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Re: [Qemu-devel] [PATCH 04/21] block: Add bdrv_close_all() handlers


From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH 04/21] block: Add bdrv_close_all() handlers
Date: Mon, 26 Jan 2015 15:43:16 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 2015-01-26 at 15:40, Paolo Bonzini wrote:

On 26/01/2015 20:27, Max Reitz wrote:
However, this was wrong: With the NBD attached to some BB, it
should stay attached until the NBD export is removed or the server
stopped; medium ejection should have nothing to do with this (other than
the NBD server not being able to read data while the virtual is open, if
there is one (and there is one if the NBD server is attached to the same
BB as a guest device with a tray is; which is correct behavior because
attaching an NBD server to a guest-used BB should result in the NBD
server behaving exactly the same as the guest device)).
Not entirely; use of close notifiers was on purpose.  We do not want the
NBD client to start reading data from a different medium without noticing.

If the NBD server is attached to the BDS, it should keep serving the BDS.

The problem is that it is no longer attached to the BDS, but to the BB.

If the NBD server is attached to the BB, the clients must have a way to
notice the medium change, and so far the solution was to close the
connection.  I'd be wary to change this, though I understand where you
come from.

Yes, I understand. However, I think the NBD server has to be attached to a separate BB if medium changes should not be allowed; but this would break backwards compatibility...

I think to retain compatibility we could either just do what we always did (although I find it wrong), or we could simply set up an eject blocker when attaching an NBD server to a BB. What do you think?

Max



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