Re: [Xen-devel] [RFC 02/23] xen/xenbus: client: Fix call of virt_to_mfn in xenbus_grant_ring

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi David,

On 19/05/15 14:51, David Vrabel wrote:
>> --- a/drivers/xen/xenbus/xenbus_client.c
>> +++ b/drivers/xen/xenbus/xenbus_client.c
>> @@ -379,16 +379,16 @@ int xenbus_grant_ring(struct xenbus_device *dev, void 
>> *vaddr,
>>      int i, j;
>>  
>>      for (i = 0; i < nr_pages; i++) {
>> -            unsigned long addr = (unsigned long)vaddr +
>> -                    (PAGE_SIZE * i);
>>              err = gnttab_grant_foreign_access(dev->otherend_id,
>> -                                              virt_to_mfn(addr), 0);
>> +                                              virt_to_mfn(vaddr), 0);
>>              if (err < 0) {
>>                      xenbus_dev_fatal(dev, err,
>>                                       "granting access to ring page");
>>                      goto fail;
>>              }
>>              grefs[i] = err;
>> +
>> +            vaddr = (char *)vaddr + PAGE_SIZE;
> 
> You don't need the cast here since vaddr is a void *.

Arithmetic on void pointer is a GCC extension [1]. I wasn't sure what is
the Linux policy on it.

Regards,

[1] https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer-Arith


-- 
Julien Grall

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