1.14. V4L2 videobuf2 functions and data structures¶

struct vb2_mem_ops¶: memory handling/memory allocator operations

Definition

struct vb2_mem_ops {
  void *(* alloc) (struct device *dev, unsigned long attrs,unsigned long size, enum dma_data_direction dma_dir,gfp_t gfp_flags);
  void (* put) (void *buf_priv);
  struct dma_buf *(* get_dmabuf) (void *buf_priv, unsigned long flags);
  void *(* get_userptr) (struct device *dev, unsigned long vaddr,unsigned long size,enum dma_data_direction dma_dir);
  void (* put_userptr) (void *buf_priv);
  void (* prepare) (void *buf_priv);
  void (* finish) (void *buf_priv);
  void *(* attach_dmabuf) (struct device *dev, struct dma_buf *dbuf,unsigned long size,enum dma_data_direction dma_dir);
  void (* detach_dmabuf) (void *buf_priv);
  int (* map_dmabuf) (void *buf_priv);
  void (* unmap_dmabuf) (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);
};

Members

void *(*)(struct device *dev, unsigned long attrs,unsigned long size, enum dma_data_direction dma_dir,gfp_t gfp_flags) 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. Additional gfp_flags to use when allocating the are also passed to this operation. These flags are from the gfp_flags field of vb2_queue.
void (*)(void *buf_priv) 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.
struct dma_buf *(*)(void *buf_priv, unsigned long flags) get_dmabuf: acquire userspace memory for a hardware operation; used for DMABUF memory types.
void *(*)(struct device *dev, unsigned long vaddr,unsigned long size,enum dma_data_direction dma_dir) 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.
void (*)(void *buf_priv) put_userptr: inform the allocator that a USERPTR buffer will no longer be used.
void (*)(void *buf_priv) prepare: called every time the buffer is passed from userspace to the driver, useful for cache synchronisation, optional.
void (*)(void *buf_priv) finish: called every time the buffer is passed back from the driver to the userspace, also optional.
void *(*)(struct device *dev, struct dma_buf *dbuf,unsigned long size,enum dma_data_direction dma_dir) attach_dmabuf: attach a shared struct dma_buf for a hardware operation; used for DMABUF memory types; dev is the alloc device dbuf is the shared dma_buf; returns NULL on failure; allocator private per-buffer structure on success; this needs to be used for further accesses to the buffer.
void (*)(void *buf_priv) detach_dmabuf: inform the exporter of the buffer that the current DMABUF buffer is no longer used; the buf_priv argument is the allocator private per-buffer structure previously returned from the attach_dmabuf callback.
int (*)(void *buf_priv) map_dmabuf: request for access to the dmabuf from allocator; the allocator of dmabuf is informed that this driver is going to use the dmabuf.
void (*)(void *buf_priv) unmap_dmabuf: releases access control to the dmabuf - allocator is notified that this driver is done using the dmabuf for now.
void *(*)(void *buf_priv) vaddr: return a kernel virtual address to a given memory buffer associated with the passed private structure or NULL if no such mapping exists.
void *(*)(void *buf_priv) cookie: return allocator specific cookie for a given memory buffer associated with the passed private structure or NULL if not available.
unsigned int (*)(void *buf_priv) 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.
int (*)(void *buf_priv, struct vm_area_struct *vma) mmap: setup a userspace mapping for a given memory buffer under the provided virtual memory region.

Description

Those operations are used by the videobuf2 core to implement the memory handling/memory allocators for each type of supported streaming I/O method.

Note

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.
Required ops for DMABUF types: attach_dmabuf, detach_dmabuf, map_dmabuf, unmap_dmabuf.

struct vb2_plane¶: plane information

Definition

struct vb2_plane {
  void * mem_priv;
  struct dma_buf * dbuf;
  unsigned int dbuf_mapped;
  unsigned int bytesused;
  unsigned int length;
  unsigned int min_length;
  union m;
  unsigned int data_offset;
};

Members

void * mem_priv: private data with this plane
struct dma_buf * dbuf: dma_buf - shared buffer object
unsigned int dbuf_mapped: flag to show whether dbuf is mapped or not
unsigned int bytesused: number of bytes occupied by data in the plane (payload)
unsigned int length: size of this plane (NOT the payload) in bytes
unsigned int min_length: minimum required size of this plane (NOT the payload) in bytes. length is always greater or equal to min_length.
union m: Union with memtype-specific data (offset, userptr or fd).
unsigned int data_offset: offset in the plane to the start of data; usually 0, unless there is a header in front of the data Should contain enough information to be able to cover all the fields of struct v4l2_plane at videodev2.h

enum vb2_io_modes¶: queue access methods

Constants

VB2_MMAP: driver supports MMAP with streaming API
VB2_USERPTR: driver supports USERPTR with streaming API
VB2_READ: driver supports read() style access
VB2_WRITE: driver supports write() style access
VB2_DMABUF: driver supports DMABUF with streaming API

enum vb2_buffer_state¶: current video buffer state

Constants

VB2_BUF_STATE_DEQUEUED: buffer under userspace control
VB2_BUF_STATE_PREPARING: buffer is being prepared in videobuf
VB2_BUF_STATE_PREPARED: buffer prepared in videobuf and by the driver
VB2_BUF_STATE_QUEUED: buffer queued in videobuf, but not in driver
VB2_BUF_STATE_REQUEUEING: re-queue a buffer to the driver
VB2_BUF_STATE_ACTIVE: buffer queued in driver and possibly used in a hardware operation
VB2_BUF_STATE_DONE: buffer returned from driver to videobuf, but not yet dequeued to userspace
VB2_BUF_STATE_ERROR: same as above, but the operation on the buffer has ended with an error, which will be reported to the userspace when it is dequeued

struct vb2_buffer¶: represents a video buffer

Definition

struct vb2_buffer {
  struct vb2_queue * vb2_queue;
  unsigned int index;
  unsigned int type;
  unsigned int memory;
  unsigned int num_planes;
  struct vb2_plane planes[VB2_MAX_PLANES];
  u64 timestamp;
};

Members

struct vb2_queue * vb2_queue: the queue to which this driver belongs
unsigned int index: id number of the buffer
unsigned int type: buffer type
unsigned int memory: the method, in which the actual data is passed
unsigned int num_planes: number of planes in the buffer on an internal driver queue
struct vb2_plane planes[VB2_MAX_PLANES]: private per-plane information; do not change
u64 timestamp: frame timestamp in ns

struct vb2_ops¶: driver-specific callbacks

Definition

struct vb2_ops {
  int (* queue_setup) (struct vb2_queue *q,unsigned int *num_buffers, unsigned int *num_planes,unsigned int sizes[], struct device *alloc_devs[]);
  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);
  void (* buf_finish) (struct vb2_buffer *vb);
  void (* buf_cleanup) (struct vb2_buffer *vb);
  int (* start_streaming) (struct vb2_queue *q, unsigned int count);
  void (* stop_streaming) (struct vb2_queue *q);
  void (* buf_queue) (struct vb2_buffer *vb);
};

Members

int (*)(struct vb2_queue *q,unsigned int *num_buffers, unsigned int *num_planes,unsigned int sizes[], struct device *alloc_devs[]) queue_setup: called from VIDIOC_REQBUFS and VIDIOC_CREATE_BUFS handlers before memory allocation. It can be called twice: if the original number of requested buffers could not be allocated, then it will be called a second time with the actually allocated number of buffers to verify if that is OK. The 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 device in the alloc_devs[] array. When called from VIDIOC_REQBUFS, *num_planes == 0, the driver has to use the currently configured format to determine the plane sizes and *num_buffers is the total number of buffers that are being allocated. When called from VIDIOC_CREATE_BUFS, *num_planes != 0 and it describes the requested number of planes and sizes[] contains the requested plane sizes. If either *num_planes or the requested sizes are invalid callback must return -EINVAL. In this case *num_buffers are being allocated additionally to q->num_buffers.
void (*)(struct vb2_queue *q) 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.
void (*)(struct vb2_queue *q) wait_finish: reacquire all locks released in the previous callback; required to continue operation after sleeping while waiting for a new buffer to arrive.
int (*)(struct vb2_buffer *vb) 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.
int (*)(struct vb2_buffer *vb) buf_prepare: called every time the buffer is queued from userspace and from the VIDIOC_PREPARE_BUF ioctl; drivers may perform any initialization required before each hardware operation in this callback; drivers can access/modify the buffer here as it is still synced for the CPU; drivers that support VIDIOC_CREATE_BUFS must also validate the buffer size; if an error is returned, the buffer will not be queued in driver; optional.
void (*)(struct vb2_buffer *vb) buf_finish: called before every dequeue of the buffer back to userspace; the buffer is synced for the CPU, so drivers can access/modify the buffer contents; drivers may perform any operations required before userspace accesses the buffer; optional. The buffer state can be one of the following: DONE and ERROR occur while streaming is in progress, and the PREPARED state occurs when the queue has been canceled and all pending buffers are being returned to their default DEQUEUED state. Typically you only have to do something if the state is VB2_BUF_STATE_DONE, since in all other cases the buffer contents will be ignored anyway.
void (*)(struct vb2_buffer *vb) buf_cleanup: called once before the buffer is freed; drivers may perform any additional cleanup; optional.
int (*)(struct vb2_queue *q, unsigned int count) start_streaming: called once to enter ‘streaming’ state; the driver may receive buffers with buf_queue callback before start_streaming is called; the driver gets the number of already queued buffers in count parameter; driver can return an error if hardware fails, in that case all buffers that have been already given by the buf_queue callback are to be returned by the driver by calling vb2_buffer_done(VB2_BUF_STATE_QUEUED). If you need a minimum number of buffers before you can start streaming, then set min_buffers_needed in the vb2_queue structure. If that is non-zero then start_streaming won’t be called until at least that many buffers have been queued up by userspace.
void (*)(struct vb2_queue *q) 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 by calling vb2_buffer_done() with either VB2_BUF_STATE_DONE or VB2_BUF_STATE_ERROR; may use vb2_wait_for_all_buffers() function
void (*)(struct vb2_buffer *vb) 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; it is allways called after calling VIDIOC_STREAMON ioctl; might be called before start_streaming callback if user pre-queued buffers before calling VIDIOC_STREAMON.

struct vb2_buf_ops¶: driver-specific callbacks

Definition

struct vb2_buf_ops {
  int (* verify_planes_array) (struct vb2_buffer *vb, const void *pb);
  void (* fill_user_buffer) (struct vb2_buffer *vb, void *pb);
  int (* fill_vb2_buffer) (struct vb2_buffer *vb, const void *pb,struct vb2_plane *planes);
  void (* copy_timestamp) (struct vb2_buffer *vb, const void *pb);
};

Members

int (*)(struct vb2_buffer *vb, const void *pb) verify_planes_array: Verify that a given user space structure contains enough planes for the buffer. This is called for each dequeued buffer.
void (*)(struct vb2_buffer *vb, void *pb) fill_user_buffer: given a vb2_buffer fill in the userspace structure. For V4L2 this is a struct v4l2_buffer.
int (*)(struct vb2_buffer *vb, const void *pb,struct vb2_plane *planes) fill_vb2_buffer: given a userspace structure, fill in the vb2_buffer. If the userspace structure is invalid, then this op will return an error.
void (*)(struct vb2_buffer *vb, const void *pb) copy_timestamp: copy the timestamp from a userspace structure to the vb2_buffer struct.

struct vb2_queue¶: a videobuf queue

Definition

struct vb2_queue {
  unsigned int type;
  unsigned int io_modes;
  struct device * dev;
  unsigned long dma_attrs;
  unsigned fileio_read_once:1;
  unsigned fileio_write_immediately:1;
  unsigned allow_zero_bytesused:1;
  unsigned quirk_poll_must_check_waiting_for_buffers:1;
  struct mutex * lock;
  void * owner;
  const struct vb2_ops * ops;
  const struct vb2_mem_ops * mem_ops;
  const struct vb2_buf_ops * buf_ops;
  void * drv_priv;
  unsigned int buf_struct_size;
  u32 timestamp_flags;
  gfp_t gfp_flags;
  u32 min_buffers_needed;
};

Members

unsigned int type: private buffer type whose content is defined by the vb2-core caller. For example, for V4L2, it should match the V4L2_BUF_TYPE_* in include/uapi/linux/videodev2.h
unsigned int io_modes: supported io methods (see vb2_io_modes enum)
struct device * dev: device to use for the default allocation context if the driver doesn’t fill in the alloc_devs array.
unsigned long dma_attrs: DMA attributes to use for the DMA.
unsigned:1 fileio_read_once: report EOF after reading the first buffer
unsigned:1 fileio_write_immediately: queue buffer after each write() call
unsigned:1 allow_zero_bytesused: allow bytesused == 0 to be passed to the driver
unsigned:1 quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF has not been called. This is a vb1 idiom that has been adopted also by vb2.
struct mutex * lock: pointer to a mutex that protects the vb2_queue struct. The driver can set this to a mutex to let the v4l2 core serialize the queuing ioctls. If the driver wants to handle locking itself, then this should be set to NULL. This lock is not used by the videobuf2 core API.
void * owner: The filehandle that ‘owns’ the buffers, i.e. the filehandle that called reqbufs, create_buffers or started fileio. This field is not used by the videobuf2 core API, but it allows drivers to easily associate an owner filehandle with the queue.
const struct vb2_ops * ops: driver-specific callbacks
const struct vb2_mem_ops * mem_ops: memory allocator specific callbacks
const struct vb2_buf_ops * buf_ops: callbacks to deliver buffer information between user-space and kernel-space
void * drv_priv: driver private data
unsigned int buf_struct_size: size of the driver-specific buffer structure; “0” indicates the driver doesn’t want to use a custom buffer structure type. for example, sizeof(struct vb2_v4l2_buffer) will be used for v4l2.
u32 timestamp_flags: Timestamp flags; V4L2_BUF_FLAG_TIMESTAMP_* and V4L2_BUF_FLAG_TSTAMP_SRC_*
gfp_t gfp_flags: additional gfp flags used when allocating the buffers. Typically this is 0, but it may be e.g. GFP_DMA or __GFP_DMA32 to force the buffer allocation to a specific memory zone.
u32 min_buffers_needed: the minimum number of buffers needed before start_streaming() can be called. Used when a DMA engine cannot be started unless at least this number of buffers have been queued into the driver.

int vb2_thread_start(struct vb2_queue * q, vb2_thread_fnc fnc, void * priv, const char * thread_name)¶: start a thread for the given queue.

Parameters

struct vb2_queue * q: videobuf queue
vb2_thread_fnc fnc: callback function
void * priv: priv pointer passed to the callback function
const char * thread_name: the name of the thread. This will be prefixed with “vb2-”.

Description

This starts a thread that will queue and dequeue until an error occurs or vb2_thread_stop is called.

This function should not be used for anything else but the videobuf2-dvb support. If you think you have another good use-case for this, then please contact the linux-media mailinglist first.

int vb2_thread_stop(struct vb2_queue * q)¶: stop the thread for the given queue.

Parameters

struct vb2_queue * q: videobuf queue

bool vb2_is_streaming(struct vb2_queue * q)¶: return streaming status of the queue

Parameters

struct vb2_queue * q: videobuf queue

bool vb2_fileio_is_active(struct vb2_queue * q)¶: return true if fileio is active.

Parameters

struct vb2_queue * q: videobuf queue

Description

This returns true if read() or write() is used to stream the data as opposed to stream I/O. This is almost never an important distinction, except in rare cases. One such case is that using read() or write() to stream a format using V4L2_FIELD_ALTERNATE is not allowed since there is no way you can pass the field information of each buffer to/from userspace. A driver that supports this field format should check for this in the queue_setup op and reject it if this function returns true.

bool vb2_is_busy(struct vb2_queue * q)¶: return busy status of the queue

Parameters

struct vb2_queue * q: videobuf queue

Description

This function checks if queue has any buffers allocated.

void * vb2_get_drv_priv(struct vb2_queue * q)¶: return driver private data associated with the queue

Parameters

struct vb2_queue * q: videobuf queue

void vb2_set_plane_payload(struct vb2_buffer * vb, unsigned int plane_no, unsigned long size)¶: set bytesused for the plane plane_no

Parameters

struct vb2_buffer * vb: buffer for which plane payload should be set
unsigned int plane_no: plane number for which payload should be set
unsigned long size: payload in bytes

unsigned long vb2_get_plane_payload(struct vb2_buffer * vb, unsigned int plane_no)¶: get bytesused for the plane plane_no

Parameters

struct vb2_buffer * vb: buffer for which plane payload should be set
unsigned int plane_no: plane number for which payload should be set

unsigned long vb2_plane_size(struct vb2_buffer * vb, unsigned int plane_no)¶: return plane size in bytes

Parameters

struct vb2_buffer * vb: buffer for which plane size should be returned
unsigned int plane_no: plane number for which size should be returned

bool vb2_start_streaming_called(struct vb2_queue * q)¶: return streaming status of driver

Parameters

struct vb2_queue * q: videobuf queue

void vb2_clear_last_buffer_dequeued(struct vb2_queue * q)¶: clear last buffer dequeued flag of queue

Parameters

struct vb2_queue * q: videobuf queue

struct vb2_v4l2_buffer¶: video buffer information for v4l2

Definition

struct vb2_v4l2_buffer {
  struct vb2_buffer vb2_buf;
  __u32 flags;
  __u32 field;
  struct v4l2_timecode timecode;
  __u32 sequence;
};

Members

struct vb2_buffer vb2_buf: video buffer 2
__u32 flags: buffer informational flags
__u32 field: enum v4l2_field; field order of the image in the buffer
struct v4l2_timecode timecode: frame timecode
__u32 sequence: sequence count of this frame Should contain enough information to be able to cover all the fields of struct v4l2_buffer at videodev2.h

struct vb2_vmarea_handler¶: common vma refcount tracking handler

Definition

struct vb2_vmarea_handler {
  atomic_t * refcount;
  void (* put) (void *arg);
  void * arg;
};

Members

atomic_t * refcount: pointer to refcount entry in the buffer
void (*)(void *arg) put: callback to function that decreases buffer refcount
void * arg: argument for put callback

1.14. V4L2 videobuf2 functions and data structures¶

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