linux-device-driver

In LDD3, i saw such codes static unsigned int scull_p_poll(struct file *filp, poll_table *wait) { struct scull_pipe *dev = filp->private_data; unsigned int mask = 0; /* * The buffer is circular; it is considered full * if "wp" is right behind "rp" and empty if the * two are equal. */ down(&dev->sem); poll_wait(filp, &dev->inq, wait); poll_wait(filp, &dev->outq, wait); if (dev->rp != dev->wp) mask |= POLLIN | POLLRDNORM; /* readable */ if (spacefree(dev)) mask |= POLLOUT | POLLWRNORM; /* writable */ up(&dev->sem); return mask; } But it says poll_wait won't wait and will return immediately. Then

This is related to this question . I'm not an expert on Linux device drivers or kernel modules, but I've been reading "Linux Device Drivers" [O'Reilly] by Rubini & Corbet and a number of online sources, but I haven't been able to find anything on this specific issue yet. When is a kernel or driver module allowed to use floating-point registers? If so, who is responsible for saving and restoring their contents? (Assume x86-64 architecture) If I understand correctly, whenever a KM is running, it is using a hardware context (or hardware thread or register set -- whatever you want to call it) that

I see u8 u16 u32 u64 data types being used in kernel code. And I am wondering why is there need to use u8 or u16 or u32 or u64 and not unsigned int ? Often when working close to the hardware or when trying to control the size/format of a data structure you need to have precise control of the size of your integers. As for u8 vs uint8_t , this is simply because Linux predated <stdint.h> being available in C, which is technically a C99-ism, but in my experience is available on most modern compilers even in their ANSI-C / C89 modes. Adding my 10 cents to this answer : u64 means an 'unsigned 64

I am on linux kernel 2.6.32. I am facing an issue in which one of the two ISR (serial and ethernet) are taking more time (hundreds of microseconds) on several occasion/under some scenarios which I don't know. I would like to get the time difference every time the ISR executes. What would be the best way (least expensive in terms of overhead involved). I don't see ARM architecture has some TSC register (read_tsc api) which would give me direct access to time as it offers on some other architecture. So Idea is 1) The moment ISR is invoked measure time 2) the moment ISR is complete measure the

I am trying to write a device driver and I need to use system() function in the driver. To use system() we need to include <stdlib.h> , which dosnt seem to work from a driver. It says no such file or directory found. Is there an alternative to stdlib.h for device drivers? Or an alternative to system() ? stdlib.h is a user space header. User space is that set of memory locations in which user processes (i.e., everything other than the kernel) run. A process is an executing instance of a program. One of the roles of the kernel is to manage individual user processes within this space and to

I was trying to read a loopback device that I have created through a kernel module in periods of 200ms, but it is crashing the kernel, when I try to insert it. I think there is problem with my read module, but it works fine without timer. I am new to kernel programming,please help. Thank you in advance:D #include <linux/kernel.h> #include <linux/module.h> #include <linux/timer.h> #include<linux/fs.h> #include <linux/init.h> #include <asm/segment.h> #include <asm/uaccess.h> #include <linux/buffer_head.h> static struct timer_list my_timer; static void read_file(char *filename) { struct file *fd;