KWin、libdrm、DRM从上到下全过程 —— drmModeAddFBxxx（27）

接前一篇文章：KWin、libdrm、DRM从上到下全过程 —— drmModeAddFBxxx（26）

上一回对于Linux Radix Tree知识进行了介绍和补强，本回将结合实际代码对于i915_gem_object_lookup_rcu函数及其所调用的idr_find函数的机制进行深入解析。

再次贴出i915_gem_object_lookup_rcu函数源码，在drivers/gpu/drm/i915/gem/i915_gem_object.h中，如下：

/**
 * i915_gem_object_lookup_rcu - look up a temporary GEM object from its handle
 * @filp: DRM file private date
 * @handle: userspace handle
 *
 * Returns:
 *
 * A pointer to the object named by the handle if such exists on @filp, NULL
 * otherwise. This object is only valid whilst under the RCU read lock, and
 * note carefully the object may be in the process of being destroyed.
 */
static inline s