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SubjectRe: RFC: Devices, buses and hotplug
Hello,

> Hmm, as long as we don't have fds[1] that could die gracefully
> and applications that could handle this...
>
> ... I would call this _impossible_
>
> The thing is, that a fd is valid from sucessful open to
> sucessful close. So everything this fd depends on, is open too.
>
> But we could introduce a new signal (bad, since not POSIX), or
> use a new semantic for an existing one (even worse) to say "Hey,
> this fd is dead now! Any use from now on will cause errors."

I think we need no new signals. All what we need is to revoke
all file handles connected to the device having been unplugged.

> Another simplier problem is, if the ressource is _temporarly_
> unavailable[2].

The question is whether we really want to handle such situation
without userland noticing the exchange or whether the right view
is "the old device ceased to exist, a new one appeared with the
same name, all programs need to re-open it."

(Please note that in the most common cases, i.e. swapping of disks
in a disk array or replacing faulty network cards, the exchange can
be fully transparent even without introducing any additional mechanisms
and without userland programs noticing it.)

Have a nice fortnight
--
Martin `MJ' Mares <mj@ucw.cz> http://atrey.karlin.mff.cuni.cz/~mj/
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
"This message transmited on 100% recycled electrons."

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