虛擬視頻驅(qū)動(dòng)程序vivi.c源碼分析 以下先把上一篇文章中的最后一段，放在這里利于程序源碼的分析： vivi.c 虛擬視頻驅(qū)動(dòng)程序----- 此代碼模擬一個(gè)真正的視頻設(shè)備V4L2 API (位于drivers/media/video目錄下) 入口：+int __init vivi_init(void) ? ? ? ? ? ? ? ?+ vivi_create_instance(i) /*創(chuàng)建設(shè)備*//**/。 ? ? ? ? ? ? ? ? ? ? ? ?+ 分配一個(gè)vivi_dev的結(jié)構(gòu)體 /*它嵌套這結(jié)構(gòu)體v4l2_device 和video_device*/ ? ? ? ? ? ? ? ? ? ? ? ?+ v4l2_device_register(NULL, &dev->v4l2_dev);/*注冊(cè)vivi_dev中的V4l2_device*/ ? ? ? ? ? ? ? ? ? ? ? ?+ 初始化視頻的DMA隊(duì)列 ? ? ? ? ? ? ? ? ? ? ? ?+ 初始化鎖 ? ? ? ? ? ? ? ? ? ? ? ?+ video_device_alloc(); 動(dòng)態(tài)分配video_device結(jié)構(gòu)體 ? ? ? ? ? ? ? ? ? ? ? ?+ 構(gòu)建一個(gè)video_device結(jié)構(gòu)體 vivi_template 并賦給上面分配的video_device ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? static struct video_device vivi_template = { ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .name ? ? ? ?= "vivi", ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .fops ? ? ? ? ? = &vivi_fops, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .ioctl_ops ? ? = &vivi_ioctl_ops, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .minor ? ? ? ?= -1, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .release ? ?= video_device_release, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .tvnorms ? ? ? ? ? ? ?= V4L2_STD_525_60, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .current_norm ? ? ? ? = V4L2_STD_NTSC_M, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?}; ? ? ? ? ? ? ? ? ? ? ?+ video_set_drvdata(vfd, dev);設(shè)置驅(qū)動(dòng)程序?qū)Ｓ袛?shù)據(jù) ? ? ? ? ? ? ? ? ? ? ?+ 所有控件設(shè)置為其默認(rèn)值 ? ? ? ? ? ? ? ? ? ? ?+ list_add_tail(&dev->vivi_devlist, &vivi_devlist);添加到設(shè)備列表 ? ? ? ? + 構(gòu)建 v4l2_file_operations 結(jié)構(gòu)體vivi_fops 并實(shí)現(xiàn).open .release .read .poll .mmap函數(shù)----- .ioctl 用標(biāo)準(zhǔn)的v4l2控制處理程序 ? ? ? ? + 構(gòu)建 v4l2_ioctl_ops結(jié)構(gòu)體 vivi_ioctl_ops ? ? ? ? ? ? ? ? ? ? ? ? ? ?static const struct v4l2_ioctl_ops vivi_ioctl_ops = { ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_querycap ? ? ?= vidioc_querycap, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_enum_fmt_vid_cap ?= vidioc_enum_fmt_vid_cap, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_try_fmt_vid_cap ? = vidioc_try_fmt_vid_cap, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_s_fmt_vid_cap ? ? = vidioc_s_fmt_vid_cap, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_reqbufs ? ? ? = vidioc_reqbufs, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_querybuf ? ? ?= vidioc_querybuf, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_qbuf ? ? ? ? ?= vidioc_qbuf, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_dqbuf ? ? ? ? = vidioc_dqbuf, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_s_std ? ? ? ? = vidioc_s_std, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_enum_input ? ?= vidioc_enum_input, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_g_input ? ? ? = vidioc_g_input, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_s_input ? ? ? = vidioc_s_input, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_queryctrl ? ? = vidioc_queryctrl, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_g_ctrl ? ? ? ?= vidioc_g_ctrl, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_s_ctrl ? ? ? ?= vidioc_s_ctrl, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_streamon ? ? ?= vidioc_streamon, ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidioc_streamoff ? ? = vidioc_streamoff, ? ? ? ? ? ? ? ? ? ? ? ? ? ?#ifdef CONFIG_VIDEO_V4L1_COMPAT ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .vidiocgmbuf ? ? ? ? ?= vidiocgmbuf, ? ? ? ? ? ? ? ? ? ? ? ? ? ?#endif ? ? ? ? ? ? ? ? ? ? ?}; ? ? ? ? ?+ int vivi_open(struct file *file) ? ? ? ? ? ? ? ? ? ?+ vivi_dev *dev = video_drvdata(file); ?訪(fǎng)問(wèn)驅(qū)動(dòng)程序?qū)Ｓ脭?shù)據(jù) ? ? ? ? ? ? ? ? ? ?+ 分配+初始化句柄（vivi_fh）數(shù)據(jù) ? ? ? ? ? ? ? ? ? ?+ 重置幀計(jì)數(shù)器 ? ? ? ? ? ? ? ? ? ?+ videobuf_queue_vmalloc_init(); 初始化視頻緩沖隊(duì)列 ? ? ? ? ? ? ? ? ? ?+ 開(kāi)啟一個(gè)新線(xiàn)程用于開(kāi)始和暫停 ? ? ? ? ?+ 實(shí)現(xiàn)自定義的v4l2_ioctl_ops 函數(shù) 現(xiàn)在開(kāi)始分析程序源碼，利于之后對(duì)V4L2驅(qū)動(dòng)的開(kāi)發(fā)，學(xué)習(xí) 首先就行驅(qū)動(dòng)的入口開(kāi)始：
static?int ?__init vivi_init( void) { ????const ?struct font_desc?* font?= ?find_font( "VGA8x16" ) ; ????int ?ret?= ?0, ?i; ????if ?( font?= = ?NULL ) ?{ ????????printk( KERN_ERR?"vivi: could not find font\n" ) ; ????????return?- ENODEV; ????} ????font8x16?= ?font- > data; ????if ?( n_devs?< = ?0) ????????n_devs?= ?1; ????for ?( i?= ?0; ?i?< ?n_devs; ?i+ + ) ?{ ????????/ / Here?is ?the most important ????????ret? = ?vivi_create_instance ( i ) ; ????????if ?( ret) ?{ ????????????/ * ?If ?some instantiations succeeded, ?keep driver?* / ????????????if ?( i) ????????????????ret?= ?0; ????????????break; ????????} ????} ????if ?( ret?< ?0) ?{ ????????printk( KERN_ERR?"vivi: error %d while loading driver\n" , ?ret) ; ????????return ret; ????} ????printk( KERN_INFO?"Video Technology Magazine Virtual Video " ????????????"Capture Board ver %u.%u.%u successfully loaded.\n" , ????????????( VIVI_VERSION?> > ?16) ?& ?0xFF, ?( VIVI_VERSION?> > ?8) ?& ?0xFF, ????????????VIVI_VERSION?& ?0xFF) ; ????/ * ?n_devs will reflect the actual number of allocated devices?* / ????n_devs?= ?i; ????return ret; } static void __exit vivi_exit( void) { ????vivi_release( ) ; } module_init ( vivi_init ) ; module_exit ( vivi_exit ) ; 這其實(shí)最重要的就是上面標(biāo)注備份，下面重點(diǎn)分析 vivi_create_instance 方法：
static?int ?__init vivi_create_instance( int ?inst) { ????struct vivi_dev?* dev; ????struct video_device?* vfd; ????struct v4l2_ctrl_handler?* hdl; ????struct vb2_queue?* q; ????int ?ret; ????dev?= ?kzalloc( sizeof( * dev) , ?GFP_KERNEL) ; ????if ?( ! dev) ????????return?- ENOMEM; ????/ / ?set ?the v4l2_device( the name) ????snprintf( dev- > v4l2_dev. name, ?sizeof( dev- > v4l2_dev. name) , ????????????"%s-%03d" , ?VIVI_MODULE_NAME, ?inst) ; ???? ????/ * ? ????* ?register the v4l2_device, ?but you should pay attention here ????* ?the?"dev == NULL" ?it means v4l2_device. dev?= = ?NULL ????* ?You did' t?set ?the v4l2_device. dev, ?you will?set ?it later ????* / ????ret? = ?v4l2_device_register ( NULL , ?& dev - > v4l2_dev ) ; ????if ?( ret) ????????goto free_dev; ????/ * ?init the handle, ?learn it later?* / ????dev- > fmt?= ?& formats[ 0] ; ????dev- > width?= ?640; ????dev- > height?= ?480; ????hdl? = ?& dev - > ctrl_handler ; ????v4l2_ctrl_handler_init ( hdl , ?11 ) ; ????dev- > volume?= ?v4l2_ctrl_new_std( hdl, ?& vivi_ctrl_ops, ????????????V4L2_CID_AUDIO_VOLUME, ?0, ?255, ?1, ?200) ; ????dev- > brightness?= ?v4l2_ctrl_new_std( hdl, ?& vivi_ctrl_ops, ????????????V4L2_CID_BRIGHTNESS, ?0, ?255, ?1, ?127) ; ????dev- > contrast?= ?v4l2_ctrl_new_std( hdl, ?& vivi_ctrl_ops, ????????????V4L2_CID_CONTRAST, ?0, ?255, ?1, ?16) ; ????dev- > saturation?= ?v4l2_ctrl_new_std( hdl, ?& vivi_ctrl_ops, ????????????V4L2_CID_SATURATION, ?0, ?255, ?1, ?127) ; ????dev- > hue?= ?v4l2_ctrl_new_std( hdl, ?& vivi_ctrl_ops, ????????????V4L2_CID_HUE, ?- 128, ?127, ?1, ?0) ; ????dev- > button?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_button, ?NULL ) ; ????dev- > int32?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_int32, ?NULL ) ; ????dev- > int64?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_int64, ?NULL ) ; ????dev- > boolean?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_boolean, ?NULL ) ; ????dev- > menu?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_menu, ?NULL ) ; ????dev- > string ?= ?v4l2_ctrl_new_custom( hdl, ?& vivi_ctrl_string, ?NULL ) ; ????if ?( hdl- > error ) ?{ ????????ret?= ?hdl- > error ; ????????goto unreg_dev; ????} ????dev- > v4l2_dev. ctrl_handler?= ?hdl; ????/ * ?initialize locks?* / ????spin_lock_init( & dev- > slock) ; ????/ * ?initialize queue, ?learn it later?* / ????q?= ?& dev- > vb_vidq; ????memset( q, ?0, ?sizeof( dev- > vb_vidq) ) ; ????q- > type?= ?V4L2_BUF_TYPE_VIDEO_CAPTURE; ????q- > io_modes?= ?VB2_MMAP?| ?VB2_USERPTR?| ?VB2_READ; ????q- > drv_priv?= ?dev; ????q- > buf_struct_size?= ?sizeof( struct vivi_buffer) ; ????q - > ops? = ?& vivi_video_qops ; ????q - > mem_ops? = ?& vb2_vmalloc_memops ; ????vb2_queue_init ( q ) ; ????mutex_init( & dev- > mutex) ; ????/ * ?init video dma queues?* / ????INIT_LIST_HEAD( & dev- > vidq. active) ; ????init_waitqueue_head( & dev- > vidq. wq) ; ????/ * ?before register the video_device, ?init the video_device data* / ????ret?= ?- ENOMEM; ????vfd?= ?video_device_alloc( ) ; ????if ?( ! vfd) ????????goto unreg_dev; ????* vfd?= ?vivi_template; / * ?the most important struct?* / ????vfd- > debug?= ?debug; ????vfd- > v4l2_dev?= ?& dev- > v4l2_dev; ?/ * ?here?set ?the v4l2_device, ?you have already registered it?* / ????set_bit( V4L2_FL_USE_FH_PRIO, ?& vfd- > flags) ; ????/ * ?????* ?Provide a mutex?to ?v4l2 core. ?It will be used?to ?protect ?????* ?all fops?and ?v4l2 ioctls. ?????* / ????vfd- > lock?= ?& dev- > mutex; ????ret?= ?video_register_device( vfd, ?VFL_TYPE_GRABBER, ?video_nr) ; ????if ?( ret?< ?0) ????????goto rel_vdev; ????/ * ????* ?You should pay attention?to ?this method ????* ?here you?set ?the vivi_dev into the vedio_device?for ?the later use?in ?fops ????* ?When you want?to ?use the vivi_dev, ?you use vedio_get_drvdata( ) ?to ?get ????* / ????video_set_drvdata( vfd, ?dev) ; ????/ * ?Now ?that everything?is ?fine, ?let ' s add it?to ?device list?* / ????list_add_tail( & dev- > vivi_devlist, ?& vivi_devlist) ; ????if ?( video_nr?! = ?- 1) ????????video_nr+ + ; ????dev- > vfd?= ?vfd; ????/ * ?the debug message* / ????v4l2_info( & dev- > v4l2_dev, ?"V4L2 device registered as %s\n" , ???????? video_device_node_name( vfd) ) ; ????return 0; rel_vdev: ????video_device_release( vfd) ; unreg_dev: ????v4l2_ctrl_handler_free( hdl) ; ????v4l2_device_unregister( & dev- > v4l2_dev) ; free_dev: ????kfree( dev) ; ????return ret; } vivi_create_instance 方法中主要完成以下工作; 1.首先通過(guò)v4l2_device_register() 方法注冊(cè) v4l2_device 2.ctrl_handler初始化 3.互斥鎖，自旋鎖等初始化 4.vb2_quene初始化 5.init video dma queues 6. 填充video_device，并且調(diào)用 video_register_device注冊(cè)video_device 7.把vivi_dev結(jié)構(gòu)set進(jìn)video_device中， 方便之后使用，使用 video_set_drvdata ( vfd , ?dev ) ; 8.設(shè)備信息加入的鏈表結(jié)構(gòu) 下面針對(duì)以上步驟做詳細(xì)分析: 1.首先通過(guò)v4l2_device_register() 方法注冊(cè) v4l2_device
int ?v4l2_device_register( struct device?* dev, ?struct v4l2_device?* v4l2_dev) { ????if ?( v4l2_dev?= = ?NULL ) ????????return?- EINVAL; ????INIT_LIST_HEAD( & v4l2_dev- > subdevs) ; ????spin_lock_init( & v4l2_dev- > lock) ; ????mutex_init( & v4l2_dev- > ioctl_lock) ; ????/ * ?initial the global priotity* / ????v4l2_prio_init ( & v4l2_dev - > prio ) ; ????kref_init ( & v4l2_dev - > ref ) ; ????v4l2_dev- > dev?= ?dev; ????if ?( dev?= = ?NULL ) ?{ ????????/ * ?If ?dev?= = ?NULL , ?then ?name must be filled?in ?by the caller?* / ????????WARN_ON( ! v4l2_dev- > name[ 0] ) ; ????????/ * ?Here give the caller a WARN, ?tell the caller?to ?set ?the dev* / ????????return 0; ????} ????/ * ?Set ?name?to ?driver name?+ ?device name?if ?it?is ?empty . ?* / ????if ?( ! v4l2_dev- > name[ 0] ) ????????snprintf( v4l2_dev- > name, ?sizeof( v4l2_dev- > name) , ?"%s %s" , ????????????dev- > driver- > name, ?dev_name( dev) ) ; ????/ * ?Here?is ?also very important, ?you can?get ?v4l2_device by use dev_get_drvdata* / ????if ?( ! dev_get_drvdata( dev) ) ????????dev_set_drvdata( dev, ?v4l2_dev) ; ????return 0; } EXPORT_SYMBOL_GPL( v4l2_device_register) ; 在 v4l2_device_register方法中，進(jìn)行v4l2設(shè)備優(yōu)先級(jí)的初始化，這里把v4l2_device中記錄優(yōu)先級(jí)狀態(tài)的v4l2_prio_state結(jié)構(gòu)變量 prio清空， 最后一步根據(jù)dev 結(jié)構(gòu)體決定，如果dev不為空，則這里setv4l2_device的name，并且將v4l2_device結(jié)構(gòu)set進(jìn)dev中，方便后面獲取使用 2. ctrl_handler初始化
/ * ?Initialize the handler?* / int ?v4l2_ctrl_handler_init( struct v4l2_ctrl_handler?* hdl, ???????????? unsigned nr_of_controls_hint) { ????mutex_init( & hdl- > lock) ; ????INIT_LIST_HEAD( & hdl- > ctrls) ; ????INIT_LIST_HEAD( & hdl- > ctrl_refs) ; ????hdl- > nr_of_buckets?= ?1?+ ?nr_of_controls_hint?/ ?8; ????hdl- > buckets?= ?kzalloc( sizeof( hdl- > buckets[ 0] ) ?* ?hdl- > nr_of_buckets, ????????????????????????????????GFP_KERNEL) ; ????hdl- > error ?= ?hdl- > buckets?? ?0?: ?- ENOMEM; ????return hdl- > error ; } 這里還是很有必要了解一下v4l2_ctrl_handler這個(gè)結(jié)構(gòu)體到底是干什么用的
/ * * ?struct v4l2_ctrl_handler?- ?The control handler keeps track of all the??* ?controls: ?both the controls owned by the handler?and ?those inherited ??* ?from other handlers. ??* ?@lock: ????Lock?to ?control access?to ?this handler?and ?its controls. ??* ?@ctrls: ????The list of controls owned by this handler. ??* ?@ctrl_refs: ????The list of control references. ??* ?@cached: ????The last found control reference. ?It?is ?common that the same ??* ????????control?is ?needed multiple times, ?so this?is ?a simple ??* ????????optimization. ??* ?@buckets: ????Buckets?for ?the hashing. ?Allows?for ?quick control lookup. ??* ?@nr_of_buckets: ?Total number of buckets?in ?the?array . ??* ?@error : ????The?error ?code of the first failed control addition. ??* / struct v4l2_ctrl_handler?{ ????struct mutex lock; ????struct list_head ctrls; ????struct list_head ctrl_refs; ????struct v4l2_ctrl_ref?* cached; ????struct v4l2_ctrl_ref?* * buckets; ????u16 nr_of_buckets; ????int ?error ; } ; 在v4l2_ctrl_handler_init方法中，主要通過(guò)nr_of_controls_hint變量的大小，計(jì)算nr_of_buckets，并為buckets申請(qǐng)空間，并將申請(qǐng)結(jié)果保存在error變量中，我感覺(jué)可以是用于以后方便check的 問(wèn)題點(diǎn)： 1. v4l2_ctrl_new_std 2. v4l2_ctrl_new_custom 以上兩個(gè)方法不是很理解，待以后研究 3.互斥鎖，自旋鎖等 初始化 4.vb2_quene初始化
/ * * ?* ?struct vb2_queue?- ?a videobuf queue ?* ?* ?@type: ????queue type?( see V4L2_BUF_TYPE_* ?in ?linux/ videodev2. h ?* ?@io_modes: ????supported io methods?( see vb2_io_modes enum) ?* ?@io_flags: ????additional io flags?( see vb2_fileio_flags enum) ?* ?@ops: ????driver- specific callbacks ?* ?@mem_ops: ????memory allocator specific callbacks ?* ?@drv_priv: ????driver?private ?data ?* ?@buf_struct_size: ?size of the driver- specific buffer structure; ?* ????????"0" ?indicates the driver doesn' t want?to ?use a custom buffer ?* ????????structure type, ?so sizeof( struct vb2_buffer) ?will?is ?used ?* ?* ?@memory: ????current memory type used ?* ?@bufs: ????videobuf buffer structures ?* ?@num_buffers: ?number of allocated/ used buffers ?* ?@queued_list: ?list of buffers currently queued from userspace ?* ?@queued_count: ?number of buffers owned by the driver ?* ?@done_list: ????list of buffers ready?to ?be dequeued?to ?userspace ?* ?@done_lock: ????lock?to ?protect done_list list ?* ?@done_wq: ????waitqueue?for ?processes waiting?for ?buffers ready?to ?be dequeued ?* ?@alloc_ctx: ????memory type/ allocator- specific contexts?for ?each ?plane ?* ?@streaming: ????current streaming state ?* ?@fileio: ????file io emulator internal data, ?used only?if ?emulator?is ?active ?* / struct vb2_queue?{ ????enum v4l2_buf_type????????type; ????unsigned?int ????????????io_modes; ????unsigned?int ????????????io_flags; ????const ?struct vb2_ops????????* ops; ????const ?struct vb2_mem_ops????* mem_ops; ????void????????????????* drv_priv; ????unsigned?int ????????????buf_struct_size; / * ?private : ?internal use only?* / ????enum v4l2_memory????????memory; ????struct vb2_buffer????????* bufs[ VIDEO_MAX_FRAME] ; ????unsigned?int ????????????num_buffers; ????struct list_head????????queued_list; ????atomic_t????????????queued_count; ????struct list_head????????done_list; ????spinlock_t????????????done_lock; ????wait_queue_head_t????????done_wq; ????void????????????????* alloc_ctx[ VIDEO_MAX_PLANES] ; ????unsigned?int ????????????streaming: 1; ????struct vb2_fileio_data????????* fileio; } ; 在 v4l2_ctrl_handler_init方法中，首先對(duì) vb2_quene其中的重要數(shù)據(jù)進(jìn)行填充，最最重要的就是 這兩條簡(jiǎn)單的復(fù)制語(yǔ)句責(zé)任重大啊， 這里先知道有這么一回事，后面補(bǔ)充
/ * * ?* ?struct vb2_ops?- ?driver- specific callbacks ?* ?* ?@queue_setup: ????called from a VIDIOC_REQBUFS handler, ?before ?* ????????????memory allocation; ?driver should return the required ?* ????????????number of buffers?in ?num_buffers, ?the required number ?* ????????????of planes per buffer?in ?num_planes; ?the size of?each ?* ????????????plane should be?set ?in ?the sizes[ ] ?array ?and ?optional ?* ????????????per- plane allocator specific context?in ?alloc_ctxs[ ] ?* ????????????array ?* ?@wait_prepare: ????release any locks taken?while ?calling vb2 functions; ?* ????????????it?is ?called before an ioctl needs?to ?wait?for ?a new ?* ????????????buffer?to ?arrive; ?required?to ?avoid a deadlock?in ?* ????????????blocking access type ?* ?@wait_finish: ????reacquire all locks released?in ?the previous callback; ?* ????????????required?to ?continue operation after sleeping?while ?* ????????????waiting?for ?a new buffer?to ?arrive ?* ?@buf_init: ????????called once after allocating a buffer?( in ?MMAP?case ) ?* ????????????or ?after acquiring a new USERPTR buffer; ?drivers may ?* ????????????perform additional buffer- related initialization; ?* ????????????initialization failure?( return?! = ?0) ?will prevent ?* ????????????queue setup from completing successfully; ?optional ?* ?@buf_prepare: ????called every?time ?the buffer?is ?queued from userspace; ?* ????????????drivers may perform any initialization required before ?* ????????????each ?hardware operation?in ?this callback; ?* ????????????if ?an?error ?is ?returned, ?the buffer will?not ?be queued ?* ????????????in ?driver; ?optional ?* ?@buf_finish: ????????called before every dequeue of the buffer back?to ?* ????????????userspace; ?drivers may perform any operations required ?* ????????????before userspace accesses the buffer; ?optional ?* ?@buf_cleanup: ????called once before the buffer?is ?freed; ?drivers may ?* ????????????perform any additional cleanup; ?optional ?* ?@start_streaming: ????called once before entering?' streaming' ?state; ?enables ?* ????????????driver?to ?receive buffers over buf_queue( ) ?callback ?* ?@stop_streaming: ????called when?' streaming' ?state must be disabled; ?driver ?* ????????????should stop any DMA transactions?or ?wait?until ?they ?* ????????????finish?and ?give back all buffers it got from buf_queue( ) ?* ????????????callback; ?may use vb2_wait_for_all_buffers( ) ?function ?* ?@buf_queue: ????????passes buffer vb?to ?the driver; ?driver may start ?* ????????????hardware operation?on ?this buffer; ?driver should give ?* ????????????the buffer back by calling vb2_buffer_done( ) ?function ?* / struct vb2_ops?{ ????int ?( * queue_setup) ( struct vb2_queue?* q, ?unsigned?int ?* num_buffers, ???????????? unsigned?int ?* num_planes, ?unsigned long sizes[ ] , ???????????? void?* alloc_ctxs[ ] ) ; ????void?( * wait_prepare) ( struct vb2_queue?* q) ; ????void?( * wait_finish) ( struct vb2_queue?* q) ; ????int ?( * buf_init) ( struct vb2_buffer?* vb) ; ????int ?( * buf_prepare) ( struct vb2_buffer?* vb) ; ????int ?( * buf_finish) ( struct vb2_buffer?* vb) ; ????void?( * buf_cleanup) ( struct vb2_buffer?* vb) ; ????int ?( * start_streaming) ( struct vb2_queue?* q) ; ????int ?( * stop_streaming) ( struct vb2_queue?* q) ; ????void?( * buf_queue) ( struct vb2_buffer?* vb) ; } ; ?
/ * * ?* ?struct vb2_mem_ops?- ?memory handling/ memory allocator operations ?* ?@alloc: ????allocate video memory?and , ?optionally, ?allocator?private ?data, ?* ????????return?NULL ?on ?failure?or ?a pointer?to ?allocator?private , ?* ????????per- buffer data?on ?success; ?the returned?private ?structure ?* ????????will?then ?be passed as buf_priv argument?to ?other ops?in ?this ?* ????????structure ?* ?@put: ????inform the allocator that the buffer will no longer be used; ?* ????????usually will result?in ?the allocator freeing the buffer?( if ?* ????????no other users of this buffer are present) ; ?the buf_priv ?* ????????argument?is ?the allocator?private ?per- buffer structure ?* ????????previously returned from the alloc callback ?* ?@get_userptr: ?acquire userspace memory?for ?a hardware operation; ?used?for ?* ???????? USERPTR memory types; ?vaddr?is ?the address passed?to ?the ?* ???????? videobuf layer when queuing a video buffer of USERPTR type; ?* ???????? should return an allocator?private ?per- buffer structure ?* ???????? associated with the buffer?on ?success, ?NULL ?on ?failure; ?* ???????? the returned?private ?structure will?then ?be passed as buf_priv ?* ???????? argument?to ?other ops?in ?this structure ?* ?@put_userptr: ?inform the allocator that a USERPTR buffer will no longer ?* ???????? be used ?* ?@vaddr: ????return a kernel virtual address?to ?a given memory buffer ?* ????????associated with the passed?private ?structure?or ?NULL ?if ?no ?* ????????such mapping exists ?* ?@cookie: ????return allocator specific cookie?for ?a given memory buffer ?* ????????associated with the passed?private ?structure?or ?NULL ?if ?not ?* ????????available ?* ?@num_users: ????return the current number of users of a memory buffer; ?* ????????return 1?if ?the videobuf layer?( or ?actually the driver using ?* ????????it) ?is ?the only user ?* ?@mmap: ????setup a userspace mapping?for ?a given memory buffer under ?* ????????the provided virtual memory region ?* ?* ?Required ops?for ?USERPTR types: ?get_userptr, ?put_userptr. ?* ?Required ops?for ?MMAP types: ?alloc, ?put, ?num_users, ?mmap. ?* ?Required ops?for ?read/ write access types: ?alloc, ?put, ?num_users, ?vaddr ?* / struct vb2_mem_ops?{ ????void????????* ( * alloc) ( void?* alloc_ctx, ?unsigned long size) ; ????void????????( * put) ( void?* buf_priv) ; ????void????????* ( * get_userptr) ( void?* alloc_ctx, ?unsigned long vaddr, ????????????????????unsigned long size, ?int ?write) ; ????void????????( * put_userptr) ( void?* buf_priv) ; ????void????????* ( * vaddr) ( void?* buf_priv) ; ????void????????* ( * cookie) ( void?* buf_priv) ; ????unsigned?int ????( * num_users) ( void?* buf_priv) ; ????int ????????( * mmap) ( void?* buf_priv, ?struct vm_area_struct?* vma) ; } ; 最后調(diào)用 vb2_queue_init 方法，進(jìn)行初始化
/ * * ?* ?vb2_queue_init( ) ?- ?initialize a videobuf2 queue ?* ?@q: ????????videobuf2 queue; ?this structure should be allocated?in ?driver ?* ?* ?The vb2_queue structure should be allocated by the driver. ?The driver?is ?* ?responsible of clearing it' s content?and ?setting initial values?for ?some ?* ?required entries before calling this?function . ?* ?q- > ops, ?q- > mem_ops, ?q- > type?and ?q- > io_modes are mandatory. ?Please refer ?* ?to ?the struct vb2_queue description?in ?include/ media/ videobuf2- core. h ?* ?for ?more information. ?* / int ?vb2_queue_init( struct vb2_queue?* q) { ????BUG_ON( ! q) ; ????BUG_ON( ! q- > ops) ; ????BUG_ON( ! q- > mem_ops) ; ????BUG_ON( ! q- > type) ; ????BUG_ON( ! q- > io_modes) ; ????BUG_ON( ! q- > ops- > queue_setup) ; ????BUG_ON( ! q- > ops- > buf_queue) ; ????INIT_LIST_HEAD( & q- > queued_list) ; ????INIT_LIST_HEAD( & q- > done_list) ; ????spin_lock_init( & q- > done_lock) ; ????init_waitqueue_head( & q- > done_wq) ; ????if ?( q- > buf_struct_size?= = ?0) ????????q- > buf_struct_size?= ?sizeof( struct vb2_buffer) ; ????return 0; } EXPORT_SYMBOL_GPL( vb2_queue_init) ; 這里方法很簡(jiǎn)單，只是進(jìn)行check，然后最最簡(jiǎn)單的初始化，這里不再多說(shuō)了 5. init video dma queues 6. 填充video_device，并且調(diào)用 video_register_device注冊(cè)video_device 這里終于到了重點(diǎn)了，很重要，開(kāi)始了 開(kāi)始簡(jiǎn)單，申請(qǐng)內(nèi)存空間并進(jìn)行填充，然后才真正調(diào)用用video_register_device這個(gè)方法，開(kāi)始了 但是在調(diào)用之前的這條語(yǔ)句你必須關(guān)注 vfd->v4l2_dev = &dev->v4l2_dev; 從這里也可以知道v4l2_device和video_device的注冊(cè)順序
int ?__video_register_device( struct video_device?* vdev, ?int ?type, ?int ?nr, ????????int ?warn_if_nr_in_use, ?struct module?* owner) { ????int ?i?= ?0; ????int ?ret; ????int ?minor_offset?= ?0; ????int ?minor_cnt?= ?VIDEO_NUM_DEVICES; ????const ?char?* name_base; ????/ * ?A minor value of?- 1 marks this video device as never ???? having been registered?* / ????vdev- > minor?= ?- 1; ????/ * ?the release callback MUST be present?* / ????WARN_ON( ! vdev- > release) ; ????if ?( ! vdev- > release) ????????return?- EINVAL; ????/ * ?v4l2_fh support?* / ????spin_lock_init( & vdev- > fh_lock) ; ????INIT_LIST_HEAD( & vdev- > fh_list) ; ????/ * ?Part 1: ?check device type?* / ????/ * ?after here, ?you can see videx?. . . the char device?in ?/ dev?* / ? ??//這里還是單獨(dú)說(shuō)一下吧，最終你在/dev目錄下看到的video0就是在這里決定的，大家可以知道，可不是一定名字叫video的 ????switch?( type) ?{ ????case ?VFL_TYPE_GRABBER: ????????name_base?= ?"video" ; ????????break; ????case ?VFL_TYPE_VBI: ????????name_base?= ?"vbi" ; ????????break; ????case ?VFL_TYPE_RADIO: ????????name_base?= ?"radio" ; ????????break; ????case ?VFL_TYPE_SUBDEV: ????????name_base?= ?"v4l-subdev" ; ????????break; ????default: ????????printk( KERN_ERR?"%s called with unknown type: %d\n" , ???????? __func__, ?type) ; ????????return?- EINVAL; ????} ????vdev- > vfl_type?= ?type; ????vdev- > cdev?= ?NULL ; ????if ?( vdev- > v4l2_dev) ?{ ????????if ?( vdev- > v4l2_dev- > dev) ????????? ??//這里說(shuō)明vdev和保存在v4l2_device的dev具有共同的parent，對(duì)之后sys 接口那里有用 ????????????vdev- > parent?= ?vdev- > v4l2_dev- > dev; ????????if ?( vdev- > ctrl_handler?= = ?NULL ) ????????? ??//上面初始化的 ctrl_handler 在這里要派上用處了，而且 同時(shí)指向video_device和v4l2_device的 化 ctrl_handler ????????????vdev- > ctrl_handler?= ?vdev- > v4l2_dev- > ctrl_handler; ????????/ * ?If ?the prio state pointer?is ?NULL , ?then ?use the v4l2_device ???????? prio state. ?* / ????????if ?( vdev- > prio?= = ?NULL ) ????????????//上面初始化的 prio 在這里要派上用處了，而且 同時(shí)指向video_device和v4l2_device的 化 prio ????????????vdev- > prio?= ?& vdev- > v4l2_dev- > prio; ????} ??????//從這里往下挺長(zhǎng)一段代碼是在為要申請(qǐng)的字符設(shè)備尋找一個(gè)合適的設(shè)備號(hào)，這里不去深入追究了，有時(shí)間可以可慮回來(lái)看看 ????/ * ?Part 2: ?find a free minor, ?device node number?and ?device index. ?* / #ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES ????/ * ?Keep the ranges?for ?the first four types?for ?historical ?????* ?reasons. ?????* ?Newer devices?( not ?yet?in ?place) ?should use the range ?????* ?of 128- 191?and ?just pick the first free minor there ?????* ?( new style) . ?* / ????switch?( type) ?{ ????case ?VFL_TYPE_GRABBER: ????????minor_offset?= ?0; ????????minor_cnt?= ?64; ????????break; ????case ?VFL_TYPE_RADIO: ????????minor_offset?= ?64; ????????minor_cnt?= ?64; ????????break; ????case ?VFL_TYPE_VBI: ????????minor_offset?= ?224; ????????minor_cnt?= ?32; ????????break; ????default: ????????minor_offset?= ?128; ????????minor_cnt?= ?64; ????????break; ????} #endif ????/ * ?Pick a device node number?* / ????mutex_lock( & videodev_lock) ; ????nr?= ?devnode_find( vdev, ?nr?= = ?- 1?? ?0?: ?nr, ?minor_cnt) ; ????if ?( nr?= = ?minor_cnt) ????????nr?= ?devnode_find( vdev, ?0, ?minor_cnt) ; ????if ?( nr?= = ?minor_cnt) ?{ ????????printk( KERN_ERR?"could not get a free device node number\n" ) ; ????????mutex_unlock( & videodev_lock) ; ????????return?- ENFILE; ????} #ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES ????/ * ?1- on - 1 mapping of device node number?to ?minor number?* / ????i?= ?nr; #else ????/ * ?The device node number?and ?minor numbers are independent, ?so ???? we just find the first free minor number. ?* / ????for ?( i?= ?0; ?i?< ?VIDEO_NUM_DEVICES; ?i+ + ) ????????if ?( video_device[ i] ?= = ?NULL ) ????????????break; ????if ?( i?= = ?VIDEO_NUM_DEVICES) ?{ ????????mutex_unlock( & videodev_lock) ; ????????printk( KERN_ERR?"could not get a free minor\n" ) ; ????????return?- ENFILE; ????} #endif ????vdev- > minor?= ?i?+ ?minor_offset; ????vdev- > num?= ?nr; ????devnode_set( vdev) ; ????/ * ?Should?not ?happen since we thought this minor was free?* / ????WARN_ON( video_device[ vdev- > minor] ?! = ?NULL ) ; ????vdev- > index?= ?get_index( vdev) ; ????mutex_unlock( & videodev_lock) ; ?????//上面的方法獲取到了那個(gè)合適的設(shè)備號(hào)，現(xiàn)在要開(kāi)始注冊(cè)我們的字符設(shè)備了 ????/ * ?Part 3: ?Initialize the character device?* / ????vdev- > cdev?= ?cdev_alloc( ) ; ????if ?( vdev- > cdev?= = ?NULL ) ?{ ????????ret?= ?- ENOMEM; ????????goto cleanup; ????} ????vdev- > cdev- > ops?= ?& v4l2_fops; / / most important part，操作設(shè)備的通道 ????vdev- > cdev- > owner?= ?owner; ????ret?= ?cdev_add( vdev- > cdev, ?MKDEV( VIDEO_MAJOR, ?vdev- > minor) , ?1) ; ????if ?( ret?< ?0) ?{ ????????printk( KERN_ERR?"%s: cdev_add failed\n" , ?__func__) ; ????????kfree( vdev- > cdev) ; ????????vdev- > cdev?= ?NULL ; ????????goto cleanup; ????} ?????//這里我們也大可先不用關(guān)注，主要是在sysfs的一些設(shè)備添加等等 ????/ * ?Part 4: ?register the device with sysfs?* / ????vdev- > dev. class ?= ?& video_class; ????vdev- > dev. devt?= ?MKDEV( VIDEO_MAJOR, ?vdev- > minor) ; ????if ?( vdev- > parent) ????????vdev- > dev. parent?= ?vdev- > parent; ????dev_set_name( & vdev- > dev, ?"%s%d" , ?name_base, ?vdev- > num) ; ????ret?= ?device_register( & vdev- > dev) ; ????if ?( ret?< ?0) ?{ ????????printk( KERN_ERR?"%s: device_register failed\n" , ?__func__) ; ????????goto cleanup; ????} ????/ * ?Register the release callback that will be called when the last ???? reference?to ?the device goes away. ?* / ????vdev- > dev. release?= ?v4l2_device_release; ????if ?( nr?! = ?- 1?& & ?nr?! = ?vdev- > num?& & ?warn_if_nr_in_use) ????????printk( KERN_WARNING?"%s: requested %s%d, got %s\n" , ?__func__, ????????????name_base, ?nr, ?video_device_node_name( vdev) ) ; ????/ * ?Increase v4l2_device refcount?* / ????if ?( vdev- > v4l2_dev) ????????v4l2_device_get( vdev- > v4l2_dev) ; #if ?defined( CONFIG_MEDIA_CONTROLLER) ? ? ?//這里其實(shí)還是比較重要的，不過(guò)不是所以的驅(qū)動(dòng)都要添加這一個(gè)步驟，這也是為什么有一個(gè)if?define 的原因了 ????/ * ?Part 5: ?Register the entity. ?* / ????if ?( vdev- > v4l2_dev?& & ?vdev- > v4l2_dev- > mdev?& & ???? vdev- > vfl_type?! = ?VFL_TYPE_SUBDEV) ?{ ????????vdev- > entity. type?= ?MEDIA_ENT_T_DEVNODE_V4L; ????????vdev- > entity. name?= ?vdev- > name; ????????vdev- > entity. v4l. major?= ?VIDEO_MAJOR; ????????vdev- > entity. v4l. minor?= ?vdev- > minor; ????????ret?= ?media_device_register_entity( vdev- > v4l2_dev- > mdev, ????????????& vdev- > entity) ; ????????if ?( ret?< ?0) ????????????printk( KERN_WARNING ?????????????"%s: media_device_register_entity failed\n" , ???????????? __func__) ; ????} #endif ? ??//保存注冊(cè)成功標(biāo)記，并將注冊(cè)成功的video_device保存到全局?jǐn)?shù)組video_device中，大功告成 ????/ * ?Part 6: ?Activate this minor. ?The char device can?now ?be used. ?* / ????set_bit ( V4L2_FL_REGISTERED , ?& vdev - > flags ) ;//設(shè)置標(biāo)志位，之后還會(huì)遇到test_bit方法用來(lái)check flags的第nr位是否為1. ? ? //這里還是多說(shuō)一點(diǎn)，另外還有兩中標(biāo)志位需要知道：V4L2_FL_USES_V4L2_FH，?V4L2_FL_USE_FH_PRIO ????mutex_lock( & videodev_lock) ; ????video_device[ vdev- > minor] ?= ?vdev; ????mutex_unlock( & videodev_lock) ; ????return 0; ?//這里是出錯(cuò)處理函數(shù) cleanup: ????mutex_lock( & videodev_lock) ; ????if ?( vdev- > cdev) ????????cdev_del( vdev- > cdev) ; ????devnode_clear( vdev) ; ????mutex_unlock( & videodev_lock) ; ????/ * ?Mark this video device as never having been registered. ?* / ????vdev- > minor?= ?- 1; ????return ret; } EXPORT_SYMBOL( __video_register_device) ; 7.把vivi_dev結(jié)構(gòu)set進(jìn)video_device中， 方便之后使用， 設(shè)備信息加入的鏈表結(jié)構(gòu) 最后結(jié)尾的這段代碼這里我決定單獨(dú)放在下面分析，也算妥善收尾吧
????/ * ????* ?You should pay attention?to ?this method ????* ?here you?set ?the vivi_dev into the vedio_device?for ?the later use?in ?fops ????* ?When you want?to ?use the vivi_dev, ?you use vedio_get_drvdata( ) ?to ?get ????* / ????video_set_drvdata ( vfd , ?dev ) ; ????/ * ?Now ?that everything?is ?fine, ?let ' s add it?to ?device list?* / ????l ist_add_tail ( & dev - > vivi_devlist , ?& vivi_devlist ) ;//添加的device list當(dāng)中 ????if ?( video_nr?! = ?- 1) ????????video_nr + + ;//用于計(jì)數(shù)，找到設(shè)備 ????dev - > vfd? = ?vfd ;關(guān)聯(lián)video_device和vivi_dev 短短的幾條語(yǔ)句，但我看來(lái)，個(gè)個(gè)都短小精悍 首先說(shuō)說(shuō)這個(gè)方法，他有什么用處呢？其實(shí)用處可大了，就行我上面注釋的那樣，這里把vivi_dev設(shè)置到vedio_device中，是為了之后字符設(shè)備訪(fǎng)問(wèn)接口中使用 這里多說(shuō)一點(diǎn)，也算順便說(shuō)一下用戶(hù)空間操作設(shè)備的流程了 首先當(dāng)時(shí)用戶(hù)空間訪(fǎng)問(wèn)設(shè)備了，這個(gè)做驅(qū)動(dòng)的不懂那可糗大了，用戶(hù)空間open時(shí)，也就是啟動(dòng)了上面video_device_register方法中的很重要的下面結(jié)構(gòu)中的open方法
static?const ?struct file_operations v4l2_fops?= ?{ ????. owner?= ?THIS_MODULE, ????. read?= ?v4l2_read, ????. write?= ?v4l2_write, ????. open? = ?v4l2_open , ????. get_unmapped_area?= ?v4l2_get_unmapped_area, ????. mmap?= ?v4l2_mmap, ????. unlocked_ioctl?= ?v4l2_ioctl, #ifdef CONFIG_COMPAT ????. compat_ioctl?= ?v4l2_compat_ioctl32, #endif ????. release?= ?v4l2_release, ????. poll?= ?v4l2_poll, ????. llseek?= ?no_llseek, } ; 我們來(lái)看一下這個(gè)open方法
/ * ?Override?for ?the open?function ?* / static?int ?v4l2_open( struct inode?* inode, ?struct file?* filp) { ????struct video_device?* vdev; ????int ?ret?= ?0; ????/ * ?Check?if ?the video device?is ?available?* / ????mutex_lock( & videodev_lock) ; ????vdev? = ?video_devdata ( filp ) ; ????/ * ?return ENODEV?if ?the video device has already been removed. ?* / ????if ?( vdev?= = ?NULL ?| | ?! video_is_registered( vdev) ) ?{ ????????mutex_unlock( & videodev_lock) ; ????????return?- ENODEV; ????} ????/ * ?and ?increase the device refcount?* / ????video_get( vdev) ;//這里是用來(lái)計(jì)數(shù)的 ????mutex_unlock( & videodev_lock) ; ????/ * ? ????* ?Here using the API you?get ?the method you?get ?the open( ) ?method write ????* ?The other methods?in ?fops use the same method?to ?use you own code? ????* / ????if ?( vdev- > fops- > open) ?{ ????????if ?( vdev- > lock?& & ?mutex_lock_interruptible( vdev- > lock) ) ?{ ????????????ret?= ?- ERESTARTSYS; ????????????goto?err ; ????????} ????????if ?( video_is_registered( vdev) ) ????????????ret? = ?vdev - > fops - > open ( filp ) ; ????????else ????????????ret?= ?- ENODEV; ????????if ?( vdev- > lock) ????????????mutex_unlock( vdev- > lock) ; ????} err : ????/ * ?decrease the refcount?in ?case ?of an?error ?* / ????if ?( ret) ????????video_put( vdev) ; ????return ret; } 只有最下面的那個(gè)標(biāo)準(zhǔn)才是重點(diǎn)，經(jīng)過(guò)那么多的check，最后走的了最后這一步， ret? = ?vdev - > fops - > open ( filp ) ; 這個(gè)open方法在哪里呢？那就沿著箭頭方向找吧，是video_device內(nèi)部的fops中的open方法，這個(gè)方法不是有在哪里呢？ 接著找，在 video_device_register方法之前 *vfd = vivi_template;/* the most important struct */我還特意在這里寫(xiě)了最重要的結(jié)構(gòu)體 所以最終調(diào)用的是 vivi_template 中fops中定義的open方法
static?const ?struct v4l2_file_operations vivi_fops?= ?{ ????. owner????????= ?THIS_MODULE, ????. open???????? = ?v4l2_fh_open , ????. release?= ?vivi_close, ????. read?= ?vivi_read, ????. poll????????= ?vivi_poll, ????. unlocked_ioctl?= ?video_ioctl2, ?/ * ?V4L2 ioctl handler?* / ????. mmap?= ?vivi_mmap, } ; static?const ?struct v4l2_ioctl_ops vivi_ioctl_ops?= ?{ ????. vidioc_querycap?= ?vidioc_querycap, ????. vidioc_enum_fmt_vid_cap?= ?vidioc_enum_fmt_vid_cap, ????. vidioc_g_fmt_vid_cap?= ?vidioc_g_fmt_vid_cap, ????. vidioc_try_fmt_vid_cap?= ?vidioc_try_fmt_vid_cap, ????. vidioc_s_fmt_vid_cap?= ?vidioc_s_fmt_vid_cap, ????. vidioc_reqbufs?= ?vidioc_reqbufs, ????. vidioc_querybuf?= ?vidioc_querybuf, ????. vidioc_qbuf?= ?vidioc_qbuf, ????. vidioc_dqbuf?= ?vidioc_dqbuf, ????. vidioc_s_std?= ?vidioc_s_std, ????. vidioc_enum_input?= ?vidioc_enum_input, ????. vidioc_g_input?= ?vidioc_g_input, ????. vidioc_s_input?= ?vidioc_s_input, ????. vidioc_streamon?= ?vidioc_streamon, ????. vidioc_streamoff?= ?vidioc_streamoff, } ; static struct video_device vivi_template?= ?{ ????. name????????= ?"vivi" , ????. fops? = ?& vivi_fops , ????. ioctl_ops ????= ?& vivi_ioctl_ops, ????. release????= ?video_device_release, ????. tvnorms?= ?V4L2_STD_525_60, ????. current_norm?= ?V4L2_STD_NTSC_M, } ; 我們找到了，就是 v4l2_fh_open 這個(gè)方法，這個(gè)方法與我們之前寫(xiě)字符驅(qū)動(dòng)時(shí)遇到的情況很是不同，他的open方法其實(shí)是有內(nèi)核API寫(xiě)好的，我們先看看
int ?v4l2_fh_open( struct file?* filp) { ????struct video_device?* vdev?= ?video_devdata( filp) ; ????struct v4l2_fh?* fh?= ?kzalloc( sizeof( * fh) , ?GFP_KERNEL) ; ????/ * ????* ?IN ?the open method, ?do ?only one job ????* ?set ?v4l2_fh into filp- > private_data?for ?later use, ?and ?initial v4l2_fh ????* / ????filp- > private_data?= ?fh; ????if ?( fh?= = ?NULL ) ????????return?- ENOMEM; ????v4l2_fh_init( fh, ?vdev) ; ????v4l2_fh_add( fh) ; ????return 0; } EXPORT_SYMBOL_GPL( v4l2_fh_open) ; 這個(gè)open方法將v4l2_fh 這個(gè)同樣很重要的結(jié)構(gòu)體保存到filp->private中，并做一些初始化，具體過(guò)程暫且不說(shuō) 這里fops中的其他接口的實(shí)現(xiàn)比起open，方法是一樣的，而且更簡(jiǎn)單 但是，這里我真正想表達(dá)的東西還沒(méi)有出現(xiàn)，大家看到這里的 filp - > private_data? = ?fh ;//問(wèn)題就在這里了，我們真正在read，write中需要傳遞的想要使用的是vivi_dev其實(shí)， vivi_template 中fops中 定義的read方法吧
static ssize_t vivi_read( struct file?* file, ?char __user?* data, ?size_t count, ?loff_t?* ppos) { ????struct vivi_dev?* dev?= ?video_drvdata( file) ; ????dprintk( dev, ?1, ?"read called\n" ) ; ????return vb2_read( & dev- > vb_vidq, ?data, ?count, ?ppos, ???????? file- > f_flags?& ?O_NONBLOCK) ; } 這里大家看到了，方法獲取到vivi_dev這個(gè)數(shù)據(jù)結(jié)構(gòu)，并傳遞到vb2_read這個(gè)方法中，這個(gè)方法時(shí)驅(qū)動(dòng)中數(shù)據(jù)傳輸?shù)年P(guān)鍵，之后再慢慢研究，這里同樣不深究 而這個(gè)vivi_dev是通過(guò)video_drvdata方法獲得的，這就是為什么在上面我強(qiáng)調(diào)的要用 video_set_drvdata ( vfd , ?dev ) ; 把vivi_dev裝載到video_device中 到這里基本的過(guò)程都整理完了，其實(shí)大頭還在后面呢，待續(xù)。。。。。。
轉(zhuǎn)載于:https://www.cnblogs.com/jiangu66/archive/2013/04/23/3037421.html
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