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Date: Mon, 11 Jan 2016 19:59:21 +0000
From: Keith Busch <keith.busch@intel.com>
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Subject: Re: [Qemu-devel] [Bug 1529449] [NEW] serial is required for -device
 nvme
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To: Markus Armbruster <armbru@redhat.com>
Cc: Bug 1529449 <1529449@bugs.launchpad.net>, qemu-devel@nongnu.org, Tom Yan <tom.ty89@gmail.com>

On Mon, Jan 11, 2016 at 05:35:50PM +0100, Markus Armbruster wrote:
> Tom Yan <tom.ty89@gmail.com> writes:
> > Public bug reported:
> >
> > I am not exactly sure if this is a bug, but I don't see why the option
> > "serial" should be required for -device nvme like the option "drive".
> > Truth is it seem to accept random string as its value anyway, if that's
> > the case, couldn't qemu just generate one for it when it's not
> > specified?
>
> You should've included a reproducer.  Here are mine:
> 
> 1. Bad error reporting on missing drive:
> 
>      $ upstream-qemu -nodefaults -device nvme
>      upstream-qemu: -device nvme: Device initialization failed
> 
>    Expected: error reported like for other devices, e.g.
> 
>      $ upstream-qemu -nodefaults -device virtio-blk
>      upstream-qemu: -device virtio-blk: drive property not set
> 
> 2. Bad error reporting on empty drive:
> 
>      $ upstream-qemu -nodefaults -drive if=none,id=foo -device nvme,drive=foo
>      upstream-qemu: -device nvme,drive=foo: Device initialization failed
> 
>    Expected: error is reported like for other devices, e.g.
> 
>      $ upstream-qemu -nodefaults -drive if=none,id=foo -device virtio-blk,drive=foo
>      upstream-qemu: -device virtio-blk,drive=foo: Device needs media, but drive is empty
> 
> 3. Bad handling of missing serial:
> 
>       $ upstream-qemu -nodefaults -drive if=none,id=foo,file=tmp.qcow2 -device nvme,drive=foo
>       upstream-qemu: -device nvme,drive=foo: Device initialization failed
> 
>    Expected: either default the serial number, like some other devices
>    do, or a decent error message.
> 
> I recommend to convert the device to realize(), and add the missing
> error_setg().  Keith?

Requiring a serial was a concious choice to push that responsibility
on the user, but I don't see a problem having the code provide default
serial string if the user does not over ride it.

If you've multiple nvme devices in your guest, creating the same serial
could cause problems with multipathing if they're basing end device
uniqueness on the serial (some do). If we have the code provide the
serial, perhaps it would be best to make each unique. That's easy enough
to append an incrementing number to the end of the serial.