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It is believed that many inexperienced people have no idea about how to implement the function in Linux APM structure. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

It should be noted that Linux APM and acpi are conflicting modules, and users can only load one of them at the same time, and if they find that one of them is loaded when they are loading, they will exit automatically.

Function implementation in Linux APM structure

When a user process opens an apm_bios device, it calls this function

Static int apm_open (struct inode * inode, struct file * filp)

{

/ / this key is the Linux APM_user structure variable as, which is a bridge between the user and the Linux APM kernel. When a Linux APM event occurs, the event is hung on the queue of apm_user, so that when the user reads the event, it will read the relevant event and deal with it.

Struct apm_user * as

Lock_kernel ()

/ / assign a Linux APM_user structure to represent a user process

As = kzalloc (sizeof (* as), GFP_KERNEL)

/ / permissions settings such as read and write

If (as) {

As- > suser = capable (CAP_SYS_ADMIN)

As- > writer = (filp- > f_mode & FMODE_WRITE) = = FMODE_WRITE

As- > reader = (filp- > f_mode & FMODE_READ) = = FMODE_READ

/ / add this user to the user queue

Down_write & user_list_lock)

List_add (& as- > list, & apm_user_list)

Up_write & user_list_lock)

/ / this is a common way to pass private data

Filp- > private_data = as

}

Unlock_kernel ()

Return as? 0:-ENOMEM

}

This function is called when the user space process reads the device. The main function of this function is to read events into user space.

Static ssize_t apm_read (struct file * fp, char _ _ user * buf, size_t count, loff_t * ppos)

{

Struct apm_user * as = fp- > private_data

Apm_event_t event

Int I = count, ret = 0

If (count

Queue) & & fp- > f_flags & O_NONBLOCK)

Return-EAGAIN

/ / otherwise wait until the queue is not empty

Wait_event_interruptible (apm_waitqueue,! queue_empty (& as- > queue))

/ / copy the events in the queue to user space

While ((I > = sizeof (event)) & &! queue_empty (& as- > queue)) {

Event = queue_get_event (& as- > queue)

Ret =-EFAULT

If (copy_to_user (buf, & event, sizeof (event)

Break

After reading the above, have you mastered how to implement the functions in the Linux APM structure? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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