Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support

[Andy Lutomirski]

> On Sep 14, 2018, at 7:27 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> 
> On Fri, 14 Sep 2018, Andy Lutomirski wrote:
>>> On Sep 14, 2018, at 5:50 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>>> 
>>> With the storage array in place it's now trivial to support CLOCK_TAI in
>>> the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use
>>> of the fact that:
>>> 
>>> - CLOCK ids are set in stone
>>> - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so
>>>  the array slot 3 is unused
>>> - CLOCK_TAI is id 11 which results in 3 when masked with 0x3
>>> 
>>> Add the mask to the basetime array lookup and set up the CLOCK_TAI base
>>> time in update_vsyscall().
>> 
>> Thatâs... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere
>> to assert that this actually works?
> 
> Sure, but changing any of the clock ids will cause more wreckage than that.
> 

Iâm more concerned that we add a new one and break the magic masking. Maybe two start sharing the same slot. 

> Thanks,
> 
>    tglx