[1/2] ISCSI: Set number of blocks to 0 for blank CDROM devices

The number of blocks of the device is used to compute the device size
in bdrv_getlength()/iscsi_getlength().
For MMC devices, the ReturnedLogicalBlockAddress in the READCAPACITY10
has a special meaning when it is 0.
In this case it does not mean that LBA 0 is the last accessible LBA,
and thus the device has 1 readable block, but instead it means that the
disc is blank and there are no readable blocks.

This change ensures that when the iSCSI LUN is loaded with a blank
DVD-R disk or similar that bdrv_getlength() will return the correct
size of the device as 0 bytes.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
---
 block/iscsi.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

Il 17/08/2012 04:36, Ronnie Sahlberg ha scritto:
> The number of blocks of the device is used to compute the device size
> in bdrv_getlength()/iscsi_getlength().
> For MMC devices, the ReturnedLogicalBlockAddress in the READCAPACITY10
> has a special meaning when it is 0.
> In this case it does not mean that LBA 0 is the last accessible LBA,
> and thus the device has 1 readable block, but instead it means that the
> disc is blank and there are no readable blocks.
> 
> This change ensures that when the iSCSI LUN is loaded with a blank
> DVD-R disk or similar that bdrv_getlength() will return the correct
> size of the device as 0 bytes.
> 
> Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
> ---
>  block/iscsi.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/block/iscsi.c b/block/iscsi.c
> index bb9cf82..fb420ea 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -717,7 +717,12 @@ iscsi_readcapacity10_cb(struct iscsi_context *iscsi, int status,
>      }
>  
>      itask->iscsilun->block_size = rc10->block_size;
> -    itask->iscsilun->num_blocks = rc10->lba + 1;
> +    if (rc10->lba == 0) {
> +        /* blank disk loaded */
> +        itask->iscsilun->num_blocks = 0;
> +    } else {
> +        itask->iscsilun->num_blocks = rc10->lba + 1;
> +    }
>      itask->bs->total_sectors    = itask->iscsilun->num_blocks *
>                                 itask->iscsilun->block_size / BDRV_SECTOR_SIZE ;
>  
> 

Thanks, applied to SCSI branch.  We'll see whether this hits 1.2.

Paolo

On Sun, Aug 19, 2012 at 7:57 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 17/08/2012 04:36, Ronnie Sahlberg ha scritto:
>> The number of blocks of the device is used to compute the device size
>> in bdrv_getlength()/iscsi_getlength().
>> For MMC devices, the ReturnedLogicalBlockAddress in the READCAPACITY10
>> has a special meaning when it is 0.
>> In this case it does not mean that LBA 0 is the last accessible LBA,
>> and thus the device has 1 readable block, but instead it means that the
>> disc is blank and there are no readable blocks.
>>
>> This change ensures that when the iSCSI LUN is loaded with a blank
>> DVD-R disk or similar that bdrv_getlength() will return the correct
>> size of the device as 0 bytes.
>>
>> Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
>> ---
>>  block/iscsi.c |    7 ++++++-
>>  1 files changed, 6 insertions(+), 1 deletions(-)
>>
>> diff --git a/block/iscsi.c b/block/iscsi.c
>> index bb9cf82..fb420ea 100644
>> --- a/block/iscsi.c
>> +++ b/block/iscsi.c
>> @@ -717,7 +717,12 @@ iscsi_readcapacity10_cb(struct iscsi_context *iscsi, int status,
>>      }
>>
>>      itask->iscsilun->block_size = rc10->block_size;
>> -    itask->iscsilun->num_blocks = rc10->lba + 1;
>> +    if (rc10->lba == 0) {
>> +        /* blank disk loaded */
>> +        itask->iscsilun->num_blocks = 0;
>> +    } else {
>> +        itask->iscsilun->num_blocks = rc10->lba + 1;
>> +    }
>>      itask->bs->total_sectors    = itask->iscsilun->num_blocks *
>>                                 itask->iscsilun->block_size / BDRV_SECTOR_SIZE ;
>>
>>
>
> Thanks, applied to SCSI branch.  We'll see whether this hits 1.2.

This patch only matters for the use case of having empty/blank media
loaded into an iscsi cdrom.
I doubt being able to "burn" data to an iscsi drive is very important or urgent,
so it is fine with me to delay until post 1.2

regards
ronnie sahlberg