[Qemu-devel] Re: [PATCH v2] QMP: Introduce the documentation for query-netdev and info netdev

[Miguel Di Ciurcio Filho]

On Mon, Jun 21, 2010 at 11:42 AM, Luiz Capitulino
<address@hidden> wrote:
>> +- "info": json-object containing the configuration information about the 
>> device.
>> +        - When "type" is "tap", the following values might be available:
>> +            - "fd": available if connected to an already opened TAP 
>> interface
>> +              (json-int, optional)
>> +            - "script": path to an script used to configure the interface, 
>> if
>> +              the value is "no" then no script is used. (json-string, only
>> +              present if "fd" is not present)
>
>  What if the script is called "no"? Better not to include the key in this 
> case.

Actually, it can't be named "no". Because if the name is "no", qemu
does not run any script. net/tap.c:net_tap_init():391 and
net/tap.c:net_init_tap:():462.

$ qemu -netdev type=tap,script=no,downscript=no....

But, returning "no" is really not a good idea, indeed. If scripts were
disabled in the command line, "script" and "downscript" should not
exist.

>> +            - "downscript": path to an script used to deconfigure the 
>> interface,
>> +              if the value is "no" then no script is used. (json-string, 
>> only
>> +              present if "fd" is not present)
>
>  Same as above.
>
>> +            - "ifname": name of the attached host interface (json-string, 
>> only
>> +              present if "fd" is not present)
>> +            - "vhost": vhost acceleration status, true if enabled, false
>> +              otherwise (json-boolean)
>> +            - "vnet_hdr": true if the IFF_VNET_HDR flag must be set, false
>> +              otherwise (json-boolean)
>
>  Why is vnet_hdr important?

Because of this (quoting the command line docs):

"use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag
use vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition"

So if "vnet_hdr" is true, it means that the VM is effectively using the feature.

>
>> +            - "vhostfd": positive number if the device is connected to an
>> +              already opened vhost net device, -1 otherwise (json-int)
>
>  Making the key option is better, IMO.
>

Indeed, same case as "script" and "downscript".

Regards,

Miguel