Re: [Qemu-devel] [PATCH v2 0/3] blockdev: Defer creation of implicit PCI devices for IF_VIRTIO drives

[Markus Armbruster]

Peter Maydell <address@hidden> writes:

> On 9 June 2015 at 18:48, Peter Maydell <address@hidden> wrote:
>> Patch 3 is the one-liner to change the default-drive-type. Unfortunately
>> just doing that alone will break commandlines that currently work
>
> The other problem with taking patch 3 alone is that it completely
> breaks everything, because:
>  * by default we create a "cdrom" drive whose type is <board-default>
>    and which has no media inserted
>  * the virtio-blk device barfs if you give it a drive with no media:
>    "Device needs media, but drive is empty"
>
> The S390 systems get around this by specifying no_cdrom = 1, but
> it doesn't seem terribly satisfactory that this has to be manually
> done by any machine with a virtio default drive type...

In my opinion, no_cdrom, no_parallel, no_floppy and no_sdcard are all
daft.  Flip their sense, and the chance of boards getting them right
increases sharply.  An explicit mc->use_cdrom = 1 in a machine
initialization function for a board without a suitable controller sticks
out and gets fixed.  A missing mc->use_cdrom = 1 for a board with a
suitable controller annoys users and gets fixed.