linux-kernel - Re: [GIT PULL] Mount and superblock notifications

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Message-ID: <20200405225240.kofadjkmpigfzcfy@alap3.anarazel.de>
Date:   Sun, 5 Apr 2020 15:52:40 -0700
From:   Andres Freund <andres@...razel.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, dray@...hat.com,
        Karel Zak <kzak@...hat.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>, jlayton@...hat.com,
        Ian Kent <raven@...maw.net>,
        Christian Brauner <christian.brauner@...ntu.com>,
        keyrings@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Mount and superblock notifications

Hi,

On 2020-04-04 14:13:03 -0700, Linus Torvalds wrote:
> And it needs to be interesting and pressing enough that those people
> actually at least do a working prototype on top of a patch-set that
> hasn't made it into the kernel yet.
> 
> Now, I realize that other projects won't _upstream_ their support
> before the kernel has the infrastructure, so I'm not looking for
> _that_ kind of "yeah, look, project XYZ already does this and Red Hat
> ships it". No, I'm looking for those outside developers who say more
> than "this is a pet peeve of mine with the existing interface". I want
> to see some actual use - even if it's just in a development
> environment - that shows that it's (a) sufficient and (b) actually
> fixes problems.

FWIW, postgres remains interested in using the per-superblock events.

On 2020-03-30 15:36:54 +0100, David Howells wrote:
>  (2) Superblock notifications.
> 
>      This one is provided to allow systemd or the desktop to more easily
>      detect events such as I/O errors and EDQUOT/ENOSPC.  This would be of
>      interest to Postgres:
> 
> 	https://lore.kernel.org/linux-fsdevel/20200211005626.7yqjf5rbs3vbwagd@alap3.anarazel.de/
> 
>      But could also be used to indicate to systemd when a superblock has
>      had its configuration changed.

What prevents me from coming up with a prototype is that the error
handling pieces aren't complete, as far as I can tell:

On 2020-03-30 15:36:54 +0100, David Howells wrote:
>  (2) Superblock events, such as R/W<->R/O changes, quota overrun and I/O
>      errors (not complete yet).

There's afaict no notify_sb_error() callers, making it hard for me to
actually test anything.

The important issue for us is I/O errors, but EDQUOT/ENOSPC could also
be useful (but is not urgent).

Greetings,

Andres Freund