Android Training Course (19)

In the init initialization process, how does one initialize the device? To understand this, you need to carefully analyze the following code:

#001 int device_init (void)

#002 {

#003 suseconds_t t0, t1;

#004 int fd;

#005

#006 fd = open_uevent_socket ();

#007 if (fd <0)

#008 return-1;

This Code calls the open_uevent_socket function to create a socket for the user's event space.

 

#009

#010 fcntl (fd, F_SETFD, FD_CLOEXEC );

#011 fcntl (fd, F_SETFL, O_NONBLOCK );

This Code sets the socket attribute. FD_CLOEXEC is used to set the close-on-exec Status standard of the file. When the close-on-exec flag is 0 after exec () is called, this file is not closed. If it is not zero, it is disabled after exec. The default close-on-exec Status is 0 and needs to be set through FD_CLOEXEC. O_NONBLOCK sets this socket as an asynchronous communication method.

 

#012

#013 t0 = get_usecs ();

This line of code is used to obtain the time of the current user.

 

#014 coldboot (fd, "/sys/class ");

#015 coldboot (fd, "/sys/block ");

#016 coldboot (fd, "/sys/devices ");

This code is used to traverse all the devices that have been created before the init process and find the device Event file to send event notifications.

 

#017 t1 = get_usecs ();

This line of code is used to obtain the time of the current user.

 

#018

#019 log_event_print ("coldboot % ld uS", (long) (t1-t0 )));

This line of code is used to print the number of seconds of the output cold start.

 

#020

#021 return fd;

#022}

#023