linux-ext4 - Re: [PATCH v2 0/2] ext4: Add pollable sysfs entry for block threshold events

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Date:	Wed, 18 Mar 2015 11:12:24 +0100 (CET)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Beata Michalska <b.michalska@...sung.com>
cc:	Christoph Hellwig <hch@...radead.org>, adilger.kernel@...ger.ca,
	tytso@....edu, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com
Subject: Re: [PATCH v2 0/2] ext4: Add pollable sysfs entry for block threshold
 events

On Wed, 18 Mar 2015, Beata Michalska wrote:

> Date: Wed, 18 Mar 2015 10:31:01 +0100
> From: Beata Michalska <b.michalska@...sung.com>
> To: Christoph Hellwig <hch@...radead.org>
> Cc: lczerner@...hat.com, adilger.kernel@...ger.ca, tytso@....edu,
>     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
>     kyungmin.park@...sung.com
> Subject: Re: [PATCH v2 0/2] ext4: Add pollable sysfs entry for block threshold
>      events
> 
> On 03/16/2015 02:28 PM, Christoph Hellwig wrote:
> > Between this and the recent tmpfs discussion I really think this
> > needs to be done in a generic way.  Given that the quota noticiations
> > already use netlink general space notifications seem like a very
> > sensible extension for them.
> > 
> 
> First of all, apologies for late response.
> 
> I do agree that having a generic solution is the perfect one
> though non-trivial. If I understood You correctly, You would
> like to have quota being extended to cover the case in subject;
> smth similar to xfs project quota and its pqnoenforce mount
> option, as this would require disabling enforcing both:
> soft and hard limits ?

As Jan already mentioned the problem with quota is that it really
is accounting for used space per user, which is not really ideal for
this scenario. I have not seen the tmpfs discussions so maybe
they have a solution ?

Also, implementing noenforce should should be relatively easy.

> 
> 
> We could also consider going back to already mentioned,
> in another thread, the netlink notification interface proposal,
> though this still leaves the problem on how to setup the thresholds
> (as it covers only the ENOSPC case).

As Ted mentioned in one of his replies, filesystem would have to
support it at some level. Probably setting a value within a
superblock and then check against this value.

The netlink notification interface would then serve only as a mean
to notify the user.

Thanks!
-Lukas

> 
> 
> BR
> Beata
> 
> 
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