Re: [Qemu-block] [PATCH v2] raw-posix.c: Make physical devices usable in QEMU under Mac OS X host

[Stefan Hajnoczi]

On Fri, Jul 24, 2015 at 3:22 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Mon, Jul 20, 2015 at 5:17 PM, Programmingkid
> <address@hidden> wrote:
>>
>> On Jul 20, 2015, at 8:46 AM, Laurent Vivier wrote:
>>
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
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>>>
>>>
>>> On 20/07/2015 12:48, Stefan Hajnoczi wrote:
>>>> On Fri, Jul 17, 2015 at 03:24:34PM -0400, Programmingkid wrote:
>>>>>
>>>>> On Jul 17, 2015, at 9:41 AM, Stefan Hajnoczi wrote:
>>>>>
>>>>>> On Thu, Jul 16, 2015 at 04:46:07PM -0400, Programmingkid
>>>>>> wrote:
>>>>>>> @@ -2014,7 +2015,9 @@ kern_return_t GetBSDPath( io_iterator_t
>>>>>>> mediaIterator, char *bsdPath, CFIndex ma if (
>>>>>>> bsdPathAsCFString ) { size_t devPathLength; strcpy( bsdPath,
>>>>>>> _PATH_DEV ); -            strcat( bsdPath, "r" ); +
>>>>>>> if (flags & BDRV_O_NOCACHE) { +
>>>>>>> strcat(bsdPath, "r"); +            } devPathLength = strlen(
>>>>>>> bsdPath ); if ( CFStringGetCString( bsdPathAsCFString,
>>>>>>> bsdPath + devPathLength, maxPathSize - devPathLength,
>>>>>>> kCFStringEncodingASCII ) ) { kernResult = KERN_SUCCESS;
>>>>>>
>>>>>> Is this the fix that makes CD-ROM passthrough work for you?
>>>>>>
>>>>>> Does the guest boot successfully when you do:
>>>>>>
>>>>>> -drive if=ide,media=cdrom,cache=none,file=/dev/cdrom
>>>>>
>>>>> The guest fails during the boot process with the above command
>>>>> line.
>>>>
>>>> That means the issue you originally hit hasn't been solved yet.
>>>>
>>>> Take a look at s->needs_alignment and raw_probe_alignment().  In
>>>> the -drive cache=none case raw-posix needs to detect the correct
>>>> alignment (probably 2 KB for CD-ROMs).
>>>
>>> As raw_open_common() sets needs_alignment to true on BDRV_O_NOCACHE
>>> (cache="none") and raw_probe_alignment() detects alignment if
>>> needs_alignment is true, I don't understand why it doesn't work.
>>>
>>> Could you explain ?
>>
>>
>> I just did several tests with real CD-ROM discs and it does work. I first 
>> booted up Mac OS 10.2 with Stefan's command options using a professionally 
>> made CD, and it worked. I then did the same test again using a burned CD-R 
>> disc and it also worked. The last test I did was just listing the files from 
>> OpenBIOS using this: qemu-system-ppc -drive 
>> if=ide,media=cdrom,cache=none,file=/dev/cdrom. All tests were a success.
>>
>> Mac OS 10.2 panicked while booting in the original test using Stefan's 
>> command. I remember the panic happened about a minute into the boot process, 
>> so it could have been a guest issue rather than a QEMU issue. Either way 
>> everything is working now.
>
> I don't see what your patch changed to make -drive
> if=ide,media=cdrom,cache=none,file=/dev/cdrom work?

Sorry for the confusion, I understand now.

When you said the guest fails, I thought you meant that bdrv_read() is
still failing and the guest won't boot.  But you meant that the guest
kernel paniced (which is fine, not necessarily a CD-ROM problem).

Laurent's comment also clarifies that the BDRV_O_NOCACHE enables
probing, and therefore bdrv_read() will work correctly!

So I'm satisfied with why cache=none works now.

Thanks,
Stefan