Re: [Qemu-devel] Re: [PATCH RFC] virtio: add features qdev property

[Markus Armbruster]

Gerd Hoffmann <address@hidden> writes:

> On 12/14/09 12:10, Michael S. Tsirkin wrote:
>> On Mon, Dec 14, 2009 at 11:24:41AM +0100, Gerd Hoffmann wrote:
>> for block:
>>      if (strcmp(s->serial_str, "0"))
>>          features |= 1<<  VIRTIO_BLK_F_IDENTIFY;
>>
>>      if (bdrv_is_read_only(s->bs))
>>          features |= 1<<  VIRTIO_BLK_F_RO;
>
> Sure you want these be configurable?
>
>> Also, I'd like these things to be saved in bits and not add a ton
>> of fields in device. Ideas how to do this?
>
> I guess you only want disable features?
>
> You could have a bitmap property then, which accepts names for the
> bits. It would need a table like this ...
>
>    char *bitnames[] = {
>       [ VIRTIO_BLK_F_IDENTIFY ] = "blk-identify",
>       [ VIRTIO_BLK_F_RO       [ = "blk-ro",
>       [ ... ]
>    };
>
> Then the property parser would accepts strings such as 'bit1|bit2' and
> you can have
>
>   -device 'virtio-blk-pci,disable=blk-identify|ring-indirect'
>
> The driver will just do 'vdev->host_features &= ~disable'.

Use of '|' in option argument syntax is user-hostile, because it
requires quoting in the shell.  What about '+'?