[igt-dev] [i-g-t] lib/ioctl_wrappers: Keep IGT working without pread/pwrite ioctls

[Dixit, Ashutosh]

On Thu, 11 Mar 2021 12:47:41 -0800, Jason Ekstrand wrote:
> > diff --git a/lib/ioctl_wrappers.c b/lib/ioctl_wrappers.c
> > index 45415621b7..4440004c42 100644
> > --- a/lib/ioctl_wrappers.c
> > +++ b/lib/ioctl_wrappers.c
> > @@ -56,6 +56,7 @@
> >  #include "igt_debugfs.h"
> >  #include "igt_sysfs.h"
> >  #include "config.h"
> > +#include "i915/gem_mman.h"
> >
> >  #ifdef HAVE_VALGRIND
> >  #include <valgrind/valgrind.h>
> > @@ -324,6 +325,70 @@ void gem_close(int fd, uint32_t handle)
> >      do_ioctl(fd, DRM_IOCTL_GEM_CLOSE, &close_bo);
> >  }
> >
> > +static bool is_cache_coherent(int fd, uint32_t handle)
> > +{
> > +    return gem_get_caching(fd, handle) != I915_CACHING_NONE;
> > +}
> > +
> > +static void mmap_write(int fd, uint32_t handle, uint64_t offset,
> > +               const void *buf, uint64_t length)
> > +{
> > +    void *map = NULL;
> > +
> > +    if (!length)
> > +        return;
> > +
> > +    if (is_cache_coherent(fd, handle)) {
> > +        /* offset arg for mmap functions must be 0 */
> > +        map = __gem_mmap__cpu_coherent(fd, handle, 0, offset + length,
> > +                           PROT_READ | PROT_WRITE);
> > +        if (map)
> > +            gem_set_domain(fd, handle,
> > +                       I915_GEM_DOMAIN_CPU, I915_GEM_DOMAIN_CPU);
>
> Not sure how much it matters for IGT but the pread/pwrite ioctls
> appear to always leave the BO in the GTT domain.

It probably doesn't matter. This code here is actually copied from lib/intel_bufops.c:

https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/lib/intel_bufops.c#L423

Because it has been tested and verified to work and because it is already
used elsewhere my preference would be to leave as is unless you think
otherwise? Thanks.