On Thu, 2017-05-11 at 11:10 -0700, Andy Grover wrote: > > I think getting one readiness notification for multiple events should > be ok. > > But, the semantics of poll(2) are level-triggered, meaning if a fd > is > ready then it will stay ready through multiple invocations of poll() > until something is done to satisfy it (e.g. for a TCP socket, > read()ing > all the available data). Therefore we can't make it "edge-triggered" > by > auto-clearing - it has to be a separate action. Hm, perhaps. Here is an idea: the best way to avoid the race mentioned by Mike might be to set priv->global_event_nr to the highest event nr reported by the DM_LIST_DEVICES ioctl when this ioctl returns. DM_LIST_DEVICES would then represent your "separate action", which would fit quite well, and the DM_DEV_ARM_POLL ioctl wouldn't be needed. It would be guaranteed that if any event had occured after the previous DM_LIST_DEVICES, whether or not that had been before or after the poll() call, userspace would notice. Cheers, Martin -- Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
