linux-kernel - Re: Why add the general notification queue and its sources

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Message-ID: <CAKCoTu7ms_Mr-q08d9XB3uascpzwBa5LF9JTT2aq8uUsoFE8aQ@mail.gmail.com>
Date:   Thu, 5 Sep 2019 14:32:40 -0400
From:   Ray Strode <rstrode@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Howells <dhowells@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>, raven@...maw.net,
        keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-block <linux-block@...r.kernel.org>,
        Christian Brauner <christian@...uner.io>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Ray, Debarshi" <debarshi.ray@...il.com>,
        Robbie Harwood <rharwood@...hat.com>
Subject: Re: Why add the general notification queue and its sources

Hi,

On Thu, Sep 5, 2019 at 1:20 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> You've at least now answered part of the "Why", but you didn't
> actually answer the whole "another developer" part.
It's certainly something we've wanted in the GNOME world for a long time:

See for instance

https://bugzilla.redhat.com/show_bug.cgi?id=991110

and

https://bugzilla.gnome.org/show_bug.cgi?id=707402

from all the way back 2013.  These are the alternatives I can think of:

- poll? status quo, but not great for obvious wakeup reasons
- use a different credential cache collection type that does support
change notification?
some of the other types do support change notification, but have their
own set of
problems. But maybe we should just go back to DIR type credential
cache collections
and try to figure out the life cycle problems they pose, i don't
know... or get more
man power behind KCM...
- manage change notification entirely from userspace.  assume credentials will
always be put in place from krb5-libs entry points, and just skip
notification if
it happens out from under the libraries. maybe upstream kerberos guys would
be onboard with this, I don't know. This seems less robust than having
the kernel
in the loop, though.

> I really don't like how nobody else than you seems to even look at any
> of the key handling patches. Because nobody else seems to care.
I've got no insight here, so i'll just throw a dart...

viro, is this something you have any interest in watching closer?

> See what I'm saying? This whole "David Howells does his own features
> that nobody else uses" needs to stop. You need to have a champion. I
> just don't feel safe pulling these kinds of changes from you, because
> I get the feeling that ABSOLUTELY NOBODY ELSE ever really looked at it
> or really cared.
I get the "one man is not enough for proper maintenance" argument, and
maybe it's true.  I don't know.

But I just want to point out, I have been asking dhowells for this change
notification API for years, so it's not something he did on his own and for
no particularly good reason. It solves a real problem and has a real-world
use case.

He kindly did it because I (and Robbie Harwood and others) asked him about
it, off and on, and  he was able to fit it onto his priority list for us.
>From this thread, it sounds like he solved a problem for Greg too, killing a
couple birds with one stone?

--Ray