some (most?) enterprise distributions may have the functionality
> >> backported, for example RHEL-6.6 fully supports mounting
> >> /proc/<pid>/ns/* and even has util-linux support (like nsenter(1)) for
> >> the mounted file descriptors. It is, however, missing any 'ip netns'
> >> support as well as 'ip link .. netns <file>' (supports only pid).
> >>
> >> What about others?
> >>
> >> # kernel fd (setns(2)) + util-linux support
> >> touch netnstest
> >> unshare --net mount --bind /proc/self/ns/net netnstest
> >> nsenter --net=netnstest ip link show
> > 
> > SLES11 unshare does not support --bind and does not have nsenter likely
> > util-linux is too old (2.19.1).
> 
> The --bind is not for unshare, but for mount(8). If you don't have
> unshare(1) from util-linux or have some old one (without netns support),
> try this as a quick replacement for creating the namespace, feel free
> to use mount(2) with MS_BIND (linux 2.4+) if your mount(8) doesn't
> support --bind:

Ah, right, mount supports bind without problem.

> #define _GNU_SOURCE
> #include <sched.h>
> #include <unistd.h>
> int main(int argc, char **argv)
> {
>     char *ma[] = {"mount","--bind","/proc/self/ns/net","netnstest",NULL};
>     unshare(CLONE_NEWNET);
>     execvp("mount", ma);
>     return 1;
> }

What I got:

mount("/proc/15413/ns/net", "netnstest", 0x410848, MS_MGC_VAL|MS_BIND, NULL) = -1 ENOTDIR (Not a directory)

ls -l /proc/self/ns/net
-r-------- 1 root root 0 Feb 25 13:23 /proc/self/ns/net

> and this as a replacement for nsenter:
> 
> #include <sched.h>
> #include <fcntl.h>
> #include <unistd.h>
> int main(int argc, char **argv)
> {
>     int i, fd;
> 
>     fd = open(argv[1], O_RDONLY);
>     /* provide NULL-terminated array for execve */
>     for (i = 1; i < argc-1; i++)
>         argv[i] = argv[i+1];
>     argv[i] = NULL;
> 
>     setns(fd, 0);
>     execvp(argv[1], argv+1);
>     return 1;
> }
> 
> (use as ./a.out netnstest <cmd> [args])
> 
> If it doesn't work, please try strace, doing proper error detection
> for everything above would double the necessary code.

This works after replacing setns(fd, 0) with the syscall(__NR_setns, fd, 0).

-- 
Cyril Hrubis
chrubis@suse.cz

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