This system call, used with a device name of /dev/dvb/adapter0/demux0, allocates a new filter and returns a handle which can be used for subsequent control of that filter. This call has to be made for each filter to be used, i.e. every returned file descriptor is a reference to a single filter. /dev/dvb/adapter0/dvr0 is a logical device to be used for retrieving Transport Streams for digital video recording. When reading from this device a transport stream containing the packets from all PES filters set in the corresponding demux device (/dev/dvb/adapter0/demux0) having the output set to DMX_OUT_TS_TAP. A recorded Transport Stream is replayed by writing to this device.

The significance of blocking or non-blocking mode is described in the documentation for functions where there is a difference. It does not affect the semantics of the open() call itself. A device opened in blocking mode can later be put into non-blocking mode (and vice versa) using the F_SETFL command of the fcntl system call.

int open(const char ⋆deviceName, int flags);

const char *deviceName

Name of demux device.

int flags

A bit-wise OR of the following flags:

O_RDWR read/write access

O_NONBLOCK open in non-blocking mode

(blocking mode is the default)

ENODEV

Device driver not loaded/available.

EINVAL

Invalid argument.

EMFILE

“Too many open files”, i.e. no more filters available.

ENOMEM

The driver failed to allocate enough memory.

This system call deactivates and deallocates a filter that was previously allocated via the open() call.

int close(int fd);

int fd

File descriptor returned by a previous call to open().

EBADF

fd is not a valid open file descriptor.

This system call returns filtered data, which might be section or PES data. The filtered data is transferred from the driver’s internal circular buffer to buf. The maximum amount of data to be transferred is implied by count.

When returning section data the driver always tries to return a complete single section (even though buf would provide buffer space for more data). If the size of the buffer is smaller than the section as much as possible will be returned, and the remaining data will be provided in subsequent calls.

The size of the internal buffer is 2 * 4096 bytes (the size of two maximum sized sections) by default. The size of this buffer may be changed by using the DMX_SET_BUFFER_SIZE function. If the buffer is not large enough, or if the read operations are not performed fast enough, this may result in a buffer overflow error. In this case EOVERFLOW will be returned, and the circular buffer will be emptied. This call is blocking if there is no data to return, i.e. the process will be put to sleep waiting for data, unless the O_NONBLOCK flag is specified.

Note that in order to be able to read, the filtering process has to be started by defining either a section or a PES filter by means of the ioctl functions, and then starting the filtering process via the DMX_START ioctl function or by setting the DMX_IMMEDIATE_START flag. If the reading is done from a logical DVR demux device, the data will constitute a Transport Stream including the packets from all PES filters in the corresponding demux device /dev/dvb/adapter0/demux0 having the output set to DMX_OUT_TS_TAP.

size_t read(int fd, void ⋆buf, size_t count);

int fd

File descriptor returned by a previous call to open().

void *buf

Pointer to the buffer to be used for returned filtered data.

size_t count

Size of buf.

EWOULDBLOCK

No data to return and O_NONBLOCK was specified.

EBADF

fd is not a valid open file descriptor.

ECRC

Last section had a CRC error - no data returned. The buffer is flushed.

EOVERFLOW

The filtered data was not read from the buffer in due time, resulting in non-read data being lost. The buffer is flushed.

ETIMEDOUT

The section was not loaded within the stated timeout period. See ioctl DMX_SET_FILTER for how to set a timeout.

EFAULT

The driver failed to write to the callers buffer due to an invalid *buf pointer.

This system call is only provided by the logical device /dev/dvb/adapter0/dvr0, associated with the physical demux device that provides the actual DVR functionality. It is used for replay of a digitally recorded Transport Stream. Matching filters have to be defined in the corresponding physical demux device, /dev/dvb/adapter0/demux0. The amount of data to be transferred is implied by count.

ssize_t write(int fd, const void ⋆buf, size_t count);

int fd

File descriptor returned by a previous call to open().

void *buf

Pointer to the buffer containing the Transport Stream.

size_t count

Size of buf.

EWOULDBLOCK

No data was written. This might happen if O_NONBLOCK was specified and there is no more buffer space available (if O_NONBLOCK is not specified the function will block until buffer space is available).

EBUSY

This error code indicates that there are conflicting requests. The corresponding demux device is setup to receive data from the front- end. Make sure that these filters are stopped and that the filters with input set to DMX_IN_DVR are started.

EBADF

fd is not a valid open file descriptor.

This ioctl call is used to start the actual filtering operation defined via the ioctl calls DMX_SET_FILTER or DMX_SET_PES_FILTER.

int ioctl( int fd, int request = DMX_START);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_START for this command.

EBADF

fd is not a valid file descriptor.

EINVAL

Invalid argument, i.e. no filtering parameters provided via the DMX_SET_FILTER or DMX_SET_PES_FILTER functions.

EBUSY

This error code indicates that there are conflicting requests. There are active filters filtering data from another input source. Make sure that these filters are stopped before starting this filter.

This ioctl call is used to stop the actual filtering operation defined via the ioctl calls DMX_SET_FILTER or DMX_SET_PES_FILTER and started via the DMX_START command.

int ioctl( int fd, int request = DMX_STOP);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_STOP for this command.

EBADF

fd is not a valid file descriptor.

This ioctl call sets up a filter according to the filter and mask parameters provided. A timeout may be defined stating number of seconds to wait for a section to be loaded. A value of 0 means that no timeout should be applied. Finally there is a flag field where it is possible to state whether a section should be CRC-checked, whether the filter should be a ”one-shot” filter, i.e. if the filtering operation should be stopped after the first section is received, and whether the filtering operation should be started immediately (without waiting for a DMX_START ioctl call). If a filter was previously set-up, this filter will be canceled, and the receive buffer will be flushed.

int ioctl( int fd, int request = DMX_SET_FILTER, struct dmx_sct_filter_params ⋆params);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_SET_FILTER for this command.

struct dmx_sct_filter_params *params

Pointer to structure containing filter parameters.

EBADF

fd is not a valid file descriptor.

EINVAL

Invalid argument.

This ioctl call sets up a PES filter according to the parameters provided. By a PES filter is meant a filter that is based just on the packet identifier (PID), i.e. no PES header or payload filtering capability is supported.

The transport stream destination for the filtered output may be set. Also the PES type may be stated in order to be able to e.g. direct a video stream directly to the video decoder. Finally there is a flag field where it is possible to state whether the filtering operation should be started immediately (without waiting for a DMX_START ioctl call). If a filter was previously set-up, this filter will be cancelled, and the receive buffer will be flushed.

int ioctl( int fd, int request = DMX_SET_PES_FILTER, struct dmx_pes_filter_params ⋆params);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_SET_PES_FILTER for this command.

struct dmx_pes_filter_params *params

Pointer to structure containing filter parameters.

EBADF

fd is not a valid file descriptor.

EINVAL

Invalid argument.

EBUSY

This error code indicates that there are conflicting requests. There are active filters filtering data from another input source. Make sure that these filters are stopped before starting this filter.

This ioctl call is used to set the size of the circular buffer used for filtered data. The default size is two maximum sized sections, i.e. if this function is not called a buffer size of 2 * 4096 bytes will be used.

int ioctl( int fd, int request = DMX_SET_BUFFER_SIZE, unsigned long size);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_SET_BUFFER_SIZE for this command.

unsigned long size

Size of circular buffer.

EBADF

fd is not a valid file descriptor.

ENOMEM

The driver was not able to allocate a buffer of the requested size.

This ioctl call returns an event if available. If an event is not available, the behavior depends on whether the device is in blocking or non-blocking mode. In the latter case, the call fails immediately with errno set to EWOULDBLOCK. In the former case, the call blocks until an event becomes available.

The standard Linux poll() and/or select() system calls can be used with the device file descriptor to watch for new events. For select(), the file descriptor should be included in the exceptfds argument, and for poll(), POLLPRI should be specified as the wake-up condition. Only the latest event for each filter is saved.

int ioctl( int fd, int request = DMX_GET_EVENT, struct dmx_event ⋆ev);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_GET_EVENT for this command.

struct dmx_event *ev

Pointer to the location where the event is to be stored.

EBADF

fd is not a valid file descriptor.

EFAULT

ev points to an invalid address.

EWOULDBLOCK

There is no event pending, and the device is in non-blocking mode.

This ioctl call returns the current value of the system time counter (which is driven by a PES filter of type DMX_PES_PCR). Some hardware supports more than one STC, so you must specify which one by setting the num field of stc before the ioctl (range 0...n). The result is returned in form of a ratio with a 64 bit numerator and a 32 bit denominator, so the real 90kHz STC value is stc->stc / stc->base .

int ioctl( int fd, int request = DMX_GET_STC, struct dmx_stc ⋆stc);

int fd

File descriptor returned by a previous call to open().

int request

Equals DMX_GET_STC for this command.

struct dmx_stc *stc

Pointer to the location where the stc is to be stored.

EBADF

fd is not a valid file descriptor.

EFAULT

stc points to an invalid address.

EINVAL

Invalid stc number.