Re: [Qemu-devel] [PATCH 1/4] block: Warn if an if=<something> drive was also connected manually

[Peter Maydell]

On 22 June 2015 at 10:59, Markus Armbruster <address@hidden> wrote:
> What about this instead:
>
> 1. When -device creation connects a qdev_prop_drive property to a
> backend, fail when the backend has a DriveInfo and the DriveInfo has
> type != IF_NONE.  Note: the connection is made in parse_drive().

So, the reason I didn't do this is that it breaks some options
that currently work (the ones where the board doesn't pick up
the device and so there's no conflict). I preferred to make those
"continue to function, but warn", but if we're happy to make this
a hard error we could go this way.

> 2. This breaks -drive if=virtio and possibly more.  That's because for
> if=virtio, we create input for -device creation that asks to connect
> this IF_VIRTIO drive.  To unbreak it, mark the DriveInfo when we create
> such input, and make parse_drive() accept backends so marked.  To find
> the places that need to mark, examine users of option group "device".  A
> quick, sloppy grep shows a bit over a dozen candidates.  Not too bad.

How do we then tell the difference between parse_drive() being called
for the auto-created virtio device, and it then later being called as
part of connecting the drive to a manually created device?

My grep (which was for 'qemu_find_opts.*device' -- is that right?)
suggests that in fact the only case we need to care about is the
one where we auto-create the virtio device (the other grep matches
are not relevant).

> In my opinion, a board that specifies a default interface type it
> doesn't support is simply broken, and should be fixed.

I'm inclined to agree, but I bet we have a lot. It doesn't help
that the default if the machine doesn't specify anything is "IDE",
not "you can't use a default interface"...

> Even if we fix that, we could still reach this case when the board
> claims only *some* of the drives for its default type.  Example:
>
>     $ qemu-system-x86_64 -nodefaults -S -display none -drive 
> if=floppy,file=tmp.qcow2,index=99
>     Warning: Orphaned drive without device: 
> id=floppy99,file=tmp.qcow2,if=floppy,bus=0,unit=99
>
> Compare:
>
>     $ qemu-system-x86_64 -nodefaults -S -display none -drive 
> if=ide,file=tmp.qcow2,index=99
>     qemu-system-x86_64: Too many IDE buses defined (50 > 2)
>
> Crap shot.
>
> If we have boards that don't claim *any* interface type, we need to give
> them a .block_default_type that rejects -drive without an explicit if=.

We have several of these boards, yes. (for example, hw/arm/cubieboard.c)

thanks
-- PMM