Re: [Qemu-devel] [PATCH] raw-posix.c: remove raw device access for cdrom

[Laurent Vivier <lvivier@redhat.com>]

On 02/07/2015 09:18, Paolo Bonzini wrote:
> 
> 
> On 02/07/2015 00:13, Programmingkid wrote:
>> Fix real cdrom access in Mac OS X so it can be used in QEMU.
>> It simply removes the r from a device file's name. This
>> allows for a real cdrom to be accessible to the guest.
>> It has been successfully tested with a Windows XP guest
>> in qemu-system-i386. The qemu-system-ppc emulator doesn't
>> quit anymore, but there is another problem that prevents a 
>> real cdrom from working.
>>
>> Signed-off-by: John Arbuckle <programmingkidx@gmail.com
>> <mailto:programmingkidx@gmail.com>>
>>
>> ---
>>  block/raw-posix.c |   10 ++++++++++
>>  1 files changed, 10 insertions(+), 0 deletions(-)
>>
>> diff --git a/block/raw-posix.c b/block/raw-posix.c
>> index a967464..3585ed9 100644
>> --- a/block/raw-posix.c
>> +++ b/block/raw-posix.c
>> @@ -2096,6 +2096,16 @@ static int hdev_open(BlockDriverState *bs, QDict
>> *options, int flags,
>>          kernResult = FindEjectableCDMedia( &mediaIterator );
>>          kernResult = GetBSDPath( mediaIterator, bsdPath, sizeof(
>> bsdPath ) );
>>
>>  
>>
>> +        /*
>> +         * Remove the r from cdrom block device if needed.
>> +         * /dev/rdisk1 would become /dev/disk1.
>> +         * The r means raw access. It doesn't work well.
>> +         */
>> +        int sizeOfString = strlen("/dev/r");
>> +        if (strncmp("/dev/r", bsdPath, sizeOfString) == 0) {
>> +            sprintf(bsdPath, "/dev/%s", bsdPath + sizeOfString);
>> +        }
> 
> I think you can just remove the strcat in here:
> 
>         if ( bsdPathAsCFString ) {
>             size_t devPathLength;
>             strcpy( bsdPath, _PATH_DEV );
>             strcat( bsdPath, "r" );
>             devPathLength = strlen( bsdPath );
>             if ( CFStringGetCString( bsdPathAsCFString, bsdPath +
> devPathLength, maxPathSize - devPathLength, kCFStringEncodingASCII ) ) {
>                 kernResult = KERN_SUCCESS;
>             }
>             CFRelease( bsdPathAsCFString );
> 
> So it's still a one-line change.  What are the other consequences of
> removing the "r"?

This code seems to be a cut'n'paste of an Apple example (bad...):

https://developer.apple.com/library/mac/samplecode/CDROMSample/Listings/CDROMSample_CDROMSample_c.html

Without this interesting comment:

    Add "r" before the BSD node name from the I/O Registry to specify
    the raw disknode. The raw disk nodes receive I/O requests directly
    and do not go through the buffer cache.

Laurent