v4l2驱动1-linux-3.0.8的v4l2_dev.h分析

看一下drivers/media/video下的Makefile你会发现：

videodev-objs:=v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-fh.o \

                        v4l2-event.o v4l2-ctrls.o v4l2-subdev.o

这是生成videodev.ko必要的文件。网上有很多讲解v4l2驱动编写的文章。推荐网址：

这是主要说用户使用：

http://linuxtv.org/downloads/v4l-dvb-apis/

这是说驱动编写：

http://lwn.net/Articles/203924/

对应的中文翻译（用户的不是很全）

http://download.csdn.net/detail/xxxxxlllllxl/7076235

我的博客将从Makefile中涉及的文件对应的头文件去分析：先从v4l2_dev.h开始

/* * *V 4 L 2   D R I V E R   H E L P E R   A P I * * Moved from videodev2.h//从videodev2.h中移出来的 * *Some commonly needed functions for drivers (v4l2-common.o module) */#ifndef _V4L2_DEV_H#define _V4L2_DEV_H#include <linux/poll.h>#include <linux/fs.h>#include <linux/device.h>#include <linux/cdev.h>#include <linux/mutex.h>#include <linux/videodev2.h>#include <media/media-entity.h>#define VIDEO_MAJOR81//下面不同的宏生成的设备名不一样#define VFL_TYPE_GRABBER0 //"video"#define VFL_TYPE_VBI1 //"vbi"#define VFL_TYPE_RADIO2 //"radio"#define VFL_TYPE_SUBDEV3 //"v4l-subdev"#define VFL_TYPE_MAX4struct v4l2_ioctl_callbacks;struct video_device;struct v4l2_device;struct v4l2_ctrl_handler;/* Flag to mark the video_device struct as registered.   Drivers can clear this flag if they want to block all future   device access. It is cleared by video_unregister_device. */#define V4L2_FL_REGISTERED(0)//标记设备是否被注册/* file->private_data points to struct v4l2_fh */#define V4L2_FL_USES_V4L2_FH(1) //使用文件操作/* Use the prio field of v4l2_fh for core priority checking */#define V4L2_FL_USE_FH_PRIO(2) //文件操作中使用优先级检查/* Priority helper functions */ //优先级帮助功能struct v4l2_prio_state {atomic_t prios[4];};/*enum v4l2_priority {V4L2_PRIORITY_UNSET       = 0,  //不初始化V4L2_PRIORITY_BACKGROUND  = 1,  //背景V4L2_PRIORITY_INTERACTIVE = 2,  //互动V4L2_PRIORITY_RECORD      = 3,  //记录V4L2_PRIORITY_DEFAULT     = V4L2_PRIORITY_INTERACTIVE,};*///优先级是为了Multiple Opens操作，当可以支持设备同事被多个线程打开时//需要用这优先级去区分那个操作更重要，用那个优先级，那个优先级几上面//的prios[4]就加一，不用就减一。void v4l2_prio_init(struct v4l2_prio_state *global); //初始化，就是global清零int v4l2_prio_change(struct v4l2_prio_state *global, enum v4l2_priority *local,     enum v4l2_priority new); //改变优先级，对应prios改变，local会等于newvoid v4l2_prio_open(struct v4l2_prio_state *global, enum v4l2_priority *local);//打开，对应的prios[*local]加一void v4l2_prio_close(struct v4l2_prio_state *global, enum v4l2_priority local);//关闭，对应的prios[local]减一enum v4l2_priority v4l2_prio_max(struct v4l2_prio_state *global);//当前已打开的最大优先级。int v4l2_prio_check(struct v4l2_prio_state *global, enum v4l2_priority local);//检查local显示优先级是否是当前打开的最大的优先级struct v4l2_file_operations {struct module *owner;ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);unsigned int (*poll) (struct file *, struct poll_table_struct *);long (*ioctl) (struct file *, unsigned int, unsigned long);long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);unsigned long (*get_unmapped_area) (struct file *, unsigned long,unsigned long, unsigned long, unsigned long);int (*mmap) (struct file *, struct vm_area_struct *);int (*open) (struct file *);int (*release) (struct file *);};/*对应上面的ops我要说几点：1. get_unmapped_area，这个最终赋给file_operations对应的函数。   这是系统sys_mmap2使用的函数，会判断虚拟内存空间中是否有足   够的空间的工作。2. read/write读流   使用read和write方法，每一帧都要通过I/O 操作，在用户和内核   空间之间拷贝数据。设备cap要或上V4L2_CAP_READWRITE3. ioctl和unlocked_ioctl   这两个都通过file_operations中的unlocked_ioctl调用，v4l2的   unlocked_ioctl会优先调用，ioctl可以认为是序列化的ioctl,会   上锁等待上一个ioctl完成，如果在驱动睡眠下会很糟糕。4. ioctl读流   在设备cap上要或上V4L2_CAP_STREAMING，让用户与内核空间之间   交换缓冲区指针，这些缓冲区将被映射到用户地址空间，使帧的零   拷贝成为可能。   “用户与内核空间之间交换缓冲区指针”我们要理解的是缓冲区是   在用户空间还是内核空间。对于内核空间我们通过mmap()方法映射。   对于用户空间就不需要mmap()，此方法比较难用。*//* * Newer version of video_device, handled by videodev2.c * This version moves redundant code from video device code to *the common handler */struct video_device{#if defined(CONFIG_MEDIA_CONTROLLER)struct media_entity entity;#endif/* device ops */const struct v4l2_file_operations *fops;/* sysfs */ struct device dev;/* v4l device */  //这个dev主要是为了sysfs用的struct cdev *cdev;/* character device */ //这个cdev就是我们生成对应的video字符设备/* Set either parent or v4l2_dev if your driver uses v4l2_device */struct device *parent;/* device parent */struct v4l2_device *v4l2_dev;/* v4l2_device parent *//* Control handler associated with this device node. May be NULL. */struct v4l2_ctrl_handler *ctrl_handler;//这是多video设备控制用的，等说到v4l2_ctrls.h再细说/* Priority state. If NULL, then v4l2_dev->prio will be used. */struct v4l2_prio_state *prio;//上面说的优先级/* device info */char name[32]; //设备名，这个设备名是在/sysfs下显示用的int vfl_type; //对应上面的VFL_*/* 'minor' is set to -1 if the registration failed */int minor;u16 num;//记录注册的video设备节点号/* use bitops to set/clear/test flags */unsigned long flags;//主要对应上面的V4L2_FL_*/* attribute to differentiate multiple indices on one physical device */int index;//通过get_index()获取一个可用设备索引。/* V4L2 file handles *///文件操作。v4l2_fh.h再说spinlock_tfh_lock; /* Lock for all v4l2_fhs */struct list_headfh_list; /* List of struct v4l2_fh */int debug;/* Activates debug level*///V4L2_DEBUG_*，不同的赋值，打印出的信息数量不一样/* Video standard vars */ //视频标准规范，对应V4L2_STD_*，如我们熟悉的PAL、NTSC。v4l2_std_id tvnorms;/* Supported tv norms */  //支持的标准v4l2_std_id current_norm;/* Current tvnorm */ //当前使用的标准/* callbacks */void (*release)(struct video_device *vdev);//这个必须有，很多驱动使用video_device_release。/* ioctl callbacks */ //v4l2-ioctl.h我们再慢慢说它const struct v4l2_ioctl_ops *ioctl_ops;/* serialization lock */struct mutex *lock;};#define media_entity_to_video_device(__e) \container_of(__e, struct video_device, entity)/* dev to video-device */#define to_video_device(cd) container_of(cd, struct video_device, dev)//这个注册主要说一下warn_if_nr_in_use,就是如果你指定一个nr，但是驱动会使用另一个代替时会打印警告int __must_check __video_register_device(struct video_device *vdev, int type,int nr, int warn_if_nr_in_use, struct module *owner);/* Register video devices. Note that if video_register_device fails,   the release() callback of the video_device structure is *not* called, so   the caller is responsible for freeing any data. Usually that means that   you call video_device_release() on failure. */static inline int __must_check video_register_device(struct video_device *vdev,int type, int nr){return __video_register_device(vdev, type, nr, 1, vdev->fops->owner);}/* Same as video_register_device, but no warning is issued if the desired   device node number was already in use. */static inline int __must_check video_register_device_no_warn(struct video_device *vdev, int type, int nr){return __video_register_device(vdev, type, nr, 0, vdev->fops->owner);}/* Unregister video devices. Will do nothing if vdev == NULL or   video_is_registered() returns false. */void video_unregister_device(struct video_device *vdev);/* helper functions to alloc/release struct video_device, the   latter can also be used for video_device->release(). */struct video_device * __must_check video_device_alloc(void); //分配video_device结构体/* this release function frees the vdev pointer */void video_device_release(struct video_device *vdev); //释放/* this release function does nothing, use when the video_device is a   static global struct. Note that having a static video_device is   a dubious construction at best. */void video_device_release_empty(struct video_device *vdev);//空函数/* helper functions to access driver private data. */static inline void *video_get_drvdata(struct video_device *vdev) //获取私有数据{return dev_get_drvdata(&vdev->dev);}static inline void video_set_drvdata(struct video_device *vdev, void *data)//设置私有数据{dev_set_drvdata(&vdev->dev, data);}struct video_device *video_devdata(struct file *file);//根据file得到对应的video_device/* Combine video_get_drvdata and video_devdata as this is   used very often. */static inline void *video_drvdata(struct file *file) //结合上面看{return video_get_drvdata(video_devdata(file));}static inline const char *video_device_node_name(struct video_device *vdev){return dev_name(&vdev->dev);}static inline int video_is_registered(struct video_device *vdev)//是否已注册{return test_bit(V4L2_FL_REGISTERED, &vdev->flags);}#endif /* _V4L2_DEV_H */