[igt-dev] [PATCH i-g-t v3] lib/i915/gem_mman: Add a helper for obtaining mappable aperture version

[Chris Wilson]

Quoting Janusz Krzysztofik (2019-05-31 09:53:41)
> Hi Chris,
> 
> On Friday, May 31, 2019 10:39:47 AM CEST Chris Wilson wrote:
> > Quoting Janusz Krzysztofik (2019-05-31 09:33:38)
> > > From: Janusz Krzysztofik <janusz.krzysztofik at intel.com>
> > > 
> > > If a test calls a function which depends on availabiblity of a
> > > supported mappable aperture, an error may be reported by the kernel on
> > > unsupported hardware.  That may negatively affect results reported by a
> > > test framework even if that test ignores the failure and succeedes.
> > > 
> > > This helper wraps an IOCTL call which returns a version number of a
> > > mappable aperture.  It may be used by tests which need to adjust their
> > > scope depending on availability of specific version of mappable
> > > aperture.
> > > 
> > > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at intel.com>
> > > Cc: Antonio Argenziano <antonio.argenziano at intel.com>
> > > Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> > > ---
> > > Changelog:
> > > v2 (internal) -> v3:
> > > - make the code less obsucre, more explicit (Antonio),
> > > - reword the helper documentation and commit message.
> > > 
> > > v1 (internal) -> v2 (internal):
> > > - minimize future potential conflicts with 
> > >   https://patchwork.freedesktop.org/patch/294053/?series=58551&rev=1
> > >   (no progress with than one so not waiting for it any longer):
> > >   - convert the helper to a drop-in replacement of the one from the
> > >     above mentioned patch, returning mappable aperture version, not
> > >     only information on its availability,
> > >   - drop any other wrappers,
> > > - document the helper,
> > > - reword commit message.
> > > 
> > >  lib/i915/gem_mman.c | 22 ++++++++++++++++++++++
> > >  lib/i915/gem_mman.h |  1 +
> > >  2 files changed, 23 insertions(+)
> > > 
> > > diff --git a/lib/i915/gem_mman.c b/lib/i915/gem_mman.c
> > > index 3cf9a6bb..3a3f3e5c 100644
> > > --- a/lib/i915/gem_mman.c
> > > +++ b/lib/i915/gem_mman.c
> > > @@ -40,6 +40,28 @@
> > >  #define VG(x) do {} while (0)
> > >  #endif
> > >  
> > > +/**
> > > + * gem_mmap__gtt_version:
> > > + * @fd: open i915 drm file descriptor
> > > + *
> > > + * This functions wraps up an IOCTL to obtain mappable aperture version.
> > > + *
> > > + * Returns: mappable aperture version, -1 on failure.
> > > + */
> > > +int gem_mmap__gtt_version(int fd)
> > > +{
> > > +       int gtt_version, ret;
> > > +       struct drm_i915_getparam gp = {
> > > +               .param = I915_PARAM_MMAP_GTT_VERSION,
> > > +               .value = &gtt_version,
> > > +       };
> > > +
> > > +       ret = ioctl(fd, DRM_IOCTL_I915_GETPARAM, &gp);
> > > +       if (ret == 0)
> > > +               ret = gtt_version;
> > > +       return ret;
> > 
> > Maybe the actual error returned by the kernel and not glibc would be
> > interesting in the future?
> 
> errno is not overwritten by the helper so it is available to IGT after it is 
> called and actually reported when a call to the helper is wrapped with 
> igt_require().  Do we need more?

Yes, we typically return the error and do not use errno. Imagine if we
just replaced ioctl() with syscall() :)
-Chris