Re: [SUSPECTED SPAM][RESEND PATCH 1/2] tools/libxl: Mark pointer args of many functions constant

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/04/2021 18:12, Anthony PERARD wrote:
> On Fri, Dec 18, 2020 at 01:37:44PM -0800, Elliott Mitchell wrote:
>> --- a/tools/libs/light/libxl_internal.h
>> +++ b/tools/libs/light/libxl_internal.h
>> @@ -2073,9 +2073,9 @@ struct libxl__xen_console_reader {
>>  /* parse the string @s as a sequence of 6 colon separated bytes in to @mac 
>> */
>>  _hidden int libxl__parse_mac(const char *s, libxl_mac mac);
>>  /* compare mac address @a and @b. 0 if the same, -ve if a<b and +ve if a>b 
>> */
>> -_hidden int libxl__compare_macs(libxl_mac *a, libxl_mac *b);
>> +_hidden int libxl__compare_macs(const libxl_mac *a, const libxl_mac *b);
>>  /* return true if mac address is all zero (the default value) */
>> -_hidden int libxl__mac_is_default(libxl_mac *mac);
>> +_hidden int libxl__mac_is_default(const libxl_mac *mac);
> It turns out that older version of gcc complains about the const of
> libxl_mac:
>
>
>     libxl_nic.c: In function 'libxl_mac_to_device_nic':
>     libxl_nic.c:40:9: error: passing argument 1 of 'libxl__compare_macs' from 
> incompatible pointer type [-Werror]
>              if (!libxl__compare_macs(&mac_n, &nics[i].mac)) {
>              ^
>     In file included from libxl_nic.c:18:0:
>     libxl_internal.h:2076:13: note: expected 'const uint8_t (*)[6]' but 
> argument is of type 'uint8_t (*)[6]'
>      _hidden int libxl__compare_macs(const libxl_mac *a, const libxl_mac *b);
>                  ^
>     libxl_nic.c:40:9: error: passing argument 2 of 'libxl__compare_macs' from 
> incompatible pointer type [-Werror]
>              if (!libxl__compare_macs(&mac_n, &nics[i].mac)) {
>              ^
>     In file included from libxl_nic.c:18:0:
>     libxl_internal.h:2076:13: note: expected 'const uint8_t (*)[6]' but 
> argument is of type 'uint8_t (*)[6]'
>      _hidden int libxl__compare_macs(const libxl_mac *a, const libxl_mac *b);
>                  ^
>     libxl_nic.c: In function 'libxl__device_nic_setdefault':
>     libxl_nic.c:69:5: error: passing argument 1 of 'libxl__mac_is_default' 
> from incompatible pointer type [-Werror]
>          if (libxl__mac_is_default(&nic->mac)) {
>          ^
>     In file included from libxl_nic.c:18:0:
>     libxl_internal.h:2078:13: note: expected 'const uint8_t (*)[6]' but 
> argument is of type 'uint8_t (*)[6]'
>      _hidden int libxl__mac_is_default(const libxl_mac *mac);
>                  ^
>     cc1: all warnings being treated as errors

That's because the typedef for libxl_mac violates one of the well known
C beginner mistakes, by being a plain array behind the scenes.

A prototype of 'const libxl_mac mac[]' might fair better, except it
makes the code even more confusing to follow.

~Andrew