procfs example, S99 symlink

README.md

@@ -213,6 +213,8 @@ and they will be run automatically before the login prompt.
 
 `S99` is already gitignored for you.
 
+For convenience, we also setup a symlink from `S99` to `rootfs_overlay/etc/init.d/S99`.
+
 ## Debugging
 
 To GDB the Linux kernel, first run:

S99

@@ -0,0 +1 @@
+rootfs_overlay/etc/init.d/S99

kernel_module/README.md

@@ -5,9 +5,11 @@
     1.  Debugging
         1.  [hello](hello.c)
         1.  [hello2](hello2.c)
-        1.  [debugfs](debugfs.c)
         1.  [panic](panic.c)
     1.  [params](params.c)
+    1.  Pseudo filesystems
+        1.  [debugfs](debugfs.c)
+        1.  [procfs](procfs.c)
     1.  [fops](fops.c)
         1.  [ioctl](ioctl.c)
         1.  [poll](poll.c)

kernel_module/procfs.c

@@ -0,0 +1,54 @@
+/*
+Yet another fops entrypoint.
+
+https://stackoverflow.com/questions/8516021/proc-create-example-for-kernel-module
+
+	insmod /procfs.ko
+	cat /proc/lkmc_procfs
+
+Output:
+
+	abcd
+*/
+
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h> /* seq_read, seq_lseek, single_open, single_release */
+#include <uapi/linux/stat.h> /* S_IRUSR */
+
+static const char *filename = "lkmc_procfs";
+
+static int show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "abcd\n");
+	return 0;
+}
+
+static int open(struct inode *inode, struct  file *file)
+{
+	return single_open(file, show, NULL);
+}
+
+static const struct file_operations fops = {
+	.llseek = seq_lseek,
+	.open = open,
+	.owner = THIS_MODULE,
+	.read = seq_read,
+	.release = single_release,
+};
+
+static int myinit(void)
+{
+	proc_create(filename, 0, NULL, &fops);
+	return 0;
+}
+
+static void myexit(void)
+{
+	remove_proc_entry(filename, NULL);
+}
+
+module_init(myinit)
+module_exit(myexit)
+MODULE_LICENSE("GPL");