How to fix error: passing argument 4 of 'proc_create' from incompatible pointer type

Question

I am trying to load things to my kernel to learn about how you can add things!

I have two files here!

Below is skynet.c:

#include <linux/module.h>    // included for all kernel modules
#include <linux/kernel.h>    // included for KERN_INFO
#include <linux/init.h>      // included for __init and __exit macros

#include <linux/proc_fs.h>   // file operations
#include <linux/seq_file.h>  // seq_read, ...

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Dr. Dyson");
MODULE_DESCRIPTION("Global Information Grid");

static int skynet_show(struct seq_file *m, void *v);

static int skynet_open(struct inode *inode, struct  file *file);

static const struct file_operations skynet_fops = {
  .owner = THIS_MODULE,
  .open = skynet_open,
  .read = seq_read,
  .llseek = seq_lseek,
  .release = single_release,
};


static int skynet_show(struct seq_file *m, void *v) {
 here:
  seq_printf(m, "Skynet location: 0x%lx\n", (unsigned long)&&here);
  return 0;
}

static int skynet_open(struct inode *inode, struct  file *file) {
  return single_open(file, skynet_show, NULL);
}


static int __init skynet_init(void) {
  proc_create("skynet", 0, NULL, &skynet_fops);
  printk(KERN_INFO "Skynet in control\n");

  return 0;
}

static void __exit skynet_cleanup(void) {
  remove_proc_entry("skynet", NULL);
  printk(KERN_INFO "I'll be back!\n");
}

module_init(skynet_init);
module_exit(skynet_cleanup);

Below here is the Makefile:

obj-m += skynet.o

all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

But when i write in make i get this error in the terminal below:

make -C /lib/modules/5.8.0-29-generic/build M=/home/jonteyh/ID1200/Device/skynet modules
make[1]: Entering directory '/usr/src/linux-headers-5.8.0-29-generic'
  CC [M]  /home/jonteyh/ID1200/Device/skynet/skynet.o
/home/jonteyh/ID1200/Device/skynet/skynet.c: In function ‘skynet_init’:
/home/jonteyh/ID1200/Device/skynet/skynet.c:37:34: error: passing argument 4 of ‘proc_create’ from incompatible pointer type [-Werror=incompatible-pointer-types]
   37 |   proc_create("skynet", 0, NULL, &skynet_fops);
      |                                  ^~~~~~~~~~~~
      |                                  |
      |                                  const struct file_operations *
In file included from /home/jonteyh/ID1200/Device/skynet/skynet.c:5:
./include/linux/proc_fs.h:107:122: note: expected ‘const struct proc_ops *’ but argument is of type ‘const struct file_operations *’
  107 | struct proc_dir_entry *proc_create(const char *name, umode_t mode, struct proc_dir_entry *parent, const struct proc_ops *proc_ops);
      |                                                                                                   ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:290: /home/jonteyh/ID1200/Device/skynet/skynet.o] Error 1
make[1]: *** [Makefile:1780: /home/jonteyh/ID1200/Device/skynet] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-5.8.0-29-generic'
make: *** [Makefile:4: all] Error 2

What i have tried is to change is file_operations to proc_ops the things below:

static const struct proc_ops skynet_fops = {
  .owner = THIS_MODULE,
  .open = skynet_open,
  .read = seq_read,
  .llseek = seq_lseek,
  .release = single_release,
};

But then i got other errors such like release dosen't exist. How can i solve this error incompatible??

Answer 1

There are two solutions.

The first solution is to replace struct file_operations with struct proc_ops for kernel version 5.6 or later:

#include <linux/version.h>
#include <linux/module.h>    // included for all kernel modules
#include <linux/kernel.h>    // included for KERN_INFO
#include <linux/init.h>      // included for __init and __exit macros

#include <linux/proc_fs.h>   // file operations
#include <linux/seq_file.h>  // seq_read, ...

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Dr. Dyson");
MODULE_DESCRIPTION("Global Information Grid");

#if LINUX_VERSION_CODE >= KERNEL_VERSION(5,6,0)
#define HAVE_PROC_OPS
#endif

static int skynet_show(struct seq_file *m, void *v);

static int skynet_open(struct inode *inode, struct  file *file);

#ifdef HAVE_PROC_OPS
static const struct proc_ops skynet_ops = {
  .proc_open = skynet_open,
  .proc_read = seq_read,
  .proc_lseek = seq_lseek,
  .proc_release = single_release,
};
#else
static const struct file_operations skynet_ops = {
  .owner = THIS_MODULE,
  .open = skynet_open,
  .read = seq_read,
  .llseek = seq_lseek,
  .release = single_release,
};
#endif


static int skynet_show(struct seq_file *m, void *v) {
 here:
  seq_printf(m, "Skynet location: 0x%lx\n", (unsigned long)&&here);
  return 0;
}

static int skynet_open(struct inode *inode, struct  file *file) {
  return single_open(file, skynet_show, NULL);
}


static int __init skynet_init(void) {
  proc_create("skynet", 0, NULL, &skynet_ops);
  printk(KERN_INFO "Skynet in control\n");

  return 0;
}

static void __exit skynet_cleanup(void) {
  remove_proc_entry("skynet", NULL);
  printk(KERN_INFO "I'll be back!\n");
}

module_init(skynet_init);
module_exit(skynet_cleanup);

The second solution is to replace proc_create with proc_create_single for kernel version 4.18 or later when all that is required is a basic, read-only proc file:

#include <linux/version.h>
#include <linux/module.h>    // included for all kernel modules
#include <linux/kernel.h>    // included for KERN_INFO
#include <linux/init.h>      // included for __init and __exit macros

#include <linux/proc_fs.h>   // file operations
#include <linux/seq_file.h>  // seq_read, ...

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Dr. Dyson");
MODULE_DESCRIPTION("Global Information Grid");

#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,18,0)
#define HAVE_PROC_CREATE_SINGLE
#endif


static int skynet_show(struct seq_file *m, void *v) {
 here:
  seq_printf(m, "Skynet location: 0x%lx\n", (unsigned long)&&here);
  return 0;
}

#ifndef HAVE_PROC_CREATE_SINGLE
static int skynet_open(struct inode *inode, struct  file *file) {
  return single_open(file, skynet_show, NULL);
}

static const struct file_operations skynet_fops = {
  .owner = THIS_MODULE,
  .open = skynet_open,
  .read = seq_read,
  .llseek = seq_lseek,
  .release = single_release,
};
#endif


static int __init skynet_init(void) {
#ifdef HAVE_PROC_CREATE_SINGLE
  proc_create_single("skynet", 0, NULL, skynet_show);
#else
  proc_create("skynet", 0, NULL, &skynet_fops);
#endif
  printk(KERN_INFO "Skynet in control\n");

  return 0;
}

static void __exit skynet_cleanup(void) {
  remove_proc_entry("skynet", NULL);
  printk(KERN_INFO "I'll be back!\n");
}

module_init(skynet_init);
module_exit(skynet_cleanup);