On Tue, May 21, 2013 at 05:28:36PM +0200, Oleg Nesterov wrote:
> You know, I am puzzled. Everything looks so clear that I can't
> understand what I could miss.
>
> On 05/20, J. Bruce Fields wrote:
> >
> > On Mon, May 20, 2013 at 05:10:01PM +0200, Oleg Nesterov wrote:
> > > On 05/20, Stanislav Kinsbursky wrote:
> > > >
> > > OK, why nfs can't simply use this code
> > >
> > > static int umh_set_fs_root(struct subprocess_info *info, struct cred
> > > *new)
> > > {
> > > set_fs_root(current->fs, sub_info->data);
> > > return 0;
> > > }
> > >
> > > int call_usermodehelper_root(char *path, char **argv, char **envp, int
> > > wait,
> > > struct path *root)
> > > {
> > >
> > > struct subprocess_info *info;
> > >
> > > info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
> > > umh_set_fs_root, NULL,
> > > root);
> > > if (info == NULL)
> > > return -ENOMEM;
> > > return call_usermodehelper_exec(info, wait);
> > > }
> >
> > Right, that's more or less what Stanislav proposed before:
> >
> > https://patchwork.kernel.org/patch/2449081/
> >
> > (though with an open-coded set_fs_root). Jeff and I asked him to try
> > this approach instead.
>
> And I still can't understand why you do not like this.
>
> > > ? Why do you want to add the new member, the new arguments, the new
> > > helpers?
> >
> > - It's simpler for callers to be able to say "run this help in
> > that namespace" in a single line. We expect there will be
> > more such callers, so the mild complication of the API seems
> > worth it for the convenience.
>
> So call_usermodehelper_root() above doesn't look as a simple API for you?
>
> Add it into kmod.c (or another place) and use it everywhere, why do
> insist we should complicate the generic code?
>
> What if someone wants to, say, change "nice" before running the helper?
> Do you think that we need yet another change which turns
> call_usermodehelper_setup_root() added by this patch into
> call_usermodehelper_setup_root_nice()? And another member in sub_info?
> And the "if (sub_info->nice)" check into ____call_usermodehelper() ?
>
> > - set_fs_root looks like something that shouldn't really be used
> > outside of a small number of well-known callers in core code.
>
> OK, so do not do this. Export the new helper.
You mean, export umh_set_fs_root() in the above?
That might be OK.
---b.
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