Mesa初始化流程重学习之eglInitialize

引言

说来也惭愧，Mesa搞了这么久了，每次都想深入下，可是每次都是浅尝辄止了。这次趁着有了一定的闲暇时间并且有了调试景嘉微显卡的机会，还是想重新学习下，深入研究下！不说达到某个程度吗，至少能充实点！

这里我使用的mesa版本是22.3.7！其它版本可能存在一定差异，应该不大！

tree src/  -L 1
src/
├── amd
├── android_stub
├── asahi
├── broadcom
├── c11
├── compiler
├── drm-shim
├── egl
├── etnaviv
├── freedreno
├── gallium
├── gbm
├── getopt
├── glx
├── gtest
├── hgl
├── imagination
├── imgui
├── intel
├── loader
├── mapi
├── mesa
├── meson.build
├── microsoft
├── nouveau
├── panfrost
├── tool
├── util
├── virtio
└── vulkan

29 directories, 1 file



tree src/gallium/  -L 2
src/gallium/
├── auxiliary
│   ├── cso_cache
│   ├── draw
│   ├── driver_ddebug
│   ├── driver_noop
│   ├── driver_trace
│   ├── gallivm
│   ├── hud
│   ├── indices
│   ├── meson.build
│   ├── nir
│   ├── os
│   ├── pipebuffer
│   ├── pipe-loader
│   ├── postprocess
│   ├── renderonly
│   ├── rtasm
│   ├── target-helpers
│   ├── tessellator
│   ├── tgsi
│   ├── translate
│   ├── util
│   └── vl
├── drivers
│   ├── asahi
│   ├── crocus
│   ├── d3d12
│   ├── etnaviv
│   ├── freedreno
│   ├── i915
│   ├── iris
│   ├── lima
│   ├── llvmpipe
│   ├── xxx_gpu
│   ├── nouveau
│   ├── panfrost
│   ├── r300
│   ├── r600
│   ├── radeonsi
│   ├── softpipe
│   ├── svga
│   ├── tegra
│   ├── v3d
│   ├── vc4
│   ├── virgl
│   └── zink
├── frontends
│   ├── clover
│   ├── d3d10umd
│   ├── dri
│   ├── glx
│   ├── hgl
│   ├── lavapipe
│   ├── nine
│   ├── omx
│   ├── osmesa
│   ├── rusticl
│   ├── va
│   ├── vdpau
│   ├── wgl
│   └── xa
├── include
│   ├── frontend
│   ├── pipe
│   └── winsys
├── meson.build
├── README.portability
├── targets
│   ├── d3d10sw
│   ├── d3dadapter9
│   ├── dri
│   ├── dri-vdpau.dyn
│   ├── haiku-softpipe
│   ├── lavapipe
│   ├── libgl-gdi
│   ├── libgl-xlib
│   ├── omx
│   ├── opencl
│   ├── osmesa
│   ├── pipe-loader
│   ├── rusticl
│   ├── va
│   ├── vdpau
│   ├── wgl
│   └── xa
├── tests
│   ├── meson.build
│   ├── python
│   ├── trivial
│   └── unit
├── tools
│   ├── addr2line.sh
│   └── trace
└── winsys
    ├── amdgpu
    ├── asahi
    ├── crocus
    ├── d3d12
    ├── etnaviv
    ├── freedreno
    ├── i915
    ├── iris
    ├── kmsro
    ├── lima
    ├── xxx_gpu
    ├── nouveau
    ├── panfrost
    ├── radeon
    ├── svga
    ├── sw
    ├── tegra
    ├── v3d
    ├── vc4
    └── virgl

108 directories, 6 files

一. 核心结构体和关系

_EGLDisplay和dri2_egl_display之间的关系

typedef struct _egl_display _EGLDisplay;

struct _egl_display
{
    ...
   _EGLPlatformType Platform; /**< The type of the platform display */
   void *PlatformDisplay;     /**< A pointer to the platform display */

   _EGLDevice *Device;        //这里的Driver指向_eglDriver，实现在Egl_dri2.c
   const _EGLDriver *Driver;  /**< Matched driver of the display */    
   ...
   /* these fields are set by the driver during init */
   void *DriverData;          /**< Driver private data */指向dri2_egl_display
   //disp->DriverData = (void *) dri2_dpy;
   _EGLExtensions Extensions; /**< Extensions supported */   
    ...
}



struct dri2_egl_display
{
   const struct dri2_egl_display_vtbl *vtbl;

   mtx_t lock;

   int dri2_major;
   int dri2_minor;
   __DRIscreen *dri_screen; //这个screen很重要
   bool own_dri_screen;
   const __DRIconfig **driver_configs;
   void *driver;
   const __DRIcoreExtension *core;  //这些会在初始化的时候被赋值，指向target的dri前端
   const __DRIimageDriverExtension *image_driver;
   const __DRIdri2Extension *dri2;
   const __DRIswrastExtension *swrast;
   const __DRIkopperExtension *kopper;
   const __DRI2flushExtension *flush;
   const __DRI2flushControlExtension *flush_control;
   const __DRItexBufferExtension *tex_buffer;
   const __DRIimageExtension *image;
   const __DRIrobustnessExtension *robustness;
   const __DRI2configQueryExtension *config;
   const __DRI2fenceExtension *fence;
   const __DRI2bufferDamageExtension *buffer_damage;
   const __DRI2blobExtension *blob;
   const __DRI2rendererQueryExtension *rendererQuery;
   const __DRI2interopExtension *interop;
   const __DRIconfigOptionsExtension *configOptions;
   const __DRImutableRenderBufferDriverExtension *mutable_render_buffer;
   int fd;

   /* dri2_initialize/dri2_terminate increment/decrement this count, so does
    * dri2_make_current (tracks if there are active contexts/surfaces). */
   int ref_count;

   bool own_device;
   bool invalidate_available;
   int min_swap_interval;
   int max_swap_interval;
   int default_swap_interval;
#ifdef HAVE_DRM_PLATFORM
   struct gbm_dri_device *gbm_dri;
#endif

   char *driver_name;

   const __DRIextension **loader_extensions;
   const __DRIextension **driver_extensions;

#ifdef HAVE_X11_PLATFORM
   xcb_connection_t *conn;
   xcb_screen_t *screen;
   bool swap_available;
#ifdef HAVE_DRI3
   bool multibuffers_available;
   int dri3_major_version;
   int dri3_minor_version;
   int present_major_version;
   int present_minor_version;
   struct loader_dri3_extensions loader_dri3_ext;
   struct loader_dri3_screen_resources screen_resources;
#endif
#endif

#ifdef HAVE_WAYLAND_PLATFORM
   struct wl_display *wl_dpy;
   struct wl_display *wl_dpy_wrapper;
   struct wl_registry *wl_registry;
   struct wl_drm *wl_server_drm;
   struct wl_drm *wl_drm;
   uint32_t wl_drm_version, wl_drm_name;
   struct wl_shm *wl_shm;
   struct wl_event_queue *wl_queue;
   struct zwp_linux_dmabuf_v1 *wl_dmabuf;
   struct dri2_wl_formats formats;
   struct zwp_linux_dmabuf_feedback_v1 *wl_dmabuf_feedback;
   struct dmabuf_feedback_format_table format_table;
   bool authenticated;
   uint32_t capabilities;
   char *device_name;
#endif

#ifdef HAVE_ANDROID_PLATFORM
   const gralloc_module_t *gralloc;
   /* gralloc vendor usage bit for front rendering */
   uint32_t front_rendering_usage;
#endif

   bool is_render_node;
   bool is_different_gpu;
};

可以通过_EGLDisplay的成员DriverData找到dri2_egl_display，并且dri2_dpy是一个非常重要的结构体！

_EGLDisplay *disp
struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);

__DRIscreen dri_screen pipe_screen之间关联

各种srceend的起点，是从dri2_egl_display开始的，它们之间的关联如下:

struct dri2_egl_display
{
    ...
    __DRIscreen *dri_screen;
    ...
}

//这块image_driver和dri2的extensions怎么赋值来的，后面会具体分析
dri2_dpy->dri_screen = dri2_dpy->image_driver->createNewScreen2(...)或者
dri2_dpy->dri_screen = dri2_dpy->dri2->createNewScreen2(...)

我们接下来看看__DRIscreen的定义

typedef struct __DRIscreenRec		__DRIscreen;

struct __DRIscreenRec {
    /**
        static const struct __DRIDriverVtableExtensionRec galliumdrm_vtable = {
           .base = { __DRI_DRIVER_VTABLE, 1 },
           .vtable = &galliumdrm_driver_api,
        };    
        这里的driver指向galliumdrm_driver_api
        psp->driver =
             ((__DRIDriverVtableExtension *)driver_extensions[i])->vtable;    
    **/
    const struct __DriverAPIRec *driver;


    int myNum;


    int fd;


    void *driverPrivate;

    void *loaderPrivate;



    const __DRIextension **extensions;

    const __DRIswrastLoaderExtension *swrast_loader;
    const __DRIkopperLoaderExtension *kopper_loader;

    struct {
	const __DRIdri2LoaderExtension *loader;
	const __DRIimageLookupExtension *image;
	const __DRIuseInvalidateExtension *useInvalidate;
        const __DRIbackgroundCallableExtension *backgroundCallable;
    } dri2;

    struct {
        const __DRIimageLoaderExtension *loader;
    } image;

    struct {
       const __DRImutableRenderBufferLoaderExtension *loader;
    } mutableRenderBuffer;

    driOptionCache optionInfo;
    driOptionCache optionCache;

    unsigned int api_mask;
};

结构体dri_screen定义:

struct dri_screen
{

   struct st_manager base;


   __DRIscreen *sPriv;//指向__DRIscreen
   boolean throttle;

   struct st_config_options options;

   /* Which postprocessing filters are enabled. */
   unsigned pp_enabled[PP_FILTERS];

   /* drm */
   int fd;
   boolean can_share_buffer;

   struct pipe_loader_device *dev;



   /* hooks filled in by dri2 & drisw */
   __DRIimage * (*lookup_egl_image)(struct dri_screen *ctx, void *handle);
   boolean (*validate_egl_image)(struct dri_screen *ctx, void *handle);
   __DRIimage * (*lookup_egl_image_validated)(struct dri_screen *ctx, void *handle);

   /* DRI exts that vary based on gallium pipe_screen caps. */
   __DRIimageExtension image_extension;
   __DRI2bufferDamageExtension buffer_damage_extension;

   /* DRI exts on this screen. Populated at init time based on device caps. */
   const __DRIextension *screen_extensions[14];
  ...

};

struct st_manager
{
   struct pipe_screen *screen;//这里又和pipe_screen勾搭上了
   ...
}

dri_screen和__DRIscreen是如何建立联系的，或者说他们之间的关系是什么:

__DRIscreen * sPriv
struct dri_screen *screen;
struct pipe_screen *pscreen = NULL;

screen->sPriv = sPriv;
sPriv->driverPrivate = (void *)screen;

真可以说的上是你中有我，我中有你的典范啊。相互关联对方！

dri_screen和pipe_screen是如何建立联系的，或者说他们之间的关系是什么:

这里就不兜圈子了，直接上关系:

//src/gallium/frontends/dri/dri_screen.c
const __DRIconfig **
dri_init_screen_helper(struct dri_screen *screen,
                       struct pipe_screen *pscreen)
{
   screen->base.screen = pscreen;
   ...
}

最后可以得到如下的一张关系表，其中厂家会对dri_screen进行扩展，通过结构体的继承

二.Mesa下eglInitialize初始化流程

搞通了这个流程，基本把Mesa的基本框架打通了。这里我们一步一步来分析，不具体代码详细分析，只有关键地方会详细分析：

//src/egl/drivers/dri2/egl_dri2.c
const _EGLDriver _eglDriver = {
   .Initialize = dri2_initialize,
   .Terminate = dri2_terminate,
   .CreateContext = dri2_create_context,
   .DestroyContext = dri2_destroy_context,
   .MakeCurrent = dri2_make_current,
   .CreateWindowSurface = dri2_create_window_surface,
   .CreatePixmapSurface = dri2_create_pixmap_surface,
   .CreatePbufferSurface = dri2_create_pbuffer_surface,
   .DestroySurface = dri2_destroy_surface,
   .GetProcAddress = dri2_get_proc_address,
   .WaitClient = dri2_wait_client,
   .WaitNative = dri2_wait_native,
   .BindTexImage = dri2_bind_tex_image,
   .ReleaseTexImage = dri2_release_tex_image,
   .SwapInterval = dri2_swap_interval,
   .SwapBuffers = dri2_swap_buffers,
   .SwapBuffersWithDamageEXT = dri2_swap_buffers_with_damage,
   .SwapBuffersRegionNOK = dri2_swap_buffers_region,
   .SetDamageRegion = dri2_set_damage_region,
   .PostSubBufferNV = dri2_post_sub_buffer,
   .CopyBuffers = dri2_copy_buffers,
   .QueryBufferAge = dri2_query_buffer_age,
   .CreateImageKHR = dri2_create_image,
   .DestroyImageKHR = dri2_destroy_image_khr,
   .CreateWaylandBufferFromImageWL = dri2_create_wayland_buffer_from_image,
   .QuerySurface = dri2_query_surface,
   .QueryDriverName = dri2_query_driver_name,
   .QueryDriverConfig = dri2_query_driver_config,
#ifdef HAVE_LIBDRM
   .CreateDRMImageMESA = dri2_create_drm_image_mesa,
   .ExportDRMImageMESA = dri2_export_drm_image_mesa,
   .ExportDMABUFImageQueryMESA = dri2_export_dma_buf_image_query_mesa,
   .ExportDMABUFImageMESA = dri2_export_dma_buf_image_mesa,
   .QueryDmaBufFormatsEXT = dri2_query_dma_buf_formats,
   .QueryDmaBufModifiersEXT = dri2_query_dma_buf_modifiers,
#endif
#ifdef HAVE_WAYLAND_PLATFORM
   .BindWaylandDisplayWL = dri2_bind_wayland_display_wl,
   .UnbindWaylandDisplayWL = dri2_unbind_wayland_display_wl,
   .QueryWaylandBufferWL = dri2_query_wayland_buffer_wl,
#endif
   .GetSyncValuesCHROMIUM = dri2_get_sync_values_chromium,
   .GetMscRateANGLE = dri2_get_msc_rate_angle,
   .CreateSyncKHR = dri2_create_sync,
   .ClientWaitSyncKHR = dri2_client_wait_sync,
   .SignalSyncKHR = dri2_signal_sync,
   .WaitSyncKHR = dri2_server_wait_sync,
   .DestroySyncKHR = dri2_destroy_sync,
   .GLInteropQueryDeviceInfo = dri2_interop_query_device_info,
   .GLInteropExportObject = dri2_interop_export_object,
   .GLInteropFlushObjects = dri2_interop_flush_objects,
   .DupNativeFenceFDANDROID = dri2_dup_native_fence_fd,
   .SetBlobCacheFuncsANDROID = dri2_set_blob_cache_funcs,
};

eglInitialize(...)//src/egl/main/eglapi.c
    _eglDriver.Initialize(disp)
        dri2_initialize(...)//src/egl/drivers/dri2/egl_dri2.c
            dri2_initialize_android(disp)//src/egl/drivers/dri2/platform_android.c
    

这里我们对dri2_initialize_android拿出来，另开分析，只是让后面自己回过头看更加清楚！

dri2_initialize_android(_EGLDisplay *disp)
    struct dri2_egl_display *dri2_dpy;
    dri2_dpy = calloc(1, sizeof(*dri2_dpy));
    disp->DriverData = (void *) dri2_dpy;
    ret = hw_get_module(GRALLOC_HARDWARE_MODULE_ID,
                   (const hw_module_t **)&dri2_dpy->gralloc);
    device_opened = droid_open_device(disp, disp->Options.ForceSoftware);
    dri2_dpy->vtbl = &droid_display_vtbl;
    
    
droid_open_device(...)// src/egl/drivers/dri2/platform_android.c
    struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp)
    dri2_dpy->fd = loader_open_device(device->nodes[node_type])
    droid_probe_device(...)
        droid_load_driver(..)//这个非常重要，加载驱动
                dri2_dpy->loader_extensions = droid_image_loader_extensions;
                dri2_load_driver_dri3(...)
        dri2_create_screen(...)//构建screen，关于scrren的关系图前面已经放出来了,详见章节3
        

我们接下来分析dri2_load_driver_dri3的调用流程，代码流程比较多，只能一步步的来:

static const struct dri2_extension_match dri3_driver_extensions[] = {
   { __DRI_CORE, 1, offsetof(struct dri2_egl_display, core) },
   { __DRI_IMAGE_DRIVER, 1, offsetof(struct dri2_egl_display, image_driver) },
   { NULL, 0, 0 }
};
dri2_load_driver_dri3(...)//src/egl/drivers/dri2/egl_dri2.c
    dri2_load_driver_common(disp, dri3_driver_extensions)
        extensions = dri2_open_driver(disp)//详见章节2.1
        dri2_bind_extensions(dri2_dpy, driver_extensions, extensions, false)//详见章节2.2
        dri2_dpy->driver_extensions = extensions
        

2.1 dri2_open_driver

我们接下来重点分析该函数:

 
 
dri2_open_driver()//src/egl/drivers/dri2/egl_dri2.c
    const struct __DRIextensionRec **(*get_extensions)(void);
    void *driver = loader_open_driver_lib(driver_name, "_dri", search_path_vars,
                                         DEFAULT_DRIVER_DIR, true);//加载dri库
    get_extensions_name = loader_get_extensions_name(driver_name)//拼接驱动extensions名称，这里的拼接后是__driDriverGetExtensions_xxx_gpu
    get_extensions = dlsym(driver, get_extensions_name)//加载函数符号表等

这里的__driDriverGetExtensions_xxx_gpu函数符号表是怎么拼凑成的了，如果我们通过grep在mesa搜索，怎么搜索也搜不到了。它是通过宏定义实现的。它的定义如下:

//src/gallium/targets/dri/target.c
#define DEFINE_LOADER_DRM_ENTRYPOINT(drivername)                          \
const __DRIextension **__driDriverGetExtensions_##drivername(void);       \
PUBLIC const __DRIextension **__driDriverGetExtensions_##drivername(void) \
{                                                                         \
   return galliumdrm_driver_extensions;                                   \
}

#if defined(GALLIUM_MWV207)
DEFINE_LOADER_DRM_ENTRYPOINT(xxx_gpu);  //这里我们也可以扩展，自己的驱动，譬如XXX参照这个
#endif

这里我们重点关注galliumdrm_driver_extensions的实现，我们接着继续往下看：

注意它的实现在代码是在frontends前端目录代码下

//src/gallium/frontends/dri/dri2.c
const __DRIextension *galliumdrm_driver_extensions[] = {
    &driCoreExtension.base,
    &driImageDriverExtension.base,
    &driDRI2Extension.base,
    &gallium_config_options.base,
    &galliumdrm_vtable.base,
    NULL
};

//src/gallium/frontends/dri/dri_util.c
/** Core interface */
const __DRIcoreExtension driCoreExtension = {
    .base = { __DRI_CORE, 2 },

    .createNewScreen            = NULL,
    .destroyScreen              = driDestroyScreen,
    .getExtensions              = driGetExtensions,
    .getConfigAttrib            = driGetConfigAttrib,
    .indexConfigAttrib          = driIndexConfigAttrib,
    .createNewDrawable          = NULL,
    .destroyDrawable            = driDestroyDrawable,
    .swapBuffers                = driSwapBuffers, /* swrast */
    .createNewContext           = driCreateNewContext, /* swrast */
    .copyContext                = driCopyContext,
    .destroyContext             = driDestroyContext,
    .bindContext                = driBindContext,
    .unbindContext              = driUnbindContext
};

/** Image driver interface */
const __DRIimageDriverExtension driImageDriverExtension = {
    .base = { __DRI_IMAGE_DRIVER, 1 },

    .createNewScreen2           = driCreateNewScreen2,
    .createNewDrawable          = driCreateNewDrawable,
    .getAPIMask                 = driGetAPIMask,
    .createContextAttribs       = driCreateContextAttribs,
};


/** DRI2 interface */
const __DRIdri2Extension driDRI2Extension = {
    .base = { __DRI_DRI2, 4 },

    .createNewScreen            = dri2CreateNewScreen,
    .createNewDrawable          = driCreateNewDrawable,
    .createNewContext           = driCreateNewContext,
    .getAPIMask                 = driGetAPIMask,
    .createNewContextForAPI     = driCreateNewContextForAPI,
    .allocateBuffer             = dri2AllocateBuffer,
    .releaseBuffer              = dri2ReleaseBuffer,
    .createContextAttribs       = driCreateContextAttribs,
    .createNewScreen2           = driCreateNewScreen2,
};


//src/gallium/frontends/dri/dri2.c
static const struct __DRIDriverVtableExtensionRec galliumdrm_vtable = {
   .base = { __DRI_DRIVER_VTABLE, 1 },
   .vtable = &galliumdrm_driver_api,
};

2.2 dri2_bind_extensions

我们接下来重点分析该函数:

static EGLBoolean
dri2_bind_extensions(struct dri2_egl_display *dri2_dpy,
                     const struct dri2_extension_match *matches,
                     const __DRIextension **extensions,
                     bool optional)
{
   int ret = EGL_TRUE;
   void *field;

   for (int i = 0; extensions[i]; i++) {
      _eglLog(_EGL_DEBUG, "found extension `%s'", extensions[i]->name);
      for (int j = 0; matches[j].name; j++) {
         if (strcmp(extensions[i]->name, matches[j].name) == 0 &&
             extensions[i]->version >= matches[j].version) {
            field = ((char *) dri2_dpy + matches[j].offset);
            *(const __DRIextension **) field = extensions[i];
            _eglLog(_EGL_INFO, "found extension %s version %d",
                    extensions[i]->name, extensions[i]->version);
            break;
         }
      }
   }

   for (int j = 0; matches[j].name; j++) {
      field = ((char *) dri2_dpy + matches[j].offset);
      if (*(const __DRIextension **) field == NULL) {
         if (optional) {
            _eglLog(_EGL_DEBUG, "did not find optional extension %s version %d",
                    matches[j].name, matches[j].version);
         } else {
            _eglLog(_EGL_WARNING, "did not find extension %s version %d",
                    matches[j].name, matches[j].version);
            ret = EGL_FALSE;
         }
      }
   }

   return ret;
}

我们可以理解这个函数，这个函数主要是填充dri2_egl_display中的各个extensions扩展，譬如:

//src/egl/drivers/dri2/egl_dri2.h
struct dri2_egl_display
{
    ...
   const __DRIcoreExtension *core;
   const __DRIimageDriverExtension *image_driver;
   const __DRIdri2Extension *dri2;
   const __DRIswrastExtension *swrast;
   const __DRIkopperExtension *kopper;
   const __DRI2flushExtension *flush;
   const __DRI2flushControlExtension *flush_control;
   const __DRItexBufferExtension *tex_buffer;
   const __DRIimageExtension *image;
   const __DRIrobustnessExtension *robustness;
   const __DRI2configQueryExtension *config;
   const __DRI2fenceExtension *fence;
   const __DRI2bufferDamageExtension *buffer_damage;
   const __DRI2blobExtension *blob;
   const __DRI2rendererQueryExtension *rendererQuery;
   const __DRI2interopExtension *interop;
   const __DRIconfigOptionsExtension *configOptions;
   const __DRImutableRenderBufferDriverExtension *mutable_render_buffer;    
    ...
}

三. dri2_create_screen的实现

万里长征刚开始，到这里还只是第一步啊，得接续往下走，我们接着接续分析！

//src/egl/drivers/dri2/egl_dri2.c
dri2_create_screen(...)
    dri2_dpy->dri_screen = dri2_dpy->image_driver->createNewScreen2(....)

这里的dri2_dpy->image_driver指向那里呢，这里可以在章节2.1和章节2.2找到答案，它指向了dri_util.c里面的结构体driImageDriverExtension，如下:

//src/gallium/frontends/dri/dri_util.c
/** Image driver interface */
const __DRIimageDriverExtension driImageDriverExtension = {
    .base = { __DRI_IMAGE_DRIVER, 1 },

    .createNewScreen2           = driCreateNewScreen2,
    .createNewDrawable          = driCreateNewDrawable,
    .getAPIMask                 = driGetAPIMask,
    .createContextAttribs       = driCreateContextAttribs,
};

所以我们继续看driCreateNewScreen2的实现:

//src/gallium/frontends/dri/dri_util.c
driCreateNewScreen2(...)
    __DRIscreen *psp
    psp = calloc(1, sizeof(*psp))
    psp->driver =
        ((__DRIDriverVtableExtension *)driver_extensions[i])->vtable;//指向galliumdrm_driver_api
    psp->driver->InitScreen(psp)//这里会指向galliumdrm_driver_api中dri2_init_screen，在dri2.c中实现

我们接着来看dri2_init_screen的实现:

//src/gallium/frontends/dri/dri2.c
static const __DRIconfig **
dri2_init_screen(__DRIscreen * sPriv)
{
   const __DRIconfig **configs;
   struct dri_screen *screen;//各种screen开始出现
   struct pipe_screen *pscreen = NULL;

   screen = CALLOC_STRUCT(dri_screen);//构建一个，还没有开始初始化


   screen->sPriv = sPriv;//开始指向，并赋值了
   screen->fd = sPriv->fd;
   
   sPriv->driverPrivate = (void *)screen;//相互引用
   
   
   if (pipe_loader_drm_probe_fd(&screen->dev, screen->fd)) {//详见章节3.1
      pscreen = pipe_loader_create_screen(screen->dev);//详见章节3.2
      dri_init_options(screen);
    }
    
   dri2_init_screen_extensions(screen, pscreen, false);
   configs = dri_init_screen_helper(screen, pscreen);
   
   ...
}

为了排版简介明了一些，这里我们不全部放在一个大章节里面，而是进行小章节，这样排版会更加合理看起来也更加的舒服！

3.1 pipe_loader_drm_probe_fd

我们接着继续往下分析该源码的实现:

//src/gallium/auxiliary/pipe-loader/pipe_loader_drm.c

static struct pipe_screen *
pipe_loader_drm_create_screen(struct pipe_loader_device *dev,
                              const struct pipe_screen_config *config, bool sw_vk)
{
   struct pipe_loader_drm_device *ddev = pipe_loader_drm_device(dev);

   return ddev->dd->create_screen(ddev->fd, config);
}

static const struct pipe_loader_ops pipe_loader_drm_ops = {
   .create_screen = pipe_loader_drm_create_screen,
   .get_driconf = pipe_loader_drm_get_driconf,
   .release = pipe_loader_drm_release
};

pipe_loader_drm_probe_fd(...)
    pipe_loader_drm_probe_fd_nodup(struct pipe_loader_device **dev, int fd)
        struct pipe_loader_drm_device *ddev = CALLOC_STRUCT(pipe_loader_drm_device);
        ddev->base.ops = &pipe_loader_drm_ops;
        ddev->fd = fd;
        ddev->base.driver_name = loader_get_driver_for_fd(fd)
        ddev->dd = get_driver_descriptor(ddev->base.driver_name, plib)
        *dev = &ddev->base;

我们接着看get_driver_descriptor的实现，看看它究竟在干啥！

//src/gallium/auxiliary/pipe-loader/pipe_loader_drm.c
#ifdef GALLIUM_STATIC_TARGETS
static const struct drm_driver_descriptor *driver_descriptors[] = {
   &i915_driver_descriptor,
   &iris_driver_descriptor,
   &crocus_driver_descriptor,
   &nouveau_driver_descriptor,
   &r300_driver_descriptor,
   &r600_driver_descriptor,
   &radeonsi_driver_descriptor,
   &vmwgfx_driver_descriptor,
   &kgsl_driver_descriptor,
   &msm_driver_descriptor,
   &virtio_gpu_driver_descriptor,
   &v3d_driver_descriptor,
   &vc4_driver_descriptor,
   &panfrost_driver_descriptor,
   &asahi_driver_descriptor,
   &etnaviv_driver_descriptor,
   &tegra_driver_descriptor,
   &lima_driver_descriptor,
   &zink_driver_descriptor,
   &xxx_gpu_driver_descriptor,
};
#endif


static const struct drm_driver_descriptor *
get_driver_descriptor(const char *driver_name, struct util_dl_library **plib)
{
#ifdef GALLIUM_STATIC_TARGETS
   for (int i = 0; i < ARRAY_SIZE(driver_descriptors); i++) {
      if (strcmp(driver_descriptors[i]->driver_name, driver_name) == 0)
         return driver_descriptors[i];
   }
   return &kmsro_driver_descriptor;
#else
    ...
#endif
    ...
}

那么这里的xxx_driver_descriptor是怎么实现的，刚开始我通过grep搜索发现只有定义，没有怎么实现。尼玛见鬼了不成，这又是套路啊，又是通过各种宏来实现的。我们看看它是怎么实现的(这里我以景嘉微的xxx_gpu为例来说明)。

//src/gallium/auxiliary/target-helpers/drm_helper.h

/**
 * Instantiate a drm_driver_descriptor struct.
 */
#define DEFINE_DRM_DRIVER_DESCRIPTOR(descriptor_name, driver, _driconf, _driconf_count, func) \
const struct drm_driver_descriptor descriptor_name = {         \
   .driver_name = #driver,                                     \
   .driconf = _driconf,                                        \
   .driconf_count = _driconf_count,                            \
   .create_screen = func,                                      \
};

#define DRM_DRIVER_DESCRIPTOR(driver, driconf, driconf_count)                          \
   DEFINE_DRM_DRIVER_DESCRIPTOR(driver##_driver_descriptor, driver, driconf, driconf_count, pipe_##driver##_create_screen)


#include "xxx_gpu/drm/xxx_gpu_drm_public.h"

static struct pipe_screen *
pipe_xxx_gpu_create_screen(int fd, const struct pipe_screen_config *config)
{
   struct pipe_screen *screen;

   screen = xxx_gpu_drm_create_screen(fd);
   return screen ? debug_screen_wrap(screen) : NULL;
}

DRM_DRIVER_DESCRIPTOR(xxx_gpu, NULL, 0)

所以分析到这里我们获得了ddev->dd的指向，它指向了vendor实现的结构体drm_driver_descriptor。搞清楚了这个我们接着继续看 ddev->dd->create_screen的实现，它指向了pipe_xxx_gpu_create_screen，我们接着分析:

//src/gallium/auxiliary/target-helpers/drm_helper.h
static struct pipe_screen *
pipe_xxx_gpu_create_screen(int fd, const struct pipe_screen_config *config)
{
   struct pipe_screen *screen;

   screen = xxx_gpu_drm_create_screen(fd);//返回封装好的pipe_screen
        struct xxx_gpu_winsys *ws;
        ws = CALLOC_STRUCT(xxx_gpu_winsys)
        ws->screen = xxx_gpu_create_screen(ws)
        return ws->screen
   return screen ? debug_screen_wrap(screen) : NULL;
}

3.2 pipe_loader_create_screen

分析完了pipe_loader_drm_probe_fd流程，我们接着咔咔一顿接着继续分析，pipe_loader_create_screen它会构建pipe_screen的结构体类型！

pipe_loader_create_screen(...)//src/gallium/frontends/dri/dri2.c
    pipe_loader_create_screen(...)//src/gallium/auxiliary/pipe-loader/pipe_loader.c
        pipe_loader_create_screen_vk(...)
            dev->ops->create_screen(...)//这里的ops指向了pipe_loader_drm_ops，定义在pipe_loader_drm.c  
                pipe_loader_drm_create_screen(...)
                    ddev->dd->create_screen(...)//这里的ddev->dd指向了前面获取的结构体
                        pipe_xxx_gpu_create_screen(...)

到这里整个流程就基本结束了。后续如果需要查看的，可以继续dri2_init_screen研究，主要是要理清楚几个screen之间的关系！