nbd: separate out the config information
In order to properly refcount the various aspects of a NBD device we need to separate out the configuration elements of the nbd device. The configuration of a NBD device has a different lifetime from the actual device, so it doesn't make sense to bundle these two concepts. Add a config_refs to keep track of the configuration structure, that way we can be sure that we never access it when we've torn down the device. Add a new nbd_config structure to hold all of the transient configuration information. Finally create this when we open the device so that it is in place when we start to configure the device. This has a nice side-effect of fixing a long standing problem where you could end up with a half-configured nbd device that needed to be "disconnected" in order to be usable again. Now once we close our device the configuration will be discarded. Signed-off-by:Josef Bacik <jbacik@fb.com> Signed-off-by:
Jens Axboe <axboe@fb.com>
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