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

On 04/17/2015 06:08 PM, John Spray wrote:

On 17/04/2015 16:43, Jan Kara wrote:

quoted

On Fri 17-04-15 15:51:14, John Spray wrote:

quoted

On 17/04/2015 14:23, Austin S Hemmelgarn wrote:

quoted

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

I think we should support both and leave the decision on what
is to be reported or not to particular file systems keeping it
to a reasonable extent, of course. The interface should hand it over
to user space - acting as a go-between. I would though avoid
any filesystem specific events (when it comes to specifying those),
keeping it as generic as possible.


BR
Beata