fe-open — Open a frontend device
|const char *device_name,|
Device to be opened.
Open flags. Access can either be
Multiple opens are allowed with
O_RDONLY. In this mode, only query and read ioctls are allowed.
Only one open is allowed in
O_RDWR. In this mode, all ioctls are allowed.
O_NONBLOCK flag is given, the system calls may return EAGAIN error code when no data is available or when the device driver is temporarily busy.
Other flags have no effect.
This system call opens a named frontend device (
for subsequent use. Usually the first thing to do after a successful open is to
find out the frontend type with FE_GET_INFO.
The device can be opened in read-only mode, which only allows monitoring of device status and statistics, or read/write mode, which allows any kind of use (e.g. performing tuning operations.)
In a system with multiple front-ends, it is usually the case that multiple devices cannot be open in read/write mode simultaneously. As long as a front-end device is opened in read/write mode, other open() calls in read/write mode will either fail or block, depending on whether non-blocking or blocking mode was specified. A front-end 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. This is a standard system call, documented in the Linux manual page for fcntl. When an open() call has succeeded, the device will be ready for use in the specified mode. This implies that the corresponding hardware is powered up, and that other front-ends may have been powered down to make that possible.
open returns the new file
descriptor. On error -1 is returned, and the
variable is set appropriately. Possible error codes are:
The caller has no permission to access the device.
The the device driver is already in use.
No device corresponding to this device special file exists.
Not enough kernel memory was available to complete the request.
The process already has the maximum number of files open.
The limit on the total number of files open on the system has been reached.
The device got removed.