linux-kernel - Re: [RFC 1/4] fs: Add generic file system event notifications

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Date:	Fri, 17 Apr 2015 17:08:10 +0100
From:	John Spray <john.spray@...hat.com>
To:	Jan Kara <jack@...e.cz>
CC:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Beata Michalska <b.michalska@...sung.com>,
	linux-kernel@...r.kernel.org, tytso@....edu,
	adilger.kernel@...ger.ca, hughd@...gle.com, lczerner@...hat.com,
	hch@...radead.org, linux-ext4@...r.kernel.org, linux-mm@...ck.org,
	kyungmin.park@...sung.com, kmpark@...radead.org,
	Linux Filesystem Mailing List <linux-fsdevel@...r.kernel.org>,
	linux-api@...r.kernel.org
Subject: Re: [RFC 1/4] fs: Add generic file system event notifications


On 17/04/2015 16:43, Jan Kara wrote:
> On Fri 17-04-15 15:51:14, John Spray wrote:
>> On 17/04/2015 14:23, Austin S Hemmelgarn wrote:
>>
>>> For some filesystems, it may make sense to differentiate between a
>>> generic warning and an error.  For BTRFS and ZFS for example, if
>>> there is a csum error on a block, this will get automatically
>>> corrected in many configurations, and won't require anything like
>>> fsck to be run, but monitoring applications will still probably
>>> want to be notified.
>> Another key differentiation IMHO is between transient errors (like
>> server is unavailable in a distributed filesystem) that will block
>> the filesystem but might clear on their own, vs. permanent errors
>> like unreadable drives that definitely will not clear until the
>> administrator takes some action.  It's usually a reasonable
>> approximation to call transient issues warnings, and permanent
>> issues errors.
>    So you can have events like FS_UNAVAILABLE and FS_AVAILABLE but what use
> would this have? I wouldn't like the interface to be dumping ground for
> random crap - we have dmesg for that :).
In that case I'm confused -- why would ENOSPC be an appropriate use of 
this interface if the mount being entirely blocked would be 
inappropriate?  Isn't being unable to service any I/O a more fundamental 
and severe thing than being up and healthy but full?

Were you intending the interface to be exclusively for data integrity 
issues like checksum failures, rather than more general events about a 
mount that userspace would probably like to know about?

John
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