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

From: Fam Zheng
Subject: Re: [Qemu-devel] [PATCH 3/7] nbd: use BDS refcount
Date: Wed, 3 Jul 2013 14:30:30 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Wed, 07/03 07:58, Paolo Bonzini wrote:
> 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.

But drive_put_ref is called by close notifier. I think it can be
omitted, registering a close notifier is enough, and close the export
when drive_del calls it. It doesn't make more sense w/ drive_get_ref,
does it?


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