Re: [PATCH] io_uring: use __kernel_timespec in timeout ABI

* Arnd Bergmann:

On Tue, Oct 1, 2019 at 5:38 PM Jens Axboe [off-list ref] wrote:

quoted

On 10/1/19 8:09 AM, Jens Axboe wrote:

quoted

On 9/30/19 2:20 PM, Arnd Bergmann wrote:

quoted

All system calls use struct __kernel_timespec instead of the old struct
timespec, but this one was just added with the old-style ABI. Change it
now to enforce the use of __kernel_timespec, avoiding ABI confusion and
the need for compat handlers on 32-bit architectures.

Any user space caller will have to use __kernel_timespec now, but this
is unambiguous and works for any C library regardless of the time_t
definition. A nicer way to specify the timeout would have been a less
ambiguous 64-bit nanosecond value, but I suppose it's too late now to
change that as this would impact both 32-bit and 64-bit users.

Thanks for catching that, Arnd. Applied.

On second thought - since there appears to be no good 64-bit timespec
available to userspace, the alternative here is including on in liburing.

What's wrong with using __kernel_timespec? Just the name?
I suppose liburing could add a macro to give it a different name
for its users.

Yes, mostly the name.

__ names are reserved for the C/C++ implementation (which does not
include the kernel).  __kernel_timespec looks like an internal kernel
type to the uninitiated, not a UAPI type.

Once we have struct timespec64 in userspace, you also end up with
copying stuff around or introducing aliasing violations.

I'm not saying those concerns are valid, but you asked what's wrong with
it. 8-)

Thanks,
Florian