Re: [Qemu-devel] [PATCH v2] net/net: Change the default mac address of nic

[mike <qiudayu@linux.vnet.ibm.com>]

On 10/15/2013 02:05 PM, Stefan Weil wrote:
> Am 15.10.2013 07:57, schrieb mike:
>> On 10/15/2013 01:07 PM, Stefan Weil wrote:
>>> Am 15.10.2013 06:17, schrieb Mike Qiu:
>>>> Changelog to v1:
>>>>      Find remainder of macaddr->a[5] by modulo 256,
>>>>      otherwise it may be overflow by add index++.
>>>>
>>>> The default mac address is 52:54:00:12:34:56 + index, this will
>>>> cause problem that when we boot up more than one guest with all
>>>> mac addresses unset by default, assume that each guest has one
>>>> nic. In this situation, all the guest's nic has the same mac address.
>>>>
>>>> This patch is to solve this bug.
>>>>
>>>> Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
>>>> ---
>>>>    net/net.c | 9 ++++++---
>>>>    1 file changed, 6 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/net/net.c b/net/net.c
>>>> index c330c9a..9e72764 100644
>>>> --- a/net/net.c
>>>> +++ b/net/net.c
>>>> @@ -21,6 +21,8 @@
>>>>     * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>>>> DEALINGS IN
>>>>     * THE SOFTWARE.
>>>>     */
>>>> +#include <time.h>
>>>> +
>>>>    #include "config-host.h"
>>>>      #include "net/net.h"
>>>> @@ -147,12 +149,13 @@ void qemu_macaddr_default_if_unset(MACAddr
>>>> *macaddr)
>>>>          if (memcmp(macaddr, &zero, sizeof(zero)) != 0)
>>>>            return;
>>>> +    srand((unsigned)time(NULL));
>>>>        macaddr->a[0] = 0x52;
>>>>        macaddr->a[1] = 0x54;
>>>>        macaddr->a[2] = 0x00;
>>>> -    macaddr->a[3] = 0x12;
>>>> -    macaddr->a[4] = 0x34;
>>>> -    macaddr->a[5] = 0x56 + index++;
>>>> +    macaddr->a[3] = rand() % 256;
>>>> +    macaddr->a[4] = rand() % 256;
>>>> +    macaddr->a[5] = (rand() % 256 + index++) % 256;
>>>>    }
>>>>      /**
>>> There is no overflow which must be handled because a[5] is an uint8_t
>>> value, so the assignment automatically limits the range to 0...255.
>> OK, you are right, but I think we'd better to ensure this,
>> even though a[5] is an uint8_t.
>>> Is it reasonable to get a random mac address in your guest? I don't
>>> think so. It would no longer be possible to connect to a guest using
>>> ssh, restart that guest and connect again with ssh.
>> Why not? I have do the experiment, after reboot, the mac is not changed.
>> and the ip address always the same.
>>
>> And can be login to the guest after reboot.
> "restart" means terminate QEMU and start it again.
OK,  qemu support the mac address unset right ?
So it may be a joke if just can start only one VM with mac address unset :).

In your case, also can use monitor to get the mac address, simply 'info 
network' :)
Then you can do as if you set the mac address.

Thanks
Mike
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