I'm using Kubuntu Gutsy (7.10) and trying to learn something about kernel programming with the tldp.org tutorial.
Works fine, but here I get an error message by compiling the procfs3.c sample:

"/home/tobias/kernel/procfs3.c:114: error: dereferencing pointer to incomplete type"

Can anyone explain what's the problem and how to correct it?

gcc (GCC) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
Re: error message by compiling procfs3.c
April 04, 2008 06:33AM

took me some time to figure this out, but "current" as it is used in this example in the function module_permission (I'm working through this tutorial myself too, currently) has to be defined, which happens in <linux/sched.h>. So a way to solve this problem, is including this header file at the beginning of procfs3.c

The beginning of this file would then look like:
 *  procfs3.c -  create a "file" in /proc, use the file_operation way
 *              to manage the file.
#include <linux/kernel.h>       /* We're doing kernel work */
#include <linux/module.h>       /* Specifically, a module */
#include <linux/proc_fs.h>      /* Necessary because we use proc fs */
#include <asm/uaccess.h>        /* for copy_*_user */
#include <linux/sched.h>	/* for task properties (euid) */

#define PROC_ENTRY_FILENAME     "buffer2k"
#define PROCFS_MAX_SIZE         2048
(Note the additional include for sched.h)

Hope this helps,
After adding the sched.h line, the error now is:
procfs3.c:115: error: ‘struct task_struct’ has no member named ‘euid’

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