Re: [Qemu-devel] [PATCH 3/7] nbd: use BDS refcount

[Paolo Bonzini]

Il 03/07/2013 03:10, Fam Zheng ha scritto:
> > This has the important side effect of marking the exported disk as
> > "in_use" (to use the terms before the series).  Right now you can serve
> > a disk and, at the same time, stream it or mirror it or create a live
> > snapshot of it.
> > 
> > Do we really want to block anything for a device being served?  Perhaps
> > truncation, but maybe not even that.  The NBD server is meant to be as
> > unobtrusive as possible (in some sense NBD accesses are the same as
> > guest accesses).
> 
> OK, it is better to work like that. But I don't quite understand why was
> there drive_get_ref() on the device (w/o the series), as there's already
> a close notifier? And it just drive_put_ref() when bs is closed?

The close notifier runs when the user invokes a drive_del or eject
command from the monitor.  The drive_get_ref/drive_put_ref delays the
bdrv_delete until after nbd.c has cleaned up all the connections.

Paolo