On Wed, 22 Apr 2015, Arnd Bergmann wrote: > On Wednesday 22 April 2015 10:45:23 Thomas Gleixner wrote: > > On Tue, 21 Apr 2015, Thomas Gleixner wrote: > > > So we could save one translation step if we implement new syscalls > > which have a scalar nsec interface instead of the timespec/timeval > > cruft and let user space do the translation to whatever it wants. > > > > So > > > > sys_clock_nanosleep(const clockid_t which_clock, int flags, > > const struct timespec __user *expires, > > struct timespec __user *reminder) > > > > would get the new syscall variant: > > > > sys_clock_nanosleep_ns(const clockid_t which_clock, int flags, > > const s64 expires, s64 __user *reminder) > > As you might expect, there are a number of complications with this > approach: > > - John Stultz likes to point out that it's easier to do one change > at a time, so extending the interface to 64-bit has less potential > of breaking things than a more fundamental change. I think it's > useful to drop a lot of the syscalls when a more modern version > is around (e.g. let libc implement usleep and nanosleep through > clock_nanosleep), but keep the syscalls as close to the known-working > 64-bit versions as we can. Well. I don't see a massive risk when implementing e.g. usleep/nanosleep & al with clock_nanosleep_ns(). > - The inode timestamp related syscalls (stat, utimes and variants > thereof) require the full range of time64_t and cannot use ktime_t. I'm aware that there are a lot of interfaces which cannot use ktime_t. That's fine. > - converting between timespec types of different size is cheap, > converting timespec to ktime_t is still relatively cheap, but > converting ktime_t to timespec is rather expensive (at least eight > 32-bit multiplies, plus a few shifts and additions if you don't > have 64-bit arithmetic). Right. That's what I said vs. gettime(). > - ioctls that pass a timespec need to keep doing that or would require > a source-level change in user space instead of recompiling. No argument here. > We should probably look at it separately for each syscall. It's > quite possible that we find a number of them for which it helps > and others for which it hurts, so we need to see the big pictures. Agreed. > There are also a few other calls that will never need 64-bit > time_t because the range is limited by the need to only ever > pass relative timeouts (select, poll, io_getevents, recvmmsg, > clock_getres, rt_sigtimedwait, sched_rr_get_interval, getrusage, > waitid, semtimedop, sysinfo), so we could actually leave them > using a 32-bit structure and have the libc do the conversion. Indeed. > I've started a list of affected syscalls at > https://docs.google.com/spreadsheets/d/1HCYwHXxs48TsTb6IGUduNjQnmfRvMPzCN6T_0YiQwis/edit?usp=sharing > > Still adding more calls and description, let me know if you want edit > permissions. Only if you have a strong backup system for this file. My GUI foo is rather limited :) Thanks, tglx -- 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
