3.2.16. ioctl DMX_REQBUFS¶
3.2.16.1. Name¶
DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O
Warning
this API is still experimental
3.2.16.2. Synopsis¶
-
int
ioctl
(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)¶
3.2.16.3. Arguments¶
fd
- File descriptor returned by open().
argp
- Pointer to struct
dmx_requestbuffers
.
3.2.16.4. Description¶
This ioctl is used to initiate a memory mapped or DMABUF based demux I/O.
Memory mapped buffers are located in device memory and must be allocated with this ioctl before they can be mapped into the application's address space. User buffers are allocated by applications themselves, and this ioctl is merely used to switch the driver into user pointer I/O mode and to setup some internal structures. Similarly, DMABUF buffers are allocated by applications through a device driver, and this ioctl only configures the driver into DMABUF I/O mode without performing any direct allocation.
To allocate device buffers applications initialize all fields of the
struct dmx_requestbuffers
structure. They set the count
field
to the desired number of buffers, and size
to the size of each
buffer.
When the ioctl is called with a pointer to this structure, the driver will
attempt to allocate the requested number of buffers and it stores the actual
number allocated in the count
field. The count
can be smaller than the number requested, even zero, when the driver runs out of free memory. A larger
number is also possible when the driver requires more buffers to
function correctly. The actual allocated buffer size can is returned
at size
, and can be smaller than what's requested.
When this I/O method is not supported, the ioctl returns an EOPNOTSUPP
error code.
Applications can call ioctl DMX_REQBUFS again to change the number of
buffers, however this cannot succeed when any buffers are still mapped.
A count
value of zero frees all buffers, after aborting or finishing
any DMA in progress.
3.2.16.5. 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.
- EOPNOTSUPP
- The the requested I/O method is not supported.