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Re: [Qemu-devel] [PATCH v2 0/3] block: Correct size across CD-ROM media

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH v2 0/3] block: Correct size across CD-ROM media change
Date: Wed, 30 Mar 2011 11:06:50 +0100

On Wed, Mar 30, 2011 at 9:33 AM, Markus Armbruster <address@hidden> wrote:
> Stefan Hajnoczi <address@hidden> writes:
>> This patch series fixes two Linux host CD-ROM pass-through bugs in QEMU.
>> After applying these patches it is possible to pass-through a Linux host 
>> completely.  The guest can eject from software or the physical eject button 
>> can
>> be pressed on the drive.  The guest can detect this and newly inserted media
>> are noticed.  There is no need to issue any QEMU monitor 'eject' or 'change'
>> commands because the host CD-ROM is completely "passed through".
> Things can get confusing here, as "eject" is an overloaded term :)
> Let me try to preempt such confusion.  We have three separate actions to
> consider: OS opening and closing the tray, and QEMU monitor commands
> "eject" and "change", and the user inserting/removing media from a
> physical tray.
> On bare metal, OS open/close tray affects the physical tray the obvious
> way.  The user can insert/remove media while the tray is open.
> A virtual CD-ROM is backed by a QEMU block device (the things "info
> block" shows).  The block device can be empty (seen by the gues OS as
> "no media"), or it can be connected to a file.  Monitor commands "eject"
> and "change" manipulate that connection.
> Guest OS open/close tray affects the virtual tray the obvious way.  In
> particular, if the OS opens, then closes the tray, it gets the same
> media back, unless the user changed it[*].
> Normally, a block device's file is an image file.  Monitor commands
> "eject" and "change" are seen by the guest OS as media change.
> Besides image files, we can also use host block devices.  This adds
> another way to change media: The user can insert/remove physical media
> while the physical tray is open.
> Regardless, monitor commands "eject" and "change" still work, and are
> still seen by the guest OS as media change.

I agree with your description.

These patches improve Linux host CD-ROM pass-through.  They do not
help ISO CD-ROM weirdness but I'm interested in seeing what CD-ROM
issues you're investigating.


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