On Fri, Nov 15, 2013 at 2:50 AM, Wouter Verhelst <[email protected]> wrote:
>
> I'm not sure if this has been implemented that way (that's Paul's area,
> not mine), but the intention was that the nbd kernel module would only
> do cleanup once the nbd-client process exits.
Not quite. It cleans up at the end of NBD_DO_IT ioctl, before returning to
userland to do the reconnect.
> That is, if nbd-client has
> not yet exited, that could be because it's in -persist mode and is
> trying to reconnect.
>
The -persist mode will only work if there is no ongoing I/O. With I/O
you're likely to get a kernel panic in the filesystem.
In order for nbd to seamlessly handle this situation, we'd have to do a
reconnect in-kernel (or have a callout to userland to reconnect) and then
we'd have to retry any I/Os that may have failed in the meantime (or just
let them fail, but that probably is not as useful).
The solution that Jack mentions is worth looking into -- it should at least
avoid the filesystem panics that we now have. I'll take a look...
--
Paul
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