Re: [Devel] [PATCH 2/2] sys_restore: set the pid number

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Pavel Emelyanov (xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org):
> Serge E. Hallyn wrote:
> > Set the pid number for a restored task.  This is purely a toy, as it
> > only sets the pidnr in the lowest level pid namespace.
> > 
> > Signed-off-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> > ---
> >  kernel/fork.c |    5 +++++
> >  kernel/pid.c  |   19 +++++++++++++++++++
> >  2 files changed, 24 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 0e43f69..41c46d2 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -1685,6 +1685,8 @@ int unshare_files(struct files_struct **displaced)
> >  char buf[CKPT_SIZE];
> >  char exe_filename[PAGE_SIZE];
> >  
> > +extern int choose_pidmap(struct pid *pid, int new);
> > +
> >  /*
> >   * userspace will already have made us a new pidns
> >   */
> > @@ -1717,6 +1719,9 @@ long do_restore(unsigned int fd,
> >  	if (nr_scanned != 2)
> >  		return -EINVAL;
> >  
> > +	ret = choose_pidmap(task_pid(current), pid);
> > +	if (!ret)
> > +		return -EAGAIN;
> >  
> >  	ret = do_execve(exe_filename, argv, envp, regs);
> >  out:
> > diff --git a/kernel/pid.c b/kernel/pid.c
> > index 30bd5d4..88a5e2a 100644
> > --- a/kernel/pid.c
> > +++ b/kernel/pid.c
> > @@ -122,6 +122,25 @@ static void free_pidmap(struct upid *upid)
> >  	atomic_inc(&map->nr_free);
> >  }
> >  
> > +int choose_pidmap(struct pid *pid, int new)
> > +{
> > +	struct pidmap *map;
> > +	int level = pid->level;
> > +	struct upid *upid = &pid->numbers[level];
> > +	struct pid_namespace *pid_ns = upid->ns;
> > +	int old = upid->nr;
> > +
> > +	map = &pid_ns->pidmap[new/BITS_PER_PAGE];
> > +	if (!test_and_set_bit(new, map->page)) {
> 
> This and...
> 
> > +		map = &pid_ns->pidmap[old/BITS_PER_PAGE];
> > +		clear_bit(old, map->page);
> 
> this are both a bit buggy, since the bit number on the page
> is not the same as the pid id itself ;)

Oops.  Yes, I see.

thanks,
-serge

> > +		upid->nr = new;
> > +		return 1;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int alloc_pidmap(struct pid_namespace *pid_ns)
> >  {
> >  	int i, offset, max_scan, pid, last = pid_ns->last_pid;