On Wed May 2 2012 23:39:15 Sakari Ailus wrote: > Hi Hans, > > On Wed, May 02, 2012 at 10:45:22PM +0200, Hans Verkuil wrote: > > On Wed May 2 2012 21:13:47 Sakari Ailus wrote: > > > Replace enums in IOCTL structs by __u32. The size of enums is variable and > > > thus problematic. Compatibility structs having exactly the same as original > > > definition are provided for compatibility with old binaries with the > > > required conversion code. > > > > Does someone actually have hard proof that there really is a problem? You know, > > demonstrate it with actual example code? > > > > It's pretty horrible that you have to do all those conversions and that code > > will be with us for years to come. > > > > For most (if not all!) architectures sizeof(enum) == sizeof(u32), so there is > > no need for any compat code for those. > > Cases I know where this can go wrong are, but there may well be others: > > - ppc64: int is 64 bits there, and thus also enums, Are you really, really certain that's the case? If I look at arch/powerpc/include/asm/types.h it includes either asm-generic/int-l64.h or asm-generic/int-ll64.h and both of those headers define u32 as unsigned int. Also, if sizeof(int) != 4, then how would you define u32? Ask a ppc64 kernel maintainer what sizeof(int) and sizeof(enum) are in the kernel before we start doing lots of work for no reason. Looking at arch/*/include/asm/types.h it seems all architectures define sizeof(int) as 4. What sizeof(long) is will actually differ between architectures, but char, short and int seem to be fixed everywhere. Regards, Hans > > - Enums are quite a different concept in C++ than in C --- the compiler may > make assumpton based on the value range of the enums --- videodev2.h should > be included with extern "C" in that case, though, > > - C does not specify which integer type enums actually use; this is what GCC > manual says about it: > > <URL:http://www.gnu.org/software/gnu-c-manual/gnu-c-manual.html#Enumerations> > > So a compiler other than GCC should use 16-bit enums and conform to C > while breaking V4L2. This might be a theoretical issue, though. > > More discussion took place in this thread: > > <URL:http://www.spinics.net/lists/linux-media/msg46167.html> > > Regards, > > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
