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_...
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