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

[Programmingkid]

On Jun 23, 2015, at 2:06 PM, John Snow wrote:

> 
> 
> On 06/23/2015 01:56 PM, Programmingkid wrote:
>> Fix real cdrom detection so that a real cdrom can actually be used.
>> 
>> signed-off-by: John Arbuckle <address@hidden
>> <mailto:address@hidden>>
>> 
>> This patch has been tested on Mac OS X host and guest. 
>> Command used: qemu-system-ppc -cdrom /dev/cdrom
>> 
>> Note: I was able to view the files using OpenBIOS, but not on 
>> Mac OS X. The size of the disc is reported correctly but some
>> error happens that prevents it from mounting in Mac OS X. This
>> is probably another bug with QEMU.
>> 
>> ---
>> block.c |    3 ++-
>> 1 files changed, 2 insertions(+), 1 deletions(-)
>> 
>> diff --git a/block.c b/block.c
>> index dd4f58d..75ccfad 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -583,7 +583,8 @@ static int find_image_format(BlockDriverState *bs,
>> const char *filename,
>>     int ret = 0;
>> 
>> 
>> 
>>     /* Return the raw BlockDriver * to scsi-generic devices or empty
>> drives */
>> -    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {
>> +    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0 
>> +               || strcmp("/dev/cdrom", filename) == 0) {
>>         *pdrv = &bdrv_raw;
>>         return ret;
>>     }
>> -- 
>> 1.7.5.4
>> 
> 
> So what's the issue that this patch attempts to fix and how did you
> determine that the fix was needed here? It doesn't look like it respects
> proper abstraction at a glance.

Without the patch, QEMU would just quit when the "-cdrom /dev/cdrom" option is 
given.

Before the patch, the bdrv_open_inherit() function would be incorrectly called. 
Its documentation says "Opens a disk image (raw, qcow2, vmdk, ...)" meaning 
only for disk image files (not for real media). This patch prevents the 
bdrv_open_inherit() function from ever being called. It sets the pdrv variable 
to the raw format. This made sense to me since a real cdrom is read in the raw 
format.

A quick test does show the patch works. A real cdrom is successfully opened on 
qemu-system-i386 using a Windows XP guest.