linux-ext4 - Re: [RFC 1/4] fs: Add generic file system event notifications

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Message-ID: <20150417134144.GA23905@quack.suse.cz>
Date:	Fri, 17 Apr 2015 15:41:44 +0200
From:	Jan Kara <jack@...e.cz>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>
Cc:	Beata Michalska <b.michalska@...sung.com>, Jan Kara <jack@...e.cz>,
	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 Fri 17-04-15 09:23:35, Austin S Hemmelgarn wrote:
> On 2015-04-17 09:04, Beata Michalska wrote:
> >On 04/17/2015 01:31 PM, Jan Kara wrote:
> >>On Wed 15-04-15 09:15:44, Beata Michalska wrote:
> >>...
> >>>+static const match_table_t fs_etypes = {
> >>>+	{ FS_EVENT_INFO,    "info"  },
> >>>+	{ FS_EVENT_WARN,    "warn"  },
> >>>+	{ FS_EVENT_THRESH,  "thr"   },
> >>>+	{ FS_EVENT_ERR,     "err"   },
> >>>+	{ 0, NULL },
> >>>+};
> >>   Why are there these generic message types? Threshold messages make good
> >>sense to me. But not so much the rest. If they don't have a clear meaning,
> >>it will be a mess. So I also agree with a message like - "filesystem has
> >>trouble, you should probably unmount and run fsck" - that's fine. But
> >>generic "info" or "warning" doesn't really carry any meaning on its own and
> >>thus seems pretty useless to me. To explain a bit more, AFAIU this
> >>shouldn't be a generic logging interface where something like severity
> >>makes sense but rather a relatively specific interface notifying about
> >>events in filesystem userspace should know about so I expect relatively low
> >>number of types of events, not tens or even hundreds...
> >>
> >>								Honza
> >
> >Getting rid of those would simplify the configuration part, indeed.
> >So we would be left with 'generic' and threshold events.
> >I guess I've overdone this part.
> 
> 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.
   Sure, but in that case just create an event CORRECTED_CHECKSUM_ERROR and
use that. Then userspace knows what it should do with the event. No need to
hide it behind warning / error category.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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