[SLOF] [PATCH] dev-null: The "read" function has to return 0 if nothing has been read

[Thomas Huth]

On 24.02.2016 09:38, Alexey Kardashevskiy wrote:
> On 02/24/2016 01:49 PM, David Gibson wrote:
>> On Wed, Feb 24, 2016 at 11:39:40AM +1100, Alexey Kardashevskiy wrote:
>>> On 02/24/2016 01:54 AM, Laurent Vivier wrote:
>>>>
>>>>
>>>> On 23/02/2016 15:40, Thomas Huth wrote:
>>>>> The "read" function of the dev-null device currently claims that
>>>>> the same amount of bytes has been read as input bytes have been
>>>>> requested. This causes grub to hang forever at the boot selection
>>>>> menu, since grub then thinks that there's a continuous stream of input
>>>>> data. If nothing has been read (which is always the case for the
>>>>> dev-null device), the "read" function should simply return 0 instead.
>>>>> Then grub also boots properly again after the typical short timeout.
>>>>>
>>>>> Reported-by: Laurent Vivier <lvivier at redhat.com>
>>>>> Signed-off-by: Thomas Huth <thuth at redhat.com>
>>>>
>>>> Tested-by: Laurent Vivier <lvivier at redhat.com>
>>>
>>> Thanks, applied.
>>>
>>> But how did you get this hang? How come that I've never seen that?
>>
>> I believe it happens when you try to boot without a console, or only a
>> console that SLOF doesn't understand like the virtio-console.
> 
> Oh. And how common is it to use virtio-console nowadays? Do I need to
> re-do the SLOF update for QEMU because of this?

I guess hardly anybody uses this (otherwise this bug would have been
noticed earlier) ... so IMHO no need to re-do the SLOF update now.
But anyway, some users might try this in the future, so we should maybe
have a virtio-console driver in SLOF one day...

 Thomas