From: Jan Kara Subject: Re: [RFC 1/4] fs: Add generic file system event notifications Date: Fri, 17 Apr 2015 18:22:47 +0200 Message-ID: <20150417162247.GB27500@quack.suse.cz> References: <1429082147-4151-1-git-send-email-b.michalska@samsung.com> <1429082147-4151-2-git-send-email-b.michalska@samsung.com> <20150417113110.GD3116@quack.suse.cz> <553104E5.2040704@samsung.com> <55310957.3070101@gmail.com> <55311DE2.9000901@redhat.com> <20150417154351.GA26736@quack.suse.cz> <55312FEA.3030905@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Austin S Hemmelgarn , Beata Michalska , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tytso-3s7WtUTddSA@public.gmane.org, adilger.kernel-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org, hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, lczerner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, kyungmin.park-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org, kmpark-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, Linux Filesystem Mailing List , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: John Spray Return-path: Content-Disposition: inline In-Reply-To: <55312FEA.3030905-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org On Fri 17-04-15 17:08:10, John Spray wrote: > > 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? Well, I'm not saying we cannot have those events for fs availability / inavailability. I'm just saying I'd like to see some use for that first. I don't want events to be added just because it's possible... For ENOSPC we have thin provisioned storage and the userspace deamon shuffling real storage underneath. So there I know the usecase. Honza -- Jan Kara SUSE Labs, CR