[CRIU] [PATCH 2/2] restore: remount /proc after clone(CLONE_NEWPID)

[Andrew Vagin]

On Fri, Aug 08, 2014 at 02:45:04PM +0400, Pavel Emelyanov wrote:
> On 08/08/2014 01:57 PM, Andrew Vagin wrote:
> > On Thu, Aug 07, 2014 at 08:46:19AM -0500, Tycho Andersen wrote:
> >> On Thu, Aug 07, 2014 at 10:08:06AM +0400, Pavel Emelyanov wrote:
> >>> On 08/07/2014 07:33 AM, Tycho Andersen wrote:
> >>>> Isn't it still a bug not to re-mount /proc though?
> >>>
> >>> If we don't create new mount namespace, then re-mounting seem like bug --
> >>> if we change the way information is represented in it for root (init) task
> >>> we restore, then we change the way it looks for the tasks living in the
> >>> pid namespace criu was launched in.
> >>
> >> Yep, agreed.
> >>
> >>>> Or, I guess it
> >>>> isn't totally a bug, as long as you don't look in /proc, but criu
> >>>> seems to do that a lot. 
> >>>
> >>> It does, but it should do all the proc stuff via proc service descriptor.
> >>> The open_proc, fopen_proc and others do exactly this.
> >>>
> >>> Do you know any places where criu just goes and accesses "/proc/..."?
> >>
> >> Ah, I didn't realize those would poke at the right /proc, that is
> >> handy :). Yes, parse_mountinfo looks in /proc directly. However, when I do
> >> this:
> >>
> >> diff --git a/proc_parse.c b/proc_parse.c
> >> index 3da5445..68d932b 100644
> >> --- a/proc_parse.c
> >> +++ b/proc_parse.c
> >> @@ -944,8 +944,7 @@ struct mount_info *parse_mountinfo(pid_t pid, struct ns_id *nsid)
> >>         FILE *f;
> >>         char str[1024];
> >>  
> >> -       snprintf(str, sizeof(str), "/proc/%d/mountinfo", pid);
> >> -       f = fopen(str, "r");
> >> +       f = fopen_proc(pid, "mountinfo");
> >>         if (!f) {
> >>                 pr_perror("Can't open %d mountinfo", pid);
> >>                 return NULL;
> >>
> >> I still get Error (mount.c:1952): New root and old root are the same.
> > 
> > Tycho, look at the attached patch. This patch uses /proc/self/mountinfo
> > to collect mounts for the root task on restore.
> 
> Why doesn't fopen_proc() work?

Because we should use PROC_SELF

> 
> > Thanks.
> > 
> > 
> >>
> >> Tycho
>