Linus Torvalds wrote: > > On Thu, 2 Apr 2009, akpm@xxxxxxxxxxxxxxxxxxxx wrote: >> glibc entriely and use a syscall prototype which works without >> arch-specific wrappers inside the kernel: The offset argument is >> explicitly split into two 32bit values. > > Grr. That may make sense on 32-bit architectures, but makes no sense > what-so-ever on 64-bit ones. > > Why not just say that it's two "unsigned long" arguments, and split it by > "sizeof unsigned long". And then, on 64-bit architectures, the high bits > can be ignored. You can even get gcc to optimize it all away by doing > something like > > #define HALF_LONG (BITS_IN_LONG / 2) > > offset = (((loff_t)high << HALF_LONG) << HALF_LONG) | low; > > and then gcc should automaticaly notice that shifting up that way is just > a fancy way of saying "0", and ignore the high bits. > > How married are people to this crazy 2x "32 bits" model? The tricky corner case are 32bit compat syscalls on 64bit kernel, where a noticable number of archs (IIRC at least ppc, mips and s390) can't pass unaligned 64bit values through the syscall abi. The 32/32 split was done because of that. I think using two unsigned longs instead of two u32 should work. And allows us to handle 128bit file offsets on 64bit. That I'll call future-proof interface! Nevertheless I'd like to have comments from the arch maintainers on the idea. cheers, Gerd -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
