From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
To: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Cc: Alexey Gladkov
<gladkov.alexey-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Linux Kernel Mailing List
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Kirill A. Shutemov"
<kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>,
Vasiliy Kulikov <segoon-cxoSlKxDwOJWk0Htik3J/w@public.gmane.org>,
"Eric W. Biederman"
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Pavel Emelyanov <xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>,
James Bottomley
<James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>
Subject: Re: [RFC] Add option to mount only a pids subset
Date: Mon, 13 Mar 2017 13:27:33 +0000 [thread overview]
Message-ID: <20170313132732.GR29622@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CALCETrVT5sfGhNomLKAephrSGj8fc81ZjGTN-Y6UwgAHngVRCA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Sun, Mar 12, 2017 at 08:19:33PM -0700, Andy Lutomirski wrote:
> On Sat, Mar 11, 2017 at 6:13 PM, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org> wrote:
> > PS: AFAICS, simple mount --bind of your pid-only mount will suddenly
> > expose the full thing. And as for the lifetimes making no sense...
> > note that you are simply not freeing these structures of yours.
> > Try to handle that and you'll get a serious PITA all over the
> > place.
> >
> > What are you trying to achieve, anyway? Why not add a second vfsmount
> > pointer per pid_namespace and make it initialized on demand, at the
> > first attempt of no-pid mount? Just have a separate no-pid instance
> > created for those namespaces where it had been asked for, with
> > separate superblock and dentry tree not containing anything other
> > that pid-only parts + self + thread-self...
>
> Can't we just make procfs work like most other filesystems and have
> each mount have its own superblock? If we need to do something funky
> to stat() output to keep existing userspace working, I think that's
> okay.
First of all, most of the filesystems do *NOT* guarantee anything of
that sort. And what's the point of having more instances than
necessary, anyway?
> As far as I can tell, proc_mnt is very nearly useless -- it seems to
> be used for proc_flush_task (which claims to be purely an optimization
> and could be preserved in the common case where there's only one
> relevant mount) and for sysctl_binary. For the latter, we could
> create proc_mnt but make actual user-initiated mounts be new
> superblocks anyway.
Again, what for? It won't salvage that kludge... It's not as if it
had been hard to have separate pid-only instance created when asked
for (and reused every time when we are asked for pid-only). What's
the point of ever having more than two instances per pidns? IDGI...
Folks, there is no one-to-one correspondence between mountpoints and
superblocks. Not since 2000 or so. Just don't try to shove your
per-superblock stuff into vfsmount; it simply won't work. If you
want a separate instance for that thing, then just go ahead and
have ->mount() decide which one to use (and whether to create a new
one). All there is to it...
next prev parent reply other threads:[~2017-03-13 13:27 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170221145746.GA31914@redhat.com>
[not found] ` <20170221145746.GA31914-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-06 23:05 ` [RFC] Add option to mount only a pids subset Alexey Gladkov
2017-03-07 16:24 ` Andy Lutomirski
2017-03-09 11:26 ` Djalal Harouni
[not found] ` <CAEiveUczqzHZG7jcM72oWXAKYZSPJ0ywYEXGDV1sn_FAhr28pA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-09 20:52 ` Eric W. Biederman
2017-03-11 21:51 ` Alexey Gladkov
[not found] ` <CALCETrVFnSoBP+LvyjN+1qUqrwgZan1nvscq5hV0Ujt_FF2e3g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-11 0:05 ` Alexey Gladkov
2017-03-07 17:49 ` Oleg Nesterov
[not found] ` <20170307174909.GA24112-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-10 23:46 ` Alexey Gladkov
2017-03-12 1:54 ` Al Viro
[not found] ` <20170312015430.GO29622-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2017-03-12 2:13 ` Al Viro
[not found] ` <20170312021257.GP29622-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2017-03-13 3:19 ` Andy Lutomirski
[not found] ` <CALCETrVT5sfGhNomLKAephrSGj8fc81ZjGTN-Y6UwgAHngVRCA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-13 13:27 ` Al Viro [this message]
[not found] ` <20170313132732.GR29622-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2017-03-13 15:24 ` Andy Lutomirski
[not found] ` <CALCETrXqv8VUeO6MpKWDR6DFYBgmmT0nZVezBJsimtmmQgDksw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-23 15:59 ` [PATCH] proc: allow to change proc mount options per mount Djalal Harouni
2017-03-20 12:58 ` [RFC] Add option to mount only a pids subset Alexey Gladkov
2017-03-23 16:05 ` Oleg Nesterov
[not found] ` <20170323160507.GA23135-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-23 22:57 ` Alexey Gladkov
2017-03-23 16:06 ` Djalal Harouni
2017-03-23 22:07 ` Alexey Gladkov
2017-03-26 7:03 ` Djalal Harouni
[not found] ` <CAEiveUe15YvZ4hMYSPgm586MkJ20PO515r9krXdjPCUmrG1wSA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-30 21:45 ` Alexey Gladkov
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