On Wed, 2020-08-05 at 10:05 +0800, Ian Kent wrote:

On Tue, 2020-08-04 at 15:56 +0200, Miklos Szeredi wrote:

quoted

On Mon, Aug 03, 2020 at 02:37:50PM +0100, David Howells wrote:

quoted

Provide support for the handling of an overrun in a watch
queue.  In the
event that an overrun occurs, the watcher needs to be able to
find
out what
it was that they missed.  To this end, previous patches added
event
counters to struct mount.

So this is optimizing the buffer overrun case?

Shoun't we just make sure that the likelyhood of overruns is low
and
if it
happens, just reinitialize everthing from scratch (shouldn't be
*that*
expensive).

But maybe not possible if you are using notifications for tracking
state in user space, you need to know when the thing you have needs
to be synced because you missed something and it's during the
notification processing you actually have the object that may need
to be refreshed.

quoted

Trying to find out what was missed seems like just adding
complexity
for no good
reason.

Coming back to an actual use case.

What I said above is one aspect but, since I'm looking at this right
now with systemd, and I do have the legacy code to fall back to, the
"just reset everything" suggestion does make sense.

But I'm struggling to see how I can identify notification buffer
overrun in libmount, and overrun is just one possibility for lost
notifications, so I like the idea that, as a library user, I can
work out that I need to take action based on what I have in the
notifications themselves.

Ian