linux-kernel - Re: [PATCH 3/4] autofs - make mountpoint checks namespace aware

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Date:   Mon, 26 Sep 2016 11:05:23 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Ian Kent <raven@...maw.net>
Cc:     Mateusz Guzik <mguzik@...hat.com>, NeilBrown <neilb@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Omar Sandoval <osandov@...ndov.com>
Subject: Re: [PATCH 3/4] autofs - make mountpoint checks namespace aware

Ian Kent <raven@...maw.net> writes:

> On Fri, 2016-09-23 at 14:15 -0500, Eric W. Biederman wrote:
>> Ian Kent <raven@...maw.net> writes:
>> 
>> 2> On Thu, 2016-09-22 at 20:37 -0500, Eric W. Biederman wrote:
>> > > Ian Kent <raven@...maw.net> writes:
>> > > 
>> > > > On Thu, 2016-09-22 at 10:43 -0500, Eric W. Biederman wrote:
>> > > > > Ian Kent <raven@...maw.net> writes:
>> > > > > 
>> > > > > > Eric, Mateusz, I appreciate your spending time on this and
>> > > > > > particularly
>> > > > > > pointing
>> > > > > > out my embarrassingly stupid is_local_mountpoint() usage mistake.
>> > > > > > 
>> > > > > > Please accept my apology for the inconvenience.
>> > > > > > 
>> > > > > > If all goes well (in testing) I'll have follow up patches to correct
>> > > > > > this
>> > > > > > fairly
>> > > > > > soon.
>> > > > > 
>> > > > > Related question.  Do you happen to know how many mounts per mount
>> > > > > namespace tend to be used?  It looks like it is going to be wise to
>> > > > > put
>> > > > > a configurable limit on that number.  And I would like the default to
>> > > > > be
>> > > > > something high enough most people don't care.  I believe autofs is
>> > > > > likely where people tend to use the most mounts.
>> > 
>> > Yes, I agree, I did want to try and avoid changing the parameters to
>> > ->d_mamange() but passing a struct path pointer might be better in the long
>> > run
>> > anyway.
>> 
>> Given that there is exactly one implementation of d_manage in the tree I
>> don't imagine it will be disruptive to change that.
>
> Yes, but it could be used by external modules.
>
> And there's also have_submounts().

Good point about have_submounts.

> I can update that using the existing d_walk() infrastructure or take it (mostly)
> into the autofs module and get rid of have_submounts().
>
> I'll go with the former to start with and see what people think.

That will be interesting to so.  It is not clear to me that if d_walk
needs to be updated, and if d_walk doesn't need to be updated I would
be surprised to see it take into autofs.  But I am happy to look at the
end result and see what you come up with.

Eric