Subject: [PATCH v7 6/9] ARM: miscellaneous vdso infrastructure, preparation

From: [email-masked] (Arnd Bergmann)
Date: Mon, 30 Jun 2014 12:11:43 +0200

On Monday 23 June 2014, Nathan Lynch wrote:
> +struct vdso_data {
> +       u32 seq_count;          /* sequence count - odd during updates */
> +       u16 use_syscall;        /* whether to fall back to syscalls */
> +       u16 cs_shift;           /* clocksource shift */
> +       u32 xtime_coarse_sec;   /* coarse time */
> +       u32 xtime_coarse_nsec;

Note that we will at some point have to introduce 64-bit time_t in user space
in some form. We will have to add new system calls for anything dealing with
time on the kernel boundary, but it would be good to be prepared here.

Is vdso_data an ABI-relevant data structure? If so, I think all you need here
is to make xtime_coarse_sec a u64 type for now, so we can add the other functions
later. The code can of course for now access only the lower half (keeping
endianess in mind), so there should not be any performance impact.

If the structure is not part of the ABI, there probably isn't much we can
do here.

	Arnd