Re: [Qemu-devel] [PATCH] block: vpc support for ~2 TB disks

[Paolo Bonzini]

Il 12/11/2012 20:12, Charles Arnold ha scritto:
> Ping?
> 
> Any thoughts on whether this is acceptable?

I would like to know what is done by other platforms.  Stefano, any idea
about XenServer?

Paolo

> - Charles
> 
>>>> On 10/30/2012 at 08:59 PM, in message <address@hidden>, Charles
> Arnold wrote: 
>> The VHD specification allows for up to a 2 TB disk size. The current
>> implementation in qemu emulates EIDE and ATA-2 hardware which only allows
>> for up to 127 GB.  This disk size limitation can be overridden by allowing
>> up to 255 heads instead of the normal 4 bit limitation of 16.  Doing so
>> allows disk images to be created of up to nearly 2 TB.  This change does
>> not violate the VHD format specification nor does it change how smaller
>> disks (ie, <=127GB) are defined. 
>>
>> Signed-off-by: Charles Arnold <address@hidden>
>>
>> diff --git a/block/vpc.c b/block/vpc.c
>> index b6bf52f..0c2eaf8 100644
>> --- a/block/vpc.c
>> +++ b/block/vpc.c
>> @@ -198,7 +198,8 @@ static int vpc_open(BlockDriverState *bs, int flags)
>>      bs->total_sectors = (int64_t)
>>          be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;
>>  
>> -    if (bs->total_sectors >= 65535 * 16 * 255) {
>> +    /* Allow a maximum disk size of approximately 2 TB */
>> +    if (bs->total_sectors >= 65535LL * 255 * 255) address@hidden
>>          err = -EFBIG;
>>          goto fail;
>>      }
>> @@ -524,19 +525,27 @@ static coroutine_fn int vpc_co_write(BlockDriverState 
>> *bs, int64_t sector_num,
>>   * Note that the geometry doesn't always exactly match total_sectors but
>>   * may round it down.
>>   *
>> - * Returns 0 on success, -EFBIG if the size is larger than 127 GB
>> + * Returns 0 on success, -EFBIG if the size is larger than ~2 TB. Override
>> + * the hardware EIDE and ATA-2 limit of 16 heads (max disk size of 127 GB)
>> + * and instead allow up to 255 heads.
>>   */
>>  static int calculate_geometry(int64_t total_sectors, uint16_t* cyls,
>>      uint8_t* heads, uint8_t* secs_per_cyl)
>>  {
>>      uint32_t cyls_times_heads;
>>  
>> -    if (total_sectors > 65535 * 16 * 255)
>> +    /* Allow a maximum disk size of approximately 2 TB */
>> +    if (total_sectors > 65535LL * 255 * 255) {
>>          return -EFBIG;
>> +    }
>>  
>>      if (total_sectors > 65535 * 16 * 63) {
>>          *secs_per_cyl = 255;
>> -        *heads = 16;
>> +        if (total_sectors > 65535 * 16 * 255) {
>> +            *heads = 255;
>> +        } else {
>> +            *heads = 16;
>> +        }
>>          cyls_times_heads = total_sectors / *secs_per_cyl;
>>      } else {
>>          *secs_per_cyl = 17;
> 
> 
> 
>