Re: [Qemu-devel] [PATCHv3] Support default block interfaces per QEMUMachine

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> Christian Borntraeger <borntraeger@de.ibm.com> writes:
>
>> There are QEMUMachines that have neither IF_IDE nor IF_SCSI as a
>> default/standard interface to their block devices / drives. Therefore,
>> this patch introduces a new field default_block_type per QEMUMachine
>> struct. The prior use_scsi field becomes thereby obsolete and is
>> replaced through .default_block_type = IF_SCSI.
>>
>> This patch also changes the default for s390x to IF_VIRTIO and
>> removes an early hack that converts IF_IDE drives.
>
> Recommend to do this in a separate patch.
>
>> Other parties have already claimed interest (e.g. IF_SD for exynos)
>>
>> To create a sane default, for machines that dont specify a
>> default_block_type, this patch makes IF_IDE = 0 and IF_NONE = 1.
>> I checked all users of IF_NONE (blockdev.c and ww/device-hotplug.c)
>
> Typo: hw/
>
>> as well as IF_IDE and it seems that it is ok to change the defines -
>> in other words, I found no obvious (to me) assumption in the code
>> regarding IF_NONE==0.
>
> Checking for IF_NONE and IF_IDE is not enough; we have to check that
> BlockInterfaceType values are never used in a way that's broken by this
> change, such as C89 initializers and implicit comparisons to zero.
>
> I just did that, and couldn't find anything.

Almost missed this one: it changes this error message of monitor command
drive_add:

    (qemu) drive_add 0 if=ide
    Can't hot-add drive to type 1

to

    Can't hot-add drive to type 0

I don't think we care.  Yes, the error message sucks.

[...]