1.14. V4L2 videobuf2 functions and data structures¶
-
enum
vb2_memory
¶ type of memory model used to make the buffers visible on userspace.
Constants
VB2_MEMORY_UNKNOWN
- Buffer status is unknown or it is not used yet on userspace.
VB2_MEMORY_MMAP
- The buffers are allocated by the Kernel and it is memory mapped via mmap() ioctl. This model is also used when the user is using the buffers via read() or write() system calls.
VB2_MEMORY_USERPTR
- The buffers was allocated in userspace and it is memory mapped via mmap() ioctl.
VB2_MEMORY_DMABUF
- The buffers are passed to userspace via DMA buffer.
-
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
alloc
- allocate video memory and, optionally, allocator private data, return ERR_PTR() 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. The size argument to this function shall be page aligned.
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_dmabuf
- acquire userspace memory for a hardware operation; used for DMABUF memory types.
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, ERR_PTR() 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.
prepare
- called every time the buffer is passed from userspace to the driver, useful for cache synchronisation, optional.
finish
- called every time the buffer is passed back from the driver to the userspace, also optional.
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 ERR_PTR() on failure; allocator private per-buffer structure on success; this needs to be used for further accesses to the buffer. 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.
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.
unmap_dmabuf
- releases access control to the dmabuf - allocator is notified that this driver is done using the dmabuf for now.
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.
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 {
unsigned int offset;
unsigned long userptr;
int fd;
} m;
unsigned int data_offset;
};
Members
mem_priv
- private data with this plane.
dbuf
- dma_buf - shared buffer object.
dbuf_mapped
- flag to show whether dbuf is mapped or not
bytesused
- number of bytes occupied by data in the plane (payload).
length
- size of this plane (NOT the payload) in bytes.
min_length
- minimum required size of this plane (NOT the payload) in bytes. length is always greater or equal to min_length.
m
- Union with memtype-specific data.
m.offset
- when memory in the associated struct vb2_buffer is
VB2_MEMORY_MMAP
, equals the offset from the start of the device memory for this plane (or is a "cookie" that should be passed to mmap() called on the video node). m.userptr
- when memory is
VB2_MEMORY_USERPTR
, a userspace pointer pointing to this plane. m.fd
- when memory is
VB2_MEMORY_DMABUF
, a userspace file descriptor associated with this plane. data_offset
- offset in the plane to the start of data; usually 0, unless there is a header in front of the data.
Description
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_IN_REQUEST
- buffer is queued in media request.
VB2_BUF_STATE_PREPARING
- buffer is being prepared in videobuf.
VB2_BUF_STATE_QUEUED
- buffer queued in videobuf, but not in 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;
u64 timestamp;
struct media_request *request;
struct media_request_object req_obj;
};
Members
vb2_queue
- pointer to
struct vb2_queue
with the queue to which this driver belongs. index
- id number of the buffer.
type
- buffer type.
memory
- the method, in which the actual data is passed.
num_planes
- number of planes in the buffer on an internal driver queue.
timestamp
- frame timestamp in ns.
request
- the request this buffer is associated with.
req_obj
- used to bind this buffer to a request. This request object has a refcount.
-
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_out_validate)(struct vb2_buffer *vb);
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);
void (*buf_request_complete)(struct vb2_buffer *vb);
};
Members
queue_setup
- called from
VIDIOC_REQBUFS()
andVIDIOC_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 fromVIDIOC_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 fromVIDIOC_CREATE_BUFS()
, *num_planes != 0 and it describes the requested number of planes and sizes[] contains the requested plane sizes. In this case *num_buffers are being allocated additionally to q->num_buffers. If either *num_planes or the requested sizes are invalid callback must return-EINVAL
. 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_out_validate
- called when the output buffer is prepared or queued to a request; drivers can use this to validate userspace-provided information; this is required only for OUTPUT queues.
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
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 supportVIDIOC_CREATE_BUFS()
must also validate the buffer size; 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; 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
andERROR
occur while streaming is in progress, and thePREPARED
state occurs when the queue has been canceled and all pending buffers are being returned to their defaultDEQUEUED
state. Typically you only have to do something if the state isVB2_BUF_STATE_DONE
, since in all other cases the buffer contents will be ignored anyway. buf_cleanup
- called once before the buffer is freed; drivers may perform any additional cleanup; optional.
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()
withVB2_BUF_STATE_QUEUED
. If you need a minimum number of buffers before you can start streaming, then setvb2_queue->min_buffers_needed
. If that is non-zero then start_streaming won't be called until at least that many buffers have been queued up by userspace. 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 callingvb2_buffer_done()
with eitherVB2_BUF_STATE_DONE
orVB2_BUF_STATE_ERROR
; may usevb2_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; it is always called after callingVIDIOC_STREAMON()
ioctl; might be called before start_streaming callback if user pre-queued buffers before callingVIDIOC_STREAMON()
. buf_request_complete
- a buffer that was never queued to the driver but is associated with a queued request was canceled. The driver will have to mark associated objects in the request as completed; required if requests are supported.
Description
These operations are not called from interrupt context except where mentioned specifically.
-
struct
vb2_buf_ops
¶ driver-specific callbacks.
Definition
struct vb2_buf_ops {
int (*verify_planes_array)(struct vb2_buffer *vb, const void *pb);
void (*init_buffer)(struct vb2_buffer *vb);
void (*fill_user_buffer)(struct vb2_buffer *vb, void *pb);
int (*fill_vb2_buffer)(struct vb2_buffer *vb, struct vb2_plane *planes);
void (*copy_timestamp)(struct vb2_buffer *vb, const void *pb);
};
Members
verify_planes_array
- Verify that a given user space structure contains enough planes for the buffer. This is called for each dequeued buffer.
init_buffer
- given a
vb2_buffer
initialize the extra data after struct vb2_buffer. For V4L2 this is astruct vb2_v4l2_buffer
. fill_user_buffer
- given a
vb2_buffer
fill in the userspace structure. For V4L2 this is astruct v4l2_buffer
. 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. copy_timestamp
- copy the timestamp from a userspace structure to
the
struct vb2_buffer
.
-
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 bidirectional:1;
unsigned fileio_read_once:1;
unsigned fileio_write_immediately:1;
unsigned allow_zero_bytesused:1;
unsigned quirk_poll_must_check_waiting_for_buffers:1;
unsigned supports_requests:1;
unsigned requires_requests:1;
unsigned uses_qbuf:1;
unsigned uses_requests: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;
u32 subsystem_flags;
unsigned int buf_struct_size;
u32 timestamp_flags;
gfp_t gfp_flags;
u32 min_buffers_needed;
struct device *alloc_devs[VB2_MAX_PLANES];
};
Members
type
- private buffer type whose content is defined by the vb2-core
caller. For example, for V4L2, it should match
the types defined on
enum v4l2_buf_type
. io_modes
- supported io methods (see
enum vb2_io_modes
). dev
- device to use for the default allocation context if the driver doesn't fill in the alloc_devs array.
dma_attrs
- DMA attributes to use for the DMA.
bidirectional
- when this flag is set the DMA direction for the buffers of
this queue will be overridden with
DMA_BIDIRECTIONAL
direction. This is useful in cases where the hardware (firmware) writes to a buffer which is mapped as read (DMA_TO_DEVICE
), or reads from buffer which is mapped for write (DMA_FROM_DEVICE
) in order to satisfy some internal hardware restrictions or adds a padding needed by the processing algorithm. In case the DMA mapping is not bidirectional but the hardware (firmware) trying to access the buffer (in the opposite direction) this could lead to an IOMMU protection faults. fileio_read_once
- report EOF after reading the first buffer
fileio_write_immediately
- queue buffer after each write() call
allow_zero_bytesused
- allow bytesused == 0 to be passed to the driver
quirk_poll_must_check_waiting_for_buffers
- Return
EPOLLERR
at poll when QBUF has not been called. This is a vb1 idiom that has been adopted also by vb2. supports_requests
- this queue supports the Request API.
requires_requests
- this queue requires the Request API. If this is set to 1, then supports_requests must be set to 1 as well.
uses_qbuf
- qbuf was used directly for this queue. Set to 1 the first time this is called. Set to 0 when the queue is canceled. If this is 1, then you cannot queue buffers from a request.
uses_requests
- requests are used for this queue. Set to 1 the first time a request is queued. Set to 0 when the queue is canceled. If this is 1, then you cannot queue buffers directly.
lock
- pointer to a mutex that protects the
struct vb2_queue
. 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. 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.
ops
- driver-specific callbacks
mem_ops
- memory allocator specific callbacks
buf_ops
- callbacks to deliver buffer information. between user-space and kernel-space.
drv_priv
- driver private data.
subsystem_flags
- Flags specific to the subsystem (V4L2/DVB/etc.). Not used by the vb2 core.
buf_struct_size
- size of the driver-specific buffer structure;
"0" indicates the driver doesn't want to use a custom buffer
structure type. In that case a subsystem-specific struct
will be used (in the case of V4L2 that is
sizeof(struct vb2_v4l2_buffer)
). The first field of the driver-specific buffer structure must be the subsystem-specific struct (vb2_v4l2_buffer in the case of V4L2). timestamp_flags
- Timestamp flags;
V4L2_BUF_FLAG_TIMESTAMP_*
andV4L2_BUF_FLAG_TSTAMP_SRC_*
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. 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.
alloc_devs
struct device
memory type/allocator-specific per-plane device
-
void *
vb2_plane_vaddr
(struct vb2_buffer * vb, unsigned int plane_no)¶ Return a kernel virtual address of a given plane.
Parameters
struct vb2_buffer * vb
- pointer to
struct vb2_buffer
to which the plane in question belongs to. unsigned int plane_no
- plane number for which the address is to be returned.
Description
This function returns a kernel virtual address of a given plane if such a mapping exist, NULL otherwise.
Return allocator specific cookie for the given plane.
Parameters
struct vb2_buffer * vb
- pointer to
struct vb2_buffer
to which the plane in question belongs to. unsigned int plane_no
- plane number for which the cookie is to be returned.
Description
This function returns an allocator specific cookie for a given plane if available, NULL otherwise. The allocator should provide some simple static inline function, which would convert this cookie to the allocator specific type that can be used directly by the driver to access the buffer. This can be for example physical address, pointer to scatter list or IOMMU mapping.
-
void
vb2_buffer_done
(struct vb2_buffer * vb, enum vb2_buffer_state state)¶ inform videobuf that an operation on a buffer is finished.
Parameters
struct vb2_buffer * vb
- pointer to
struct vb2_buffer
to be used. enum vb2_buffer_state state
- state of the buffer, as defined by
enum vb2_buffer_state
. EitherVB2_BUF_STATE_DONE
if the operation finished successfully,VB2_BUF_STATE_ERROR
if the operation finished with an error orVB2_BUF_STATE_QUEUED
.
Description
This function should be called by the driver after a hardware operation on
a buffer is finished and the buffer may be returned to userspace. The driver
cannot use this buffer anymore until it is queued back to it by videobuf
by the means of vb2_ops->buf_queue
callback. Only buffers previously queued
to the driver by vb2_ops->buf_queue
can be passed to this function.
While streaming a buffer can only be returned in state DONE or ERROR.
The vb2_ops->start_streaming
op can also return them in case the DMA engine
cannot be started for some reason. In that case the buffers should be
returned with state QUEUED to put them back into the queue.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
This function is intended to be used with suspend/resume operations. It discards all 'done' buffers as they would be too old to be requested after resume.
Drivers must stop the hardware and synchronize with interrupt handlers and/or delayed works before calling this function to make sure no buffer will be touched by the driver and/or hardware.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
This function will wait until all buffers that have been given to the driver
by vb2_ops->buf_queue
are given back to vb2 with vb2_buffer_done()
. It
doesn't call vb2_ops->wait_prepare
/vb2_ops->wait_finish
pair.
It is intended to be called with all locks taken, for example from
vb2_ops->stop_streaming
callback.
-
void
vb2_core_querybuf
(struct vb2_queue * q, unsigned int index, void * pb)¶ query video buffer information.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. unsigned int index
- id number of the buffer.
void * pb
- buffer struct passed from userspace.
Description
Videobuf2 core helper to implement VIDIOC_QUERYBUF()
operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
The passed buffer should have been verified.
This function fills the relevant information for the userspace.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_reqbufs
(struct vb2_queue * q, enum vb2_memory memory, unsigned int * count)¶ Initiate streaming.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. enum vb2_memory memory
- memory type, as defined by
enum vb2_memory
. unsigned int * count
- requested buffer count.
Description
Videobuf2 core helper to implement VIDIOC_REQBUF() operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
This function:
- verifies streaming parameters passed from the userspace;
- sets up the queue;
- negotiates number of buffers and planes per buffer with the driver to be used during streaming;
- allocates internal buffer structures (
struct vb2_buffer
), according to the agreed parameters; - for MMAP memory type, allocates actual video memory, using the memory handling/allocation routines provided during queue initialization.
If req->count is 0, all the memory will be freed instead.
If the queue has been allocated previously by a previous vb2_core_reqbufs()
call and the queue is not busy, memory will be reallocated.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_create_bufs
(struct vb2_queue * q, enum vb2_memory memory, unsigned int * count, unsigned int requested_planes, const unsigned int requested_sizes)¶ Allocate buffers and any required auxiliary structs
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. enum vb2_memory memory
- memory type, as defined by
enum vb2_memory
. unsigned int * count
- requested buffer count.
unsigned int requested_planes
- number of planes requested.
const unsigned int requested_sizes
- array with the size of the planes.
Description
Videobuf2 core helper to implement VIDIOC_CREATE_BUFS()
operation. It is
called internally by VB2 by an API-specific handler, like
videobuf2-v4l2.h
.
This function:
- verifies parameter sanity;
- calls the
vb2_ops->queue_setup
queue operation; - performs any necessary memory allocations.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_prepare_buf
(struct vb2_queue * q, unsigned int index, void * pb)¶ Pass ownership of a buffer from userspace to the kernel.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. unsigned int index
- id number of the buffer.
void * pb
- buffer structure passed from userspace to
v4l2_ioctl_ops->vidioc_prepare_buf
handler in driver.
Description
Videobuf2 core helper to implement VIDIOC_PREPARE_BUF()
operation. It is
called internally by VB2 by an API-specific handler, like
videobuf2-v4l2.h
.
The passed buffer should have been verified.
This function calls vb2_ops->buf_prepare callback in the driver (if provided), in which driver-specific buffer initialization can be performed.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_qbuf
(struct vb2_queue * q, unsigned int index, void * pb, struct media_request * req)¶ Queue a buffer from userspace
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. unsigned int index
- id number of the buffer
void * pb
- buffer structure passed from userspace to v4l2_ioctl_ops->vidioc_qbuf handler in driver
struct media_request * req
- pointer to
struct media_request
, may be NULL.
Description
Videobuf2 core helper to implement VIDIOC_QBUF()
operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
This function:
- If req is non-NULL, then the buffer will be bound to this media request and it returns. The buffer will be prepared and queued to the driver (i.e. the next two steps) when the request itself is queued.
- if necessary, calls
vb2_ops->buf_prepare
callback in the driver (if provided), in which driver-specific buffer initialization can be performed; - if streaming is on, queues the buffer in driver by the means of
vb2_ops->buf_queue
callback for processing.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_dqbuf
(struct vb2_queue * q, unsigned int * pindex, void * pb, bool nonblocking)¶ Dequeue a buffer to the userspace
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue unsigned int * pindex
- pointer to the buffer index. May be NULL
void * pb
- buffer structure passed from userspace to v4l2_ioctl_ops->vidioc_dqbuf handler in driver.
bool nonblocking
- if true, this call will not sleep waiting for a buffer if no buffers ready for dequeuing are present. Normally the driver would be passing (file->f_flags & O_NONBLOCK) here.
Description
Videobuf2 core helper to implement VIDIOC_DQBUF()
operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
This function:
- calls buf_finish callback in the driver (if provided), in which driver can perform any additional operations that may be required before returning the buffer to userspace, such as cache sync,
- the buffer struct members are filled with relevant information for the userspace.
Return
returns zero on success; an error code otherwise.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue unsigned int type
- type of the queue to be started.
For V4L2, this is defined by
enum v4l2_buf_type
type.
Description
Videobuf2 core helper to implement VIDIOC_STREAMON()
operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
Return
returns zero on success; an error code otherwise.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue unsigned int type
- type of the queue to be started.
For V4L2, this is defined by
enum v4l2_buf_type
type.
Description
Videobuf2 core helper to implement VIDIOC_STREAMOFF()
operation. It is
called internally by VB2 by an API-specific handler, like
videobuf2-v4l2.h
.
Return
returns zero on success; an error code otherwise.
-
int
vb2_core_expbuf
(struct vb2_queue * q, int * fd, unsigned int type, unsigned int index, unsigned int plane, unsigned int flags)¶ Export a buffer as a file descriptor.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. int * fd
- pointer to the file descriptor associated with DMABUF (set by driver).
unsigned int type
- buffer type.
unsigned int index
- id number of the buffer.
unsigned int plane
- index of the plane to be exported, 0 for single plane queues
unsigned int flags
- file flags for newly created file, as defined at
include/uapi/asm-generic/fcntl.h.
Currently, the only used flag is
O_CLOEXEC
. is supported, refer to manual of open syscall for more details.
Description
Videobuf2 core helper to implement VIDIOC_EXPBUF()
operation. It is called
internally by VB2 by an API-specific handler, like videobuf2-v4l2.h
.
Return
returns zero on success; an error code otherwise.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. This structure should be allocated in driver
Description
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.
Note
The following fields at q should be set before calling this function:
vb2_queue->ops
, vb2_queue->mem_ops
, vb2_queue->type
.
-
void
vb2_core_queue_release
(struct vb2_queue * q)¶ stop streaming, release the queue and free memory
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
This function stops streaming and performs necessary clean ups, including
freeing video buffer memory. The driver is responsible for freeing
the struct vb2_queue
itself.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
Flag that a fatal unrecoverable error has occurred and wake up all processes
waiting on the queue. Polling will now set EPOLLERR
and queuing and dequeuing
buffers will return -EIO
.
The error flag will be cleared when canceling the queue, either from
vb2_streamoff()
or vb2_queue_release()
. Drivers should thus not call this
function before starting the stream, otherwise the error flag will remain set
until the queue is released when closing the device node.
-
int
vb2_mmap
(struct vb2_queue * q, struct vm_area_struct * vma)¶ map video buffers into application address space.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct vm_area_struct * vma
- pointer to
struct vm_area_struct
with the vma passed to the mmap file operation handler in the driver.
Description
Should be called from mmap file operation handler of a driver. This function maps one plane of one of the available video buffers to userspace. To map whole video memory allocated on reqbufs, this function has to be called once per each plane per each buffer previously allocated.
When the userspace application calls mmap, it passes to it an offset returned
to it earlier by the means of v4l2_ioctl_ops->vidioc_querybuf
handler.
That offset acts as a "cookie", which is then used to identify the plane
to be mapped.
This function finds a plane with a matching offset and a mapping is performed by the means of a provided memory operation.
The return values from this function are intended to be directly returned from the mmap handler in driver.
-
unsigned long
vb2_get_unmapped_area
(struct vb2_queue * q, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)¶ map video buffers into application address space.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. unsigned long addr
- memory address.
unsigned long len
- buffer size.
unsigned long pgoff
- page offset.
unsigned long flags
- memory flags.
Description
This function is used in noMMU platforms to propose address mapping
for a given buffer. It's intended to be used as a handler for the
file_operations->get_unmapped_area
operation.
This is called by the mmap() syscall routines will call this
to get a proposed address for the mapping, when !CONFIG_MMU
.
-
__poll_t
vb2_core_poll
(struct vb2_queue * q, struct file * file, poll_table * wait)¶ implements poll syscall() logic.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct file * file
struct file
argument passed to the poll file operation handler.poll_table * wait
poll_table
wait argument passed to the poll file operation handler.
Description
This function implements poll file operation handler for a driver. For CAPTURE queues, if a buffer is ready to be dequeued, the userspace will be informed that the file descriptor of a video device is available for reading. For OUTPUT queues, if a buffer is ready to be dequeued, the file descriptor will be reported as available for writing.
The return values from this function are intended to be directly returned from poll handler in driver.
-
size_t
vb2_read
(struct vb2_queue * q, char __user * data, size_t count, loff_t * ppos, int nonblock)¶ implements read() syscall logic.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. char __user * data
- pointed to target userspace buffer
size_t count
- number of bytes to read
loff_t * ppos
- file handle position tracking pointer
int nonblock
- mode selector (1 means blocking calls, 0 means nonblocking)
-
size_t
vb2_write
(struct vb2_queue * q, const char __user * data, size_t count, loff_t * ppos, int nonblock)¶ implements write() syscall logic.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. const char __user * data
- pointed to target userspace buffer
size_t count
- number of bytes to write
loff_t * ppos
- file handle position tracking pointer
int nonblock
- mode selector (1 means blocking calls, 0 means nonblocking)
-
vb2_thread_fnc
¶ Typedef: callback function for use with vb2_thread.
Syntax
int vb2_thread_fnc (struct vb2_buffer * vb, void * priv);
Parameters
struct vb2_buffer * vb
- pointer to struct
vb2_buffer
. void * priv
- pointer to a private data.
Description
This is called whenever a buffer is dequeued in the thread.
-
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
- pointer to
struct vb2_queue
with videobuf2 queue. vb2_thread_fnc fnc
vb2_thread_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.
Attention
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 mailing list first.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 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 vb2_ops->queue_setup
op and reject it if this function returns
true.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 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
- pointer to
struct vb2_queue
with videobuf2 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
- pointer to
struct vb2_buffer
to which the plane in question belongs to. 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
- pointer to
struct vb2_buffer
to which the plane in question belongs to. 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
- pointer to
struct vb2_buffer
to which the plane in question belongs to. unsigned int plane_no
- plane number for which size should be returned.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
-
void
vb2_clear_last_buffer_dequeued
(struct vb2_queue * q)¶ clear last buffer dequeued flag of queue.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
-
struct vb2_buffer *
vb2_get_buffer
(struct vb2_queue * q, unsigned int index)¶ get a buffer from a queue
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. unsigned int index
- buffer index
Description
This function obtains a buffer from a queue, by its index. Keep in mind that there is no refcounting involved in this operation, so the buffer lifetime should be taken into consideration.
-
bool
vb2_buffer_in_use
(struct vb2_queue * q, struct vb2_buffer * vb)¶ return true if the buffer is in use and the queue cannot be freed (by the means of VIDIOC_REQBUFS(0)) call.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct vb2_buffer * vb
- buffer for which plane size should be returned.
-
int
vb2_verify_memory_type
(struct vb2_queue * q, enum vb2_memory memory, unsigned int type)¶ Check whether the memory type and buffer type passed to a buffer operation are compatible with the queue.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. enum vb2_memory memory
- memory model, as defined by enum
vb2_memory
. unsigned int type
- private buffer type whose content is defined by the vb2-core
caller. For example, for V4L2, it should match
the types defined on enum
v4l2_buf_type
.
-
bool
vb2_request_object_is_buffer
(struct media_request_object * obj)¶ return true if the object is a buffer
Parameters
struct media_request_object * obj
- the request object.
-
unsigned int
vb2_request_buffer_cnt
(struct media_request * req)¶ return the number of buffers in the request
Parameters
struct media_request * req
- the request.
-
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;
__s32 request_fd;
bool is_held;
struct vb2_plane planes[VB2_MAX_PLANES];
};
Members
vb2_buf
- embedded struct
vb2_buffer
. flags
- buffer informational flags.
field
- field order of the image in the buffer, as defined by
enum v4l2_field
. timecode
- frame timecode.
sequence
- sequence count of this frame.
request_fd
- the request_fd associated with this buffer
is_held
- if true, then this capture buffer was held
planes
- plane information (userptr/fd, length, bytesused, data_offset).
Description
Should contain enough information to be able to cover all the fields
of struct v4l2_buffer
at videodev2.h
.
-
int
vb2_find_timestamp
(const struct vb2_queue * q, u64 timestamp, unsigned int start_idx)¶ Find buffer with given timestamp in the queue
Parameters
const struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. u64 timestamp
- the timestamp to find.
unsigned int start_idx
- the start index (usually 0) in the buffer array to start searching from. Note that there may be multiple buffers with the same timestamp value, so you can restart the search by setting start_idx to the previously found index + 1.
Description
Returns the buffer index of the buffer with the given timestamp, or -1 if no buffer with timestamp was found.
-
int
vb2_reqbufs
(struct vb2_queue * q, struct v4l2_requestbuffers * req)¶ Wrapper for
vb2_core_reqbufs()
that also verifies the memory and type values.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct v4l2_requestbuffers * req
struct v4l2_requestbuffers
passed from userspace tov4l2_ioctl_ops->vidioc_reqbufs
handler in driver.
-
int
vb2_create_bufs
(struct vb2_queue * q, struct v4l2_create_buffers * create)¶ Wrapper for
vb2_core_create_bufs()
that also verifies the memory and type values.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct v4l2_create_buffers * create
- creation parameters, passed from userspace to
v4l2_ioctl_ops->vidioc_create_bufs
handler in driver
-
int
vb2_prepare_buf
(struct vb2_queue * q, struct media_device * mdev, struct v4l2_buffer * b)¶ Pass ownership of a buffer from userspace to the kernel
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct media_device * mdev
- pointer to
struct media_device
, may be NULL. struct v4l2_buffer * b
- buffer structure passed from userspace to
v4l2_ioctl_ops->vidioc_prepare_buf
handler in driver
Description
Should be called from v4l2_ioctl_ops->vidioc_prepare_buf
ioctl handler
of a driver.
This function:
- verifies the passed buffer,
- calls
vb2_ops->buf_prepare
callback in the driver (if provided), in which driver-specific buffer initialization can be performed. - if b->request_fd is non-zero and mdev->ops->req_queue is set, then bind the prepared buffer to the request.
The return values from this function are intended to be directly returned
from v4l2_ioctl_ops->vidioc_prepare_buf
handler in driver.
-
int
vb2_qbuf
(struct vb2_queue * q, struct media_device * mdev, struct v4l2_buffer * b)¶ Queue a buffer from userspace
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct media_device * mdev
- pointer to
struct media_device
, may be NULL. struct v4l2_buffer * b
- buffer structure passed from userspace to
v4l2_ioctl_ops->vidioc_qbuf
handler in driver
Description
Should be called from v4l2_ioctl_ops->vidioc_qbuf
handler of a driver.
This function:
- verifies the passed buffer;
- if b->request_fd is non-zero and mdev->ops->req_queue is set, then bind the buffer to the request.
- if necessary, calls
vb2_ops->buf_prepare
callback in the driver (if provided), in which driver-specific buffer initialization can be performed; - if streaming is on, queues the buffer in driver by the means of
vb2_ops->buf_queue
callback for processing.
The return values from this function are intended to be directly returned
from v4l2_ioctl_ops->vidioc_qbuf
handler in driver.
-
int
vb2_expbuf
(struct vb2_queue * q, struct v4l2_exportbuffer * eb)¶ Export a buffer as a file descriptor
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct v4l2_exportbuffer * eb
- export buffer structure passed from userspace to
v4l2_ioctl_ops->vidioc_expbuf
handler in driver
Description
The return values from this function are intended to be directly returned
from v4l2_ioctl_ops->vidioc_expbuf
handler in driver.
-
int
vb2_dqbuf
(struct vb2_queue * q, struct v4l2_buffer * b, bool nonblocking)¶ Dequeue a buffer to the userspace
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct v4l2_buffer * b
- buffer structure passed from userspace to
v4l2_ioctl_ops->vidioc_dqbuf
handler in driver bool nonblocking
- if true, this call will not sleep waiting for a buffer if no
buffers ready for dequeuing are present. Normally the driver
would be passing (
file->f_flags
&O_NONBLOCK
) here
Description
Should be called from v4l2_ioctl_ops->vidioc_dqbuf
ioctl handler
of a driver.
This function:
- verifies the passed buffer;
- calls
vb2_ops->buf_finish
callback in the driver (if provided), in which driver can perform any additional operations that may be required before returning the buffer to userspace, such as cache sync; - the buffer struct members are filled with relevant information for the userspace.
The return values from this function are intended to be directly returned
from v4l2_ioctl_ops->vidioc_dqbuf
handler in driver.
-
int
vb2_streamon
(struct vb2_queue * q, enum v4l2_buf_type type)¶ start streaming
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. enum v4l2_buf_type type
- type argument passed from userspace to vidioc_streamon handler,
as defined by
enum v4l2_buf_type
.
Description
Should be called from v4l2_ioctl_ops->vidioc_streamon
handler of a driver.
This function:
- verifies current state
- passes any previously queued buffers to the driver and starts streaming
The return values from this function are intended to be directly returned
from v4l2_ioctl_ops->vidioc_streamon
handler in the driver.
-
int
vb2_streamoff
(struct vb2_queue * q, enum v4l2_buf_type type)¶ stop streaming
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. enum v4l2_buf_type type
- type argument passed from userspace to vidioc_streamoff handler
Description
Should be called from vidioc_streamoff handler of a driver.
This function:
- verifies current state,
- stop streaming and dequeues any queued buffers, including those previously passed to the driver (after waiting for the driver to finish).
This call can be used for pausing playback. The return values from this function are intended to be directly returned from vidioc_streamoff handler in the driver
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
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.
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue.
Description
This function stops streaming and performs necessary clean ups, including freeing video buffer memory. The driver is responsible for freeing the vb2_queue structure itself.
-
__poll_t
vb2_poll
(struct vb2_queue * q, struct file * file, poll_table * wait)¶ implements poll userspace operation
Parameters
struct vb2_queue * q
- pointer to
struct vb2_queue
with videobuf2 queue. struct file * file
- file argument passed to the poll file operation handler
poll_table * wait
- wait argument passed to the poll file operation handler
Description
This function implements poll file operation handler for a driver. For CAPTURE queues, if a buffer is ready to be dequeued, the userspace will be informed that the file descriptor of a video device is available for reading. For OUTPUT queues, if a buffer is ready to be dequeued, the file descriptor will be reported as available for writing.
If the driver uses struct v4l2_fh, then vb2_poll()
will also check for any
pending events.
The return values from this function are intended to be directly returned from poll handler in driver.
Parameters
struct vb2_queue * vq
- pointer to
struct vb2_queue
Description
..note:: only use if vq->lock is non-NULL.
Parameters
struct vb2_queue * vq
- pointer to
struct vb2_queue
Description
..note:: only use if vq->lock is non-NULL.
-
struct
vb2_vmarea_handler
¶ common vma refcount tracking handler.
Definition
struct vb2_vmarea_handler {
refcount_t *refcount;
void (*put)(void *arg);
void *arg;
};
Members
refcount
- pointer to
refcount_t
entry in the buffer. put
- callback to function that decreases buffer refcount.
arg
- argument for put callback.