> On Oct 1, 2015, at 2:29 PM, Arnd Bergmann <a...@arndb.de> wrote: > >> On Thursday 01 October 2015 22:15:20 Yury Norov wrote: >> >> Regarding time_t, it, of course, doesn't takes much time to make it >> 32-bit, but I think 64 bit is better because of Y2038. X32 and mips >> n32 has time_t 64-bit (and ppc, not sure), and that's OK for them. > > I'm pretty sure that n32 has 32-bit time_t, and we know that it still > causes real-world problems on x32: socket timestamps, v4l, alsa and > other subsystems all have bugs in this area that are hard to fix. > >> That's OK for BSD as well. The objection may come from users of ABI, >> complaining portability problems, but I found no such complains in >> public discussions. >> >> Nevertheless, as I told, I do not see any problem to rework time_t. >> But some arguments supporting this decision are appreciated. >> >> The downside of 32 bit time_t is that we still face Y2038 problem, >> but that's the other story fixing it. > > The main reason for 32-bit time_t is compatibility with existing > ioctls (also getsockopts and some others), and having a sane way > for fixing them. We cannot change compat_time_t to be 64-bit > without breaking arm32 compat mode, and we can't use the native > 64-bit ioctl implementation on ARM64/ILP32 because that breaks > all interfaces that pass 'long' or a pointer. > > This means drivers that currently pass a time_t (or timeval, timespec > etc) need to not only have a compat_ioctl handler to convert it, > they also need to check whether which of the two compat modes they > are talking to. This is a mess to add (I know, because I'm working > on this for y2038 compliance for normal 32-bit mode), and making > the two behave differently makes it even harder to get right for > all cases. > >> __kernel_long_t is the same. Now it's 64 bits length. Compatibility >> may suffer, but, again, there're no complains, and in long run it >> looks better. > > __kernel_long_t isn't actually used that much, and rarely used in > places where it matters. The idea was to be able to reuse the > native syscalls rather than the compat syscall calls, but that > comes with the downside of defining the ABI in a way that is > incompatible with all other 32-bit user space. > > Having a 64-bit __kernel_off_t is similar to the 64-bit time_t: > a good idea in principle, but it breaks device drivers that > expect user space to pass 32-bit arguments. For any interface > that really needs 64-bit data, we have to fix it for all > 32-bit architectures, and we're better off avoiding special > cases.
Ok, we will rewrite these patches using 32bit time_t and 32bit off_t and redo the toolchain support for them. Note this is going back to the abi I had originally done when I submitted my original version when it was asked to change time_t to be 64bit. Thanks, Andrew > > Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
