Re: [Qemu-devel] [PATCH 2/2] fdc: fix media detection

[Pavel Hrdina <phrdina@redhat.com>]

On 05/22/2012 03:42 PM, Kevin Wolf wrote:
> Am 22.05.2012 15:28, schrieb Pavel Hrdina:
>> On 05/22/2012 02:01 PM, Kevin Wolf wrote:
>>> Am 22.05.2012 12:59, schrieb Pavel Hrdina:
>>>> We have to set up 'media_changed' after guest start so floppy driver
>>>> could detect that there is no media in drive. For this purpose we call
>>>> 'fdctrl_change_cb' instead of 'fd_revalidate' in 'fdctrl_connect_drives'.
>>>> 'fd_revalidate' is called inside 'fdctrl_change_cb'.
>>>>
>>>> In 'fdctrl_handle_seek' we always set current track because we don't care
>>>> if there is media inserted or not.
>>>>
>>>> Signed-off-by: Pavel Hrdina<phrdina@redhat.com>
>>> Can you please add a qtest case that shows the problems that you're
>>> fixing in this series?
>> I'm new to qemu. By "add a qtest case" you mean update tests/fdc-test.c ?
> Sorry, I should have been more specific. Yes, that's what I mean.
>
>>>> diff --git a/hw/fdc.c b/hw/fdc.c
>>>> index cb4cd25..337b35a 100644
>>>> --- a/hw/fdc.c
>>>> +++ b/hw/fdc.c
>>>> @@ -1617,11 +1617,7 @@ static void fdctrl_handle_seek(FDCtrl *fdctrl, int direction)
>>>>        /* The seek command just sends step pulses to the drive and doesn't care if
>>>>         * there is a medium inserted of if it's banging the head against the drive.
>>>>         */
>>>> -    if (fdctrl->fifo[2]>   cur_drv->max_track) {
>>>> -        cur_drv->track = cur_drv->max_track;
>>>> -    } else {
>>>> -        cur_drv->track = fdctrl->fifo[2];
>>>> -    }
>>>> +    cur_drv->track = fdctrl->fifo[2];
>>> Why is it okay to have cur_drv->track point outside the floppy? Won't it
>>> mess up future calculations? Not all other places check it again
>>> cur_drv->max_track.
>>>
>>> Kevin
>> Well, you are right. Than we have to set 'max_track' even if there is no
>> media. I tested this on bare-metal without media and where floppy driver
>> ask to seek to specific track, it ends good and return specific track
>> position as actual.
>> I'll rewrite this behavior and send patch v2.
> You mean max_track = 0 isn't a good value to work with? How can a real
> drive position the head correctly when it doesn't have a media (and
> therefore doesn't know its geometry)?
>
> But if you have a good default value for max_track that we should use
> when no medium is present, go ahead.
>
> Kevin
When you try mount floppy in linux while there is no media then a floppy 
driver tries to seek on track 1. Virtual guest always get actual track 
position 0 so tries to seek again and stuck in loop which cause kernel 
panic. On bare-metal floppy driver gets actual track position 1 and stop 
seeking.

I thing, that a real drive ignore geometry and just seeks to specific 
position.

Pavel