Re: [Qemu-devel] [PATCH 2/2] filemon: ensure watch IDs are unique to QFileMonitor scope

[Bandan Das]

Daniel P. Berrangé <address@hidden> writes:
...
>> Thanks, this fixes it! I had a related question about the way
>> qemu_file_monitor_add_watch works.
>> 
>> Am I correct in understanding that if there is already a watch on a dir,
>> we return back mon->nextid++ i.e the next free id. Why don't we return
>> back the originally assigned watchid ?
>
> inotify watches are a per-directory scope thing, but this API is aiming
> to present the ability to have per-file scope watches as it is more
> convenient to have those semantics for some users in QEMU. Thus many
> QEMU level watches are mapped to the same low level inotify watch.
>
> The watch ID is used to unregister a watch later, and while I could have
> done ref counting against a common watch ID, I find it clearer to maintain
> separate watch IDs for every thing the caller watches. If nothing else it
> makes the debugging easier as you can see the relation between events
> received and the original watch registration.
>
Thanks, this makes sense. I think an advantage of having a refcounting
mechanism is that we won't run out of watchids because some caller
ended up adding a watch on the same dir repeatedly.

> Regards,
> Daniel