3.2.19. ioctl DMX_QBUF, DMX_DQBUF¶
3.2.19.1. Name¶
DMX_QBUF - DMX_DQBUF - Exchange a buffer with the driver
Warning
this API is still experimental
3.2.19.2. Synopsis¶
-
int
ioctl
(int fd, DMX_QBUF, struct dmx_buffer *argp)¶
-
int
ioctl
(int fd, DMX_DQBUF, struct dmx_buffer *argp)¶
3.2.19.3. Arguments¶
fd
- File descriptor returned by open().
argp
- Pointer to struct
dmx_buffer
.
3.2.19.4. Description¶
Applications call the DMX_QBUF
ioctl to enqueue an empty
(capturing) or filled (output) buffer in the driver's incoming queue.
The semantics depend on the selected I/O method.
To enqueue a buffer applications set the index
field. Valid index
numbers range from zero to the number of buffers allocated with
ioctl DMX_REQBUFS (struct dmx_requestbuffers
count
) minus
one. The contents of the struct dmx_buffer
returned
by a ioctl DMX_QUERYBUF ioctl will do as well.
When DMX_QBUF
is called with a pointer to this structure, it locks the
memory pages of the buffer in physical memory, so they cannot be swapped
out to disk. Buffers remain locked until dequeued, until the
the device is closed.
Applications call the DMX_DQBUF
ioctl to dequeue a filled
(capturing) buffer from the driver's outgoing queue.
They just set the index
field with the buffer ID to be queued.
When DMX_DQBUF
is called with a pointer to struct dmx_buffer
,
the driver fills the remaining fields or returns an error code.
By default DMX_DQBUF
blocks when no buffer is in the outgoing
queue. When the O_NONBLOCK
flag was given to the
open() function, DMX_DQBUF
returns
immediately with an EAGAIN
error code when no buffer is available.
The struct dmx_buffer
structure is specified in
Buffers.
3.2.19.5. Return Value¶
On success 0 is returned, on error -1 and the errno
variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.
- EAGAIN
- Non-blocking I/O has been selected using
O_NONBLOCK
and no buffer was in the outgoing queue. - EINVAL
- The
index
is out of bounds, or no buffers have been allocated yet. - EIO
DMX_DQBUF
failed due to an internal error. Can also indicate temporary problems like signal loss or CRC errors.