Re: [PATCH i-g-t 2/2] panthor: test dev_query buffer size variations

[Deborah Brouwer <deborah.brouwer@collabora.com>]

On Fri, Oct 16, 2026 at 10:06:54AM +0100, Liviu Dudau wrote:
> On Thu, Oct 15, 2026 at 04:44:58PM -0700, Deborah Brouwer wrote:
> > Add tests to check that the kernel driver will gracefully handle userspace
> > buffers that are smaller or larger than the kernel driver expected.
> > 
> > Also, add a test to ensure that the kernel driver is enforcing the
> > minimum buffer size and that the kernel driver will provide the size
> > when the userpointer is null.
> > 
> > This ensures UAPI compliance for DRM_IOCTL_PANTHOR_DEV_QUERY.
> > 
> > Signed-off-by: Deborah Brouwer <deborah.brouwer@collabora.com>
> > ---
> >  tests/panthor/panthor_query.c | 64 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 64 insertions(+)
> > 
> > diff --git a/tests/panthor/panthor_query.c b/tests/panthor/panthor_query.c
> > index afd58a5bd..8ff2e9652 100644
> > --- a/tests/panthor/panthor_query.c
> > +++ b/tests/panthor/panthor_query.c
> > @@ -7,6 +7,10 @@
> >  #include "panthor_drm.h"
> >  #include <stdint.h>
> >  
> > +#define GPU_INFO_MIN_SIZE \
> > +	(offsetof(struct drm_panthor_gpu_info, tiler_present) + \
> > +	 sizeof(((struct drm_panthor_gpu_info *)0)->tiler_present))
> > +
> >  int igt_main() {
> >  	int fd = -1;
> >  
> > @@ -20,10 +24,70 @@ int igt_main() {
> >  		struct drm_panthor_gpu_info gpu = {};
> >  
> >  		igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO, &gpu, sizeof(gpu), 0);
> > +		igt_assert_neq(gpu.gpu_id, 0);
> > +	}
> > +
> > +	igt_describe("Ensure kernel returns a GPU_INFO size.");
> > +	igt_subtest("query-size-null-pointer") {
> > +		uint32_t size;
> > +
> > +		size = igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO, NULL, 0, 0);
> > +
> > +		/*
> > +		 * The kernel returns its output structure size, which may be out
> > +		 * of sync with the header used to build these tests, so don't expect
> > +		 * that the sizes will match necessarily.
> > +		 */
> > +		igt_assert(size >= GPU_INFO_MIN_SIZE);
> > +	}
> > +
> > +	igt_describe("Ensure kernel enforces GPU_INFO minimum size.");
> > +	igt_subtest("query-size-too-small") {
> > +		struct drm_panthor_gpu_info gpu = {};
> > +
> > +		igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO,
> > +				  &gpu, GPU_INFO_MIN_SIZE - 1, EINVAL);
> > +	}
> > +
> > +	igt_describe("Ensure kernel accepts GPU_INFO minimum size.");
> > +	igt_subtest("query-min-size") {
> > +		struct drm_panthor_gpu_info gpu = {};
> > +
> > +		igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO,
> > +				  &gpu, GPU_INFO_MIN_SIZE, 0);
> 
> This last test feels redundant. We've checked that the kernel expects a struct of
> at least GPU_INFO_MIN_SIZE and we've checked that smaller sizes are rejected. If
> GPU_INFO_MIN_SIZE is rejected that means we are no longer supporting that size
> and user space should be upgraded, not necessarily that the kernel has a bug.

Ok, yes that makes sense, I'll drop this test in v2.
Thanks for reviewing this.

> 
> 
> Best regards,
> Liviu
> 
> >  
> >  		igt_assert_neq(gpu.gpu_id, 0);
> >  	}
> >  
> > +	igt_describe("Ensure kernel zeros out unused part of buffer.");
> > +	igt_subtest("query-too-big") {
> > +		uint32_t size;
> > +		size_t buf_size;
> > +		uint8_t *buf;
> > +
> > +		/*
> > +		 * Create a buffer that is larger than necessary.
> > +		 * Start with the size returned by the kernel in case it is out of
> > +		 * sync with these tests. Then add an extra 16 bytes and initialize
> > +		 * the entire buffer to non-zero values.
> > +		 */
> > +		size = igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO,
> > +					 NULL, 0, 0);
> > +		buf_size = (size_t)size + 16;
> > +		buf = malloc(buf_size);
> > +		igt_assert(buf);
> > +		memset(buf, 0xff, buf_size);
> > +
> > +		igt_panthor_query(fd, DRM_PANTHOR_DEV_QUERY_GPU_INFO,
> > +				  buf, buf_size, 0);
> > +
> > +		/* Check that the extra bytes were zeroed. */
> > +		for (size_t i = size; i < buf_size; i++)
> > +			igt_assert_eq(buf[i], 0);
> > +
> > +		free(buf);
> > +	}
> > +
> >  	igt_fixture() {
> >  		drm_close_driver(fd);
> >  	}
> > 
> > -- 
> > 2.56.0
> > 
> 
> -- 
> ====================
> | I would like to |
> | fix the world,  |
> | but they're not |
> | giving me the   |
>  \ source code!  /
>   ---------------
>     ¯\_(ツ)_/¯