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authorChris Wilson <chris@chris-wilson.co.uk>2019-03-22 12:23:22 +0300
committerChris Wilson <chris@chris-wilson.co.uk>2019-03-22 16:12:30 +0300
commit9d1305ef80b95dde0337106ed8b826604e2155ad (patch)
tree8826f83b7b05432593b7296c73b80f974d438249 /drivers/gpu/drm/i915/i915_utils.h
parentb9d52d381e142fb3275430ac40ab119565d046f4 (diff)
downloadlinux-9d1305ef80b95dde0337106ed8b826604e2155ad.tar.xz
drm/i915: Introduce the i915_user_extension_method
An idea for extending uABI inspired by Vulkan's extension chains. Instead of expanding the data struct for each ioctl every time we need to add a new feature, define an extension chain instead. As we add optional interfaces to control the ioctl, we define a new extension struct that can be linked into the ioctl data only when required by the user. The key advantage being able to ignore large control structs for optional interfaces/extensions, while being able to process them in a consistent manner. In comparison to other extensible ioctls, the key difference is the use of a linked chain of extension structs vs an array of tagged pointers. For example, struct drm_amdgpu_cs_chunk { __u32 chunk_id; __u32 length_dw; __u64 chunk_data; }; struct drm_amdgpu_cs_in { __u32 ctx_id; __u32 bo_list_handle; __u32 num_chunks; __u32 _pad; __u64 chunks; }; allows userspace to pass in array of pointers to extension structs, but must therefore keep constructing that array along side the command stream. In dynamic situations like that, a linked list is preferred and does not similar from extra cache line misses as the extension structs themselves must still be loaded separate to the chunks array. v2: Apply the tail call optimisation directly to nip the worry of stack overflow in the bud. v3: Defend against recursion. v4: Fixup local types to match new uabi Opens: - do we include the result as an out-field in each chain? struct i915_user_extension { __u64 next_extension; __u64 name; __s32 result; __u32 mbz; /* reserved for future use */ }; * Undecided, so provision some room for future expansion. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190322092325.5883-1-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/gpu/drm/i915/i915_utils.h')
-rw-r--r--drivers/gpu/drm/i915/i915_utils.h31
1 files changed, 31 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index 9726df37c4c4..8baedcaddbba 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -105,6 +105,37 @@
__T; \
})
+/*
+ * container_of_user: Extract the superclass from a pointer to a member.
+ *
+ * Exactly like container_of() with the exception that it plays nicely
+ * with sparse for __user @ptr.
+ */
+#define container_of_user(ptr, type, member) ({ \
+ void __user *__mptr = (void __user *)(ptr); \
+ BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
+ !__same_type(*(ptr), void), \
+ "pointer type mismatch in container_of()"); \
+ ((type __user *)(__mptr - offsetof(type, member))); })
+
+/*
+ * check_user_mbz: Check that a user value exists and is zero
+ *
+ * Frequently in our uABI we reserve space for future extensions, and
+ * two ensure that userspace is prepared we enforce that space must
+ * be zero. (Then any future extension can safely assume a default value
+ * of 0.)
+ *
+ * check_user_mbz() combines checking that the user pointer is accessible
+ * and that the contained value is zero.
+ *
+ * Returns: -EFAULT if not accessible, -EINVAL if !zero, or 0 on success.
+ */
+#define check_user_mbz(U) ({ \
+ typeof(*(U)) mbz__; \
+ get_user(mbz__, (U)) ? -EFAULT : mbz__ ? -EINVAL : 0; \
+})
+
static inline u64 ptr_to_u64(const void *ptr)
{
return (uintptr_t)ptr;