Re: [Qemu-devel] [PATCH] block.c: fix real cdrom detection

[Laurent Vivier <lvivier@redhat.com>]

Hi,

On 29/06/2015 01:43, Programmingkid wrote:
> 
> On Jun 25, 2015, at 2:01 PM, Peter Maydell wrote:
> 
>> On 25 June 2015 at 18:56, Programmingkid
>> <programmingkidx@gmail.com> wrote:
>>> Nice to hear from you again Laurent. The only way a solution in 
>>> hdev_open() would work is if it could prevent
>>> find_image_format() from executing. Otherwise find_image_format()
>>> would just quit QEMU with an error.
>> 
>> The question you should be asking is "what is Linux doing for raw
>> CDROM devices that is different, such that it works there but
>> doesn't work on OSX?".
>> 
>> It would also be helpful to know which is the case that doesn't 
>> work. Does QEMU fail in all cases, or only if the cdrom drive is 
>> empty, or only if there's a disk in the drive?
> 
> QEMU fails if the cdrom is specified "-cdrom /dev/cdrom", and there
> is no cd in the drive.
> 
> QEMU also fails with a real cdrom in the drive.
> 
>> 
>> My initial suspicion is that we need OSX support in raw-posix.c for
>> handling the host CDROM specially -- note that Linux and FreeBSD
>> register a bdrv_host_cdrom with an is_inserted function.
> 
> The is_inserted function wouldn't make a difference.

In fact, if your patch fixes the problem, the is_inserted with no
cdrom should too:

with your " strcmp("/dev/cdrom", filename) == 0 ", you force the
selection of bdrv_raw (which is what to do).

without your patch, if "bdrv_is_inserted()" was implemented and no cdrom
in the drive " !bdrv_is_inserted(bs)  " should also select bdrv_raw.

It appears also that bdrv_host_cdrom is not registered in
bdrv_file_init(). I think this is the missing part to have a host cdrom
support on MacOS X.

Laurent