Fix inittab back to adding /proc, fops sketch, scripts to automate debugfs

README.md

@@ -1,6 +1,6 @@
 # Linux Kernel Module Cheat
 
-Run one command, get into QEMU Buildroot BusyBox with several minimal Linux kernel module examples. Tested in Ubuntu 14.04.
+Run one command, get into QEMU Buildroot BusyBox with several minimal Linux kernel module example tutorials. Tested in Ubuntu 14.04.
 
 Usage:
 
@@ -30,3 +30,4 @@ The Linux kernel version can be found with:
         1. [hello](kernel_module/hello.c)
         1. [hello2](kernel_module/hello2.c)
         1. [debugfs](kernel_module/debugfs.c)
+        1. [fops](kernel_module/fops.c)

kernel_module/debugfs.c

@@ -1,17 +1,11 @@
 /*
 Adapted from: https://github.com/chadversary/debugfs-tutorial/blob/47b3cf7ca47208c61ccb51b27aac6f9f932bfe0b/example1/debugfs_example1.c
 
-Requires CONFIG_DEBUG_FS.
+Usage:
 
-	mkdir /debugfs
+	/debugfs.sh
-	mount -t debugfs none /debugfs
-	insmod /debugfs.ko
-	cd /debugfs/kernel_module_cheat
-	cat myfile
 
-Output:
+Requires `CONFIG_DEBUG_FS=y`.
-
-	42
 */
 
 #include <linux/debugfs.h>

kernel_module/fops.c

@@ -1,6 +1,10 @@
 /*
 dmesg stuff when fops happen.
 
+Usage:
+
+	/fops.sh
+
 fops define what the kernel will do on filesystem system calls on all of
 /dev, /proc, /sys, and consistute the main method of userland communication
 in drivers (syscalls being the other one).
@@ -19,19 +23,19 @@ static struct dentry *dir = 0;
 
 int fop_open(struct inode *inode, struct file *file)
 {
-	printk(KERN_INFO "open");
+	printk(KERN_INFO "open\n");
 	return 0;
 }
 
 ssize_t fop_read(struct file *file, char __user *buf, size_t len, loff_t *off)
 {
-	printk(KERN_INFO "read");
+	printk(KERN_INFO "read\n");
 	return 0;
 }
 
 ssize_t fop_write(struct file *file, const char __user *buf, size_t len, loff_t *off)
 {
-	printk(KERN_INFO "write");
+	printk(KERN_INFO "write\n");
 	return 0;
 }
 
@@ -41,7 +45,7 @@ http://stackoverflow.com/questions/11393674/why-is-the-close-function-is-called-
 */
 int fop_release (struct inode *inode, struct file *file)
 {
-	printk(KERN_INFO "release");
+	printk(KERN_INFO "release\n");
 	return 0;
 }
 

rootfs_overlay/debugfs.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+set -ex
+mkdir -p /debugfs
+mount -t debugfs none /debugfs
+insmod /debugfs.ko
+cd /debugfs/kernel_module_cheat
+cat myfile
+# => 42

rootfs_overlay/etc/inittab

@@ -1,3 +1,14 @@
 # /etc/inittab
+::sysinit:/bin/mount -t proc proc /proc
+::sysinit:/bin/mount -o remount,rw /
+::sysinit:/bin/mkdir -p /dev/pts
+::sysinit:/bin/mkdir -p /dev/shm
+::sysinit:/bin/mount -a
+::sysinit:/bin/hostname -F /etc/hostname
+::sysinit:/etc/init.d/rcS
 # https://unix.stackexchange.com/questions/299408/how-to-login-automatically-without-typing-root-in-buildroot-x86-64-qemu
 console::respawn:/bin/sh
+::ctrlaltdel:/sbin/reboot
+::shutdown:/etc/init.d/rcK
+::shutdown:/sbin/swapoff -a
+::shutdown:/bin/umount -a -r

rootfs_overlay/fops.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -ex
+insmod /fops.ko
+mkdir -p /fops
+mount -t debugfs none /fops
+cd /fops/kernel_module_cheat
+cat fops
+# => open
+# => read
+# => close
+# TODO.
+#echo a >fops