Re: [Qemu-devel] [PATCH] Disable O_DIRECT for physical CDROM/DVD drives

[Anthony Liguori <anthony@codemonkey.ws>]

On 07/20/2010 11:45 AM, Natalia Portillo wrote:
> El 20/07/2010, a las 16:17, Jes.Sorensen@redhat.com escribió:
>
>    
>> From: Jes Sorensen<Jes.Sorensen@redhat.com>
>>
>> O_DIRECT (cache=none) requires sector alignment, however the physical
>> sector size of CDROM/DVD drives is 2048, as opposed to most disk
>> devices which use 512. QEMU is hard coding 512 all over the place, so
>> allowing O_DIRECT for CDROM/DVD devices does not work.
>>      
> What about if the device is a 4096 byte/sector hard disk, a 512 byte/sector CD-ROM (IRIX ones), a 2048 byte/sector magnetooptical?
>    

BlockDriverStates need to handle non-aligned reads/writes.  As I 
mentioned earlier, we need cdrom_pread/cdrom_pwrite functions that do 
RMWs as necessary.

Regards,

Anthony Liguori

> We should get rid of that hard codes and use real values.
>
>    
>> Signed-off-by: Jes Sorensen<Jes.Sorensen@redhat.com>
>> ---
>> block/raw-posix.c |    5 +++++
>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/block/raw-posix.c b/block/raw-posix.c
>> index 291699f..0ea79b6 100644
>> --- a/block/raw-posix.c
>> +++ b/block/raw-posix.c
>> @@ -1139,6 +1139,11 @@ static int cdrom_open(BlockDriverState *bs, const char *filename, int flags)
>>      BDRVRawState *s = bs->opaque;
>>
>>      s->type = FTYPE_CD;
>> +    if (flags&  BDRV_O_NOCACHE) {
>> +        fprintf(stderr, "Disabling unsupported O_DIRECT (cache=none) for "
>> +                "CDROM/DVD device (%s)\n", filename);
>> +        flags&= ~BDRV_O_NOCACHE;
>> +    }
>>
>>      /* open will not fail even if no CD is inserted, so add O_NONBLOCK */
>>      return raw_open_common(bs, filename, flags, O_NONBLOCK);
>> -- 
>> 1.7.1.1
>>
>>
>>      
>
>