On Tue, Jun 23, 2015 at 03:01:44PM +0100, Peter Maydell wrote:
> This patchset attempts to improve the warning and error messages for
> bad user command lines that attempt to connect a drive up to two
> devices. The motivation here is patch #4, which changes the default
> interface for the virt board to virtio. That will break some existing
> command lines which forgot to specify if=none, and so I would like
> us to at least diagnose that user error in a helpful way that points
> the user towards adding the missing if=none.
> 
> Version 2 reduces scope, because it turns out that it is harder than
> we thought to identify whether a use of an if=something drive is the
> auto-plugging or a manual wiring up to a device. So all we do here
> is improve the error messages for two situations which were already
> errors but with rather cryptic messages:
> 
>     (1) Drive specified as to be auto-connected and also manually connected
>     (and the board does handle this if= type):
>     
>       qemu-system-x86_64 -nodefaults -display none \
>          -drive if=scsi,file=tmp.qcow2,id=foo -device ide-hd,drive=foo
>     
>     Previously:
>       qemu-system-x86_64: -device ide-hd,drive=foo: Property 'ide-hd.drive'
>       can't take value 'foo', it's in use
>     
>     Now:
>       qemu-system-x86_64: -device ide-hd,drive=foo: Drive 'foo' is already in
>       use because it has been automatically connected to another device (did
>       you need 'if=none' in the drive options?)
>     
>     (2) Drive specified to be manually connected in two different ways:
>     
>       qemu-system-x86_64 -nodefaults -display none \
>        -drive if=none,file=tmp.qcow2,id=foo -device ide-hd,drive=foo \
>        -device ide-hd,drive=foo
>     
>     Previously:
>       qemu-system-x86_64: -device ide-hd,drive=foo: Property 'ide-hd.drive'
>       can't take value 'foo', it's in use
>     
>     Now:
>       qemu-system-x86_64: -device ide-hd,drive=foo: Drive 'foo' is already in
>       use by another device
> 
> (We'll also produce message 1 in the oddball case where the user creates
> a drive if=something-not-handled-by-machine and then wires it up manually
> to two different devices; in this case their command line is doubly broken
> and if they use if=none as suggested by message 1 they'll then get message 2
> and can fix their own double-usage...)
> 
> Changes v1->v2:
>  * drop "warn if an if=<something> drive was also connected manually" patch
>  * change implementation of "improve error message" patch
> 
> 
> Peter Maydell (3):
>   qdev-properties-system: Change set_pointer's parse callback to use
>     Error
>   qdev-properties-system: Improve error message for drive assignment
>     conflict
>   hw/arm/virt: Make block devices default to virtio
> 
>  hw/arm/virt.c                    |  2 ++
>  hw/core/qdev-properties-system.c | 42 +++++++++++++++++++++++++++-------------
>  2 files changed, 31 insertions(+), 13 deletions(-)
> 
> -- 
> 1.9.1
> 
> 

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>