Re: [Nbd] [PATCH 6/6] nbd: add a basic netlink interface

On Wed, Mar 08, 2017 at 09:56:48AM -0500, Josef Bacik wrote:

On Wed, 2017-03-08 at 11:07 +0100, Wouter Verhelst wrote:

quoted

On Tue, Feb 28, 2017 at 11:57:11AM -0500, Josef Bacik wrote:

quoted

The existing ioctl interface for configuring NBD devices is a bit
cumbersome and hard to extend.��The other problem is we leave a
userspace app sitting in it's syscall until the device disconnects,
which is less than ideal.

True.

On the other hand, it has the advantage that you leave a userspace
app
sitting around until the device disconnects, which allows for some
form
of recovery in case you're doing root-on-NBD and the server has a
hiccup. Don't underestimate the advantage of that.

(of course, that requires that the return value of NBD_DO_IT makes a
difference between "unexpected connection drop" and "we sent
NBD_CMD_DISC", but that's a different matter entirely)

Stay tuned for further developments ;).

Heh.

Yeah the problem is that even
though we can return and allow the user to reconnect, we completely
tear down the device and will return EIO to anything that comes in
while we're reconnecting, which sucks for users.

Quite, yes.

�The patches that I'm testing now will multi-cast messages over netlink
when a link goes down so a user space application can reconnect and
provide a new connection seamlessly. �The next step after that is to
allow a complete failure of all connections and we will simply sit
there and queue IO until userspace reconnects or the configured
timeout elapses at which point we'll tear down the device. �The end
goal of all of this is seamless reconnects without throwing errors.

Awesome. That would mean userspace would need to sit around, but I
suppose that isn't something we can't live with (and actually has other
advantages, too).

Thanks,

-- 
< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12