[PATCH v4 2/3] 32-bit ABIs: support stat syscall family

[Arnd Bergmann]

On Monday 29 August 2016, Yury Norov wrote:
> > 
> > We've gone back and forth on the arm64+ilp32 definition of the
> > existing stat64 , because that one cannot easily use the same
> > generic structure. I originally thought that using the 64-bit
> > layout of 'struct stat' was a good idea for arm64, but now
> > I don't see much of an advantage either way (the existing arm32
> > 'struct stat64' layout or the existing  arm64 'struct stat' layout).
> > 
> > Both of them are incompatible with the default layout for all
> > other new 32-bit architectures in user space, so pick one of the
> > two for the kernel interface, and convert it to the normal layout
> > in glibc using __xstat_conv():
> > 
> > - if you use the arm64 'struct stat' layout (as in the current
> >   kernel patches), you need a temporary buffer with the larger
> >   size and then copy over the time fields one by one
> > - if you instead use the arm32 'struct stat64' layout in the kernel,
> >   the size is the same, and the conversion is a one-line
> >   assignment of st_ino.
> > 
> >       Arnd
> 
> Ok. I'll do like this. I'd prefer 1st option, because 2nd implies
> allocating big buffer on kernel side.

On the kernel side, both require allocating a buffer, the second
one is just slightly bigger. The kernel uses its own internal
'struct kstat', which gets copied into one of the other structures.

	Arnd