7.69. V4L2 open()¶
7.69.1. Name¶
v4l2-open - Open a V4L2 device
7.69.2. Synopsis¶
#include <fcntl.h>
- 
int open(const char *device_name, int flags)¶
7.69.3. Arguments¶
- device_name
- Device to be opened. 
- flags
- Open flags. Access mode must be - O_RDWR. This is just a technicality, input devices still support only reading and output devices only writing.- When the - O_NONBLOCKflag is given, the- read()function and the VIDIOC_DQBUF ioctl will return the- EAGAINerror code when no data is available or no buffer is in the driver outgoing queue, otherwise these functions block until data becomes available. All V4L2 drivers exchanging data with applications must support the- O_NONBLOCKflag.- Other flags have no effect. 
7.69.4. Description¶
To open a V4L2 device applications call open() with the
desired device name. This function has no side effects; all data format
parameters, current input or output, control values or other properties
remain unchanged. At the first open() call after loading the
driver they will be reset to default values, drivers are never in an
undefined state.
7.69.5. Return Value¶
On success open() returns the new file descriptor. On error
-1 is returned, and the errno variable is set appropriately.
Possible error codes are:
- EACCES
- The caller has no permission to access the device. 
- EBUSY
- The driver does not support multiple opens and the device is already in use. 
- ENODEV
- Device not found or was removed. 
- ENOMEM
- Not enough kernel memory was available to complete the request. 
- EMFILE
- The process already has the maximum number of files open. 
- ENFILE
- The limit on the total number of files open on the system has been reached.