Re: [PATCH v3 3/5] tools/libs/foreignmemory: Fix PAGE_SIZE redefinition error

From: Costin Lupu <costin.lupu@cs.pub.ro>
To: Julien Grall <julien@xen.org>, xen-devel@lists.xenproject.org
Cc: Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH v3 3/5] tools/libs/foreignmemory: Fix PAGE_SIZE redefinition error
Date: Tue, 8 Jun 2021 15:37:23 +0300	[thread overview]
Message-ID: <153d38e4-b5fe-3530-138e-ad116a7c4c4c@cs.pub.ro> (raw)
In-Reply-To: <690806fb-e6e2-f61f-d7d6-a17efa6329d9@xen.org>

Hi Julien,

On 5/17/21 9:12 PM, Julien Grall wrote:
> Hi Costin,
> 
> On 10/05/2021 09:35, Costin Lupu wrote:
>> @@ -168,7 +168,7 @@ void
>> *osdep_xenforeignmemory_map(xenforeignmemory_handle *fmem,
>>       size_t i;
>>       int rc;
>>   -    addr = mmap(addr, num << PAGE_SHIFT, prot, flags | MAP_SHARED,
>> +    addr = mmap(addr, num << XC_PAGE_SHIFT, prot, flags | MAP_SHARED,
>>                   fd, 0);
>>       if ( addr == MAP_FAILED )
>>           return NULL;
>> @@ -198,9 +198,10 @@ void
>> *osdep_xenforeignmemory_map(xenforeignmemory_handle *fmem,
>>            */
>>           privcmd_mmapbatch_t ioctlx;
>>           xen_pfn_t *pfn;
>> -        unsigned int pfn_arr_size = ROUNDUP((num * sizeof(*pfn)),
>> PAGE_SHIFT);
>> +        unsigned int pfn_arr_size = ROUNDUP((num * sizeof(*pfn)),
>> XC_PAGE_SHIFT);
>> +        int os_page_size = getpagesize();
> 
> Hmmm... Sorry I only realized now that the manpage suggests that
> getpagesize() is legacy:
> 
>    SVr4, 4.4BSD, SUSv2.  In SUSv2 the getpagesize() call is labeled
> LEGACY, and in POSIX.1-2001 it has been dropped; HP-UX does not have
> this call.
> 
> And then:
> 
>   Portable applications should employ sysconf(_SC_PAGESIZE) instead of
> getpagesize():
> 
>           #include <unistd.h>
>           long sz = sysconf(_SC_PAGESIZE);
> 
> As this is only used by Linux, it is not clear to me whether this is
> important. Ian, what do you think?
> 

I think it would be safer to follow the man page indication. I've just
sent a v4.

>>   -        if ( pfn_arr_size <= PAGE_SIZE )
>> +        if ( pfn_arr_size <= os_page_size )
> 
> Your commit message suggests we are only s/PAGE_SHIFT/XC_PAGE_SHIFT/ but
> this is using getpagesize() instead. I agree it should be using the OS
> size. However, this should be clarified in the commit message.
> 

Done.

> The rest of the patch looks fine to me .

Thanks,
Costin