@brief Reserve a single line.
@param line GPIO line object.
@param config Request options.
@param default_val Initial line value - only relevant if we're setting
the direction to output.
@return 0 if the line was properly reserved. In case of an error this
routine returns -1 and sets the last error number.
If this routine succeeds, the caller takes ownership of the GPIO line until
it's released.
@brief Reserve a single line. @param line GPIO line object. @param config Request options. @param default_val Initial line value - only relevant if we're setting the direction to output. @return 0 if the line was properly reserved. In case of an error this routine returns -1 and sets the last error number.
If this routine succeeds, the caller takes ownership of the GPIO line until it's released.