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

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On 17/04/2015 14:23, 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.

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.

John




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