Not able to read all data from buffer in kernel read function

Question

Here is my code for read function in proc kernel module

int read_proc(struct file *filp,char *buf,size_t count,loff_t *offset ) 
{
    struct task_struct *task = current;         
    ssize_t bytes = count < (MAX_MSG_LEN-(*offset)) ? count : (MAX_MSG_LEN-(*offset));

    do
    {
        task = task->parent;
        sprintf(buf, "assignment: parent process: %s, PID: %d Utime: %d , stime: %ld \n ", task->comm, task->pid,task->utime,task->stime) ;  
    } while (task->pid != 0);

    (*offset) += bytes;
    return bytes;
}

In this code I'm only able to read the last zero number PID process from the buffer but I want to read all the running processes and its PID

I have modified the code from this link: https://jlmedina123.wordpress.com/2013/08/13/current-variable-and-task_struct/

My output:

assignment: parent process: swapper/0, PID: 0 Utime: 0 , stime: 1201744387 

668726 
assignment: parent process: swapper/0, PID: 0 Utime: 0 , stime: 1201761343 

195869 
assignment: parent process: swapper/0, PID: 0 Utime: 0 , stime: 1201791953

I want to read all the process id and running process which i have copied into the buffer !!! please tell me where I have done wrong?

Is it a *Linux* kernel module? Please edit your question to include proper tags. — Some programmer dude, Jul 12 '17 at 10:04
To read the buffer from my module I use "cat /proc/module_name" command. — Bhagyesh Mulage, Jul 12 '17 at 10:06
``do { ... } while (...)`` is sometimes frowned upon. The code is executed at least once and what if the magical (global variable?) ``current`` has no parent in the first place? — BitTickler, Jul 12 '17 at 10:10
Actually `current` I have used to read the current running process. But I have not used yet in my code. — Bhagyesh Mulage, Jul 12 '17 at 10:14
Seems to me that you keep overwriting `buf` in the loop, i.e. `buf` will only contain data from the last loop (which has pid equal zero) — Support Ukraine, Jul 12 '17 at 10:41
Perhaps this can help https://stackoverflow.com/questions/2674312/how-to-append-strings-using-sprintf — Support Ukraine, Jul 12 '17 at 11:00
Thank you !!!!! so much ......my problem is get resolved ...The problem is with the buffer overwriting .....and it gets resolved by `strlen(buf)` function — Bhagyesh Mulage, Jul 12 '17 at 11:16
It's easier if you use `single_open` and the `seq_file` interface. See "fs/proc/version.c" in the Linux kernel sources for a very simple example. — Ian Abbott, Jul 12 '17 at 16:14

Not able to read all data from buffer in kernel read function

0 Answers0