Re: FSEventsCopyUUIDForDevice() occasionally changes value
Re: FSEventsCopyUUIDForDevice() occasionally changes value
- Subject: Re: FSEventsCopyUUIDForDevice() occasionally changes value
- From: Dominic Giampaolo <email@hidden>
- Date: Fri, 20 Nov 2015 07:09:22 -0500
> I was doing some debugging today and I noticed that FSEventsCopyUUIDForDevice() occasionally returns a different value for a given device. The frequency varies, but the UUID seems to change about every week or so. This apparently has been going on for years.
>
> Is this expected behavior?
>
It's expected if something causes fseventsd to lose track of events and thus reset its history. The main reasons fseventsd can lose track of events is if the system crashes or reboots unexpectedly. An event overrun or fseventsd itself crashing can also cause it but that's pretty rare. The other thing that can cause it is if a volume is modified by someone other than an fseventsd capable system. In that case we don't know what changed and thus have to toss the history and generate a new volume uuid.
Generally fseventsd will print a log message when this happens. Check your recent system logs to see if there are any messages.
Note that the uuid returned by FSEventsCopoyUUIDForDevice() is not at all related to the per-volume uuid vended by through the DiskArb api's.
--dominic
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