Re: 32-bit time_t inside itimerval

[Lukasz Majewski <lukma@denx.de>]

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Hi Alistair,

> On Thu, Jan 2, 2020 at 4:28 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Thu, Jan 2, 2020 at 1:08 PM Lukasz Majewski <lukma@denx.de>
> > wrote:  
> > > > On Mon, Dec 30, 2019 at 10:22 PM Alistair Francis
> > > > <alistair23@gmail.com> wrote:  
> > > > > On Mon, Dec 30, 2019 at 12:11 PM Arnd Bergmann
> > > > > <arnd@arndb.de> wrote:  
> > > > I don't think it's
> > > > fundamentally different from the other system calls that he has
> > > > converted already to work with time64 callers.  
> > >
> > > I'm not aware of any RV32 specifics, but it seems to me that it
> > > would be appropriate to use the 64 bit version of struct
> > > __itimerspec64 in glibc - as for example in the conversion patch
> > > from [1].  
> >
> > What I mean is that rv32 otherwise does not convert between time32
> > and time64 interfaces because it always uses the time64 version,
> > so unlike the others, there is probably no helper to convert between
> > the timeval formats either.  
> 
> I have some patches prepared that will convert a 64-bit time_t to
> 32-bit for the required syscalls. It's generic for 32-bit archs, but
> will only apply when __TIMESIZE == 64.
> 
> I'll send an RFC out with the RV32 patches soon and then send patches
> when the 2.32 merge window opens up.

Great. Thanks :-)

> 
> 
> Alistair
> 
> >  
> > > As it was already mentioned - those calls set the time to be
> > > decremented and do not operate on "absolute" time values.
> > > Hence, I think that it would be good enough (for now?) to use 32
> > > bit API wrapped into 64 bit internal glibc values and just return
> > > errors when somebody wants to set timer relative expiration time
> > > to overflow time_t on 32 bit archs (arm,rv32).  
> >
> > Yes, that's the idea. The kernel already limits the range to 64-bit
> > nanoseconds because of its timer implementation, so truncating it
> > to 32-bit seconds does not change the behavior either.
> >  
> > > Arnd, am I correct that the struct itimerval to
> > > __kernel_old_itimerval conversion patch can be found here [2]?  
> >
> > Yes, that's right. This patch only changes the in-kernel
> > implementation as a step to removing the timeval definition from
> > the kernel's uapi headers, it does not change the behavior at all.
> >
> >        Arnd  




Best regards,

Lukasz Majewski

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