[CRIU] [PATCH] pipes: Restore pipe size via userns call

[Cyrill Gorcunov]

On Mon, Mar 13, 2017 at 11:44:39AM -0700, Andrei Vagin wrote:
...
> >  int restore_pipe_data(int img_type, int pfd, u32 id, struct pipe_data_rst **hash)
> >  {
> >  	int ret;
> > @@ -201,13 +221,11 @@ int restore_pipe_data(int img_type, int pfd, u32 id, struct pipe_data_rst **hash
> >  out:
> >  	ret = 0;
> >  	if (pd->pde->has_size) {
> > -		pr_info("Restoring size %#x for %#x\n",
> > -				pd->pde->size, pd->pde->pipe_id);
> > -		ret = fcntl(pfd, F_SETPIPE_SZ, pd->pde->size);
> > -		if (ret < 0)
> > -			pr_perror("Can't restore pipe size");
> > -		else
> > -			ret = 0;
> > +		pipe_set_size_arg_t args = {
> > +			.pipe_id	= pd->pde->pipe_id,
> > +			.size		= (size_t)pd->pde->size,
> > +		};
> > +		ret = userns_call(pipe_set_size, UNS_ASYNC, &args, sizeof(args), pfd);
> 
> UNS_ASYNC is used to improve perfomance, isn't it? If it is, I would
> suggest to try to set a pipe size here and make userns_call only if it is failed
> with EPERM. In this case we can do this synchroniously, because the
> number of these calls probably will be small. And you will be able to
> apply Pavel's comment.

Which would bloat code size :/ Drop it. Hopefully I'll code with
some better idea.