Detecting changes when mapping /dev/devstat

[Shea Levy]

Hi all,

What is the appropriate way to detect changes when accessing devstat
info via a mapping of /dev/devstat? I'm interested both in changes to
the device list as a whole and new statistics on a given device.

For new stats on a given device, it seems the only way to detect a new
stat is to check the sequence number for that device. Is that right?

For changes in the device list, it's a bit less clear. My hope was that
I could map space for one more struct devstat than the current numdevs
and just check to see if some field or other is nonzero, but in my
glances through subr_devstat.c I'm not sure if there are any guarantees
about those fields for structures past the current list, especially if a
device was added and removed. Is there anything doable here?

Thanks,
Shea

P.S. I wasn't quite sure which list was appropriate for this question,
please feel free to point me to another!
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