[PATCH] v4l2: unset _TIME_BITS in addition to _FILE_OFFSET_BITS

[Kieran Bingham]

Quoting Steve Langasek (2024-03-22 22:52:54)
> On Thu, Mar 21, 2024 at 09:21:19AM +0000, Kieran Bingham wrote:
> > Hi Steve, Dylan,
> 
> > Quoting Dylan A�ssi (2024-03-20 16:58:40)
> > > From: Steve Langasek <steve.langasek at canonical.com>
> 
> > > libcamera fails to build from source in Debian/Ubuntu on 32-bit
> > > architectures under 64-bit time_t (to avoid the 'year 2038
> > > problem'), because its v4l2 module legitimately un-sets
> > > _FILE_OFFSET_BITS for building but this is not allowed without
> > > also unsetting _TIME_BITS.
> 
> > > Having verified that nothing in this module is sensitive to 64-bit
> > > time_t (none of the functions it intercepts handle time), we also
> > > unset _TIME_BITS to allow this to build as before.
> 
> > Should we be setting -D_TIME_BITS=32 or anything like that, in the same
> > way that immediately after unsetting _FILE_OFFSET_BITS we set that to
> > 32?
> 
> No, there's no need to set it to another value.  The default behavior is for
> it to be unset.  If some libc implementation other than glibc wants to set
> it to a value other than 64, that's the business of that implementation.
> 
> I don't know why you're setting -D_FILE_OFFSET_BITS=32 either fwiw and think
> this is probably wrong, but I was going for a minimal fix here for the
> TIME/FILE bits incompatibility.

I would suspect it's because we're implementing a kernel interface in
userspace, and we only implement a single version (32 bit). But that's
speculation - and probably Paul would know more.

 Cc: Paul

 
> > > Signed-off-by: Steve Langasek <steve.langasek at canonical.com>
> > > Reviewed-by: Dylan A�ssi <dylan.aissi at collabora.com>

Well, if you're sure the default is sufficient, I don't object to adding
this flag so:


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> > > ---
> > >  src/v4l2/meson.build | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/src/v4l2/meson.build b/src/v4l2/meson.build
> > > index e88e0b33..12d1e2a4 100644
> > > --- a/src/v4l2/meson.build
> > > +++ b/src/v4l2/meson.build
> > > @@ -23,6 +23,7 @@ v4l2_compat_cpp_args = [
> > >      # file operations, disable transparent large file support.
> > >      '-U_FILE_OFFSET_BITS',
> > >      '-D_FILE_OFFSET_BITS=32',
> > > +    '-U_TIME_BITS',
> > >      '-D_LARGEFILE64_SOURCE',
> > >      '-fvisibility=hidden',
> > >  ]
> > > -- 
> > > 2.30.2
> > >
> > 
> 
> Cheers,
> -- 
> Steve Langasek                   Give me a lever long enough and a Free OS
> Debian Developer                   to set it on, and I can move the world.
> Ubuntu Developer                                   https://www.debian.org/
> slangasek at ubuntu.com                                     vorlon at debian.org