[ovs-dev] [PATCH v2] packet: proper return type for vlan_tci_to_pcp()

[Ben Pfaff]

On Thu, Feb 02, 2017 at 02:55:03PM -0800, Shu Shen wrote:
> On Tue, Jan 31, 2017 at 10:45:31AM -0800, Ben Pfaff wrote:
> > By my count, vlan_tci_to_pcp() is used in printf-like format
> > specifiers in 7 places in the tree.  Before this patch, it is used
> > with the following format specifiers:
> > 
> >         %d      3 times %x      1 time PRIu8   1 time PRIx8   1 time
> > 
> > Both %d and %x are obviously correct, portable format specifiers for
> > int, which is the return type of vlan_tci_to_pcp().  I contend that
> > PRIu8 and PRIx8 should be acceptable too because the integer
> > promotions convert uint8_t to int anyway.
> The problem is that PRIu8 and PRIx8 the specifiers are not promoted to
> 'u' and 'x' respectively on macOS.
> 
> For example, for PRIu*, on Mac OS, /usr/include/inttypes.h:
> 
>  #  define __PRI_8_LENGTH_MODIFIER__ "hh"
>  #  define __PRI_64_LENGTH_MODIFIER__ "ll"
>  #  define PRIu8         __PRI_8_LENGTH_MODIFIER__ "u"
>  #  define PRIu16        "hu"
>  #  define PRIu32        "lu"
>  #  define PRIu64        __PRI_64_LENGTH_MODIFIER__ "u"
> 
> While on Linux/glibc, /usr/include/inttypes.h:
> 
>  # define PRIu8          "u"
>  # define PRIu16         "u"
>  # define PRIu32         "u"
>  # define PRIu64         __PRI64_PREFIX "u"
> 
> where all PRIu* except PRIu64 are the same.
> 
> Therefore, using PRIu8 or PRIx8 with the int return type of
> vlan_tci_to_pcp() is causing compiler warnings on macOS.

What are the warnings?

There is no real problem with using %hhd or %hhu to print an int,
because printf() cannot tell the difference between an int and a char:
they are both passed as int.

> As PRIu8 and PRIx8 are indeed accurate specifier for pcp (Priority code
> point), the patch proposes changing the return type of
> vlan_tci_to_pcp().
> 
> In addition, the patch includes changes of format specifiers to
> consistently use PRI* specifier. But unfortunately as you pointed out
> below, there are two "%d" occurrences I missed. I'll put these specifier
> changes into a separate commit for clarity.

I don't see how putting them in a separate commit provides "clarity"
since the lack of the changes is most of my problem with the commit.