Code for: [Un]Register filesystem, [un]mount simplefs, Superblock placeholder

README

@@ -6,4 +6,39 @@ The source files are licensed under Creative Commons Zero License.
 More information at:	http://creativecommons.org/publicdomain/zero/1.0/
 Full license text at:	http://creativecommons.org/publicdomain/zero/1.0/legalcode
 
-To compile, install linux kernel sources and run make from the checkedout directory.
+To compile:
+------------
+install linux kernel sources and run make from the checkedout directory.
+
+To test:
+---------
+
+One-time-activity:
+
+linux-okb0:/home/psankar/src/simplefs > dd bs=1M count=100 if=/dev/zero of=image
+linux-okb0:/home/psankar/src/simplefs > mkdir mount
+
+Repeat everytime after making changes to the source:
+
+linux-okb0:/home/psankar/src/simplefs > make
+linux-okb0:/home/psankar/src/simplefs > su - ; # switch to root user if not already, or use sudo
+linux-okb0:/home/psankar/src/simplefs # dmesg
+linux-okb0:/home/psankar/src/simplefs # insmod simplefs.ko
+linux-okb0:/home/psankar/src/simplefs # dmesg
+[ 7467.426112] Sucessfully registered simplefs
+linux-okb0:/home/psankar/src/simplefs # mount -o loop -t simplefs image /home/psankar/src/simplefs/mount/
+linux-okb0:/home/psankar/src/simplefs # dmesg
+[ 7467.426112] Sucessfully registered simplefs
+[ 7478.223432] simplefs is succesfully mounted on [/dev/loop1]
+linux-okb0:/home/psankar/src/simplefs # umount /home/psankar/src/simplefs/mount/
+linux-okb0:/home/psankar/src/simplefs # dmesg
+[ 7467.426112] Sucessfully registered simplefs
+[ 7478.223432] simplefs is succesfully mounted on [/dev/loop1]
+[ 7498.889439] simplefs superblock is destroyed. Unmount succesful.
+linux-okb0:/home/psankar/src/simplefs # rmmod simplefs.ko
+linux-okb0:/home/psankar/src/simplefs # dmesg
+[ 7467.426112] Sucessfully registered simplefs
+[ 7478.223432] simplefs is succesfully mounted on [/dev/loop1]
+[ 7498.889439] simplefs superblock is destroyed. Unmount succesful.
+[ 7506.906067] Sucessfully unregistered simplefs
+linux-okb0:/home/psankar/src/simplefs #

simple.c

@@ -7,16 +7,117 @@
 
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/fs.h>
+
+/* This function creates, configures and returns an inode,
+ * for the asked file (or) directory (differentiated by the mode param),
+ * under the directory specified by the dir param
+ * on the device dev, managed by the superblock sb param) */
+struct inode *simplefs_get_inode(struct super_block *sb,
+				 const struct inode *dir, umode_t mode,
+				 dev_t dev)
+{
+	struct inode *inode = new_inode(sb);
+
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		inode_init_owner(inode, dir, mode);
+
+		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+
+		switch (mode & S_IFMT) {
+		case S_IFDIR:
+			/* i_nlink will be initialized to 1 in the inode_init_always function
+			 * (that gets called inside the new_inode function),
+			 * We change it to 2 for directories, for covering the "." entry */
+			inc_nlink(inode);
+			break;
+		case S_IFREG:
+		case S_IFLNK:
+		default:
+			printk(KERN_ERR
+			       "simplefs can create meaningful inode for only root directory at the moment\n");
+			return NULL;
+			break;
+		}
+	}
+	return inode;
+}
+
+/* This function, as the name implies, Makes the super_block valid and
+ * fills filesystem specific information in the super block */
+int simplefs_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct inode *inode;
+
+	/* A magic number that uniquely identifies our filesystem type */
+	sb->s_magic = 0x10032013;
+
+	inode = simplefs_get_inode(sb, NULL, S_IFDIR, 0);
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static struct dentry *simplefs_mount(struct file_system_type *fs_type,
+				     int flags, const char *dev_name,
+				     void *data)
+{
+	struct dentry *ret;
+
+	ret = mount_bdev(fs_type, flags, dev_name, data, simplefs_fill_super);
+
+	if (unlikely(IS_ERR(ret)))
+		printk(KERN_ERR "Error mounting simplefs");
+	else
+		printk(KERN_INFO "simplefs is succesfully mounted on [%s]\n",
+		       dev_name);
+
+	return ret;
+}
+
+static void simplefs_kill_superblock(struct super_block *s)
+{
+	printk(KERN_INFO
+	       "simplefs superblock is destroyed. Unmount succesful.\n");
+	/* This is just a dummy function as of now. As our filesystem gets matured,
+	 * we will do more meaningful operations here */
+	return;
+}
+
+struct file_system_type simplefs_fs_type = {
+	.owner = THIS_MODULE,
+	.name = "simplefs",
+	.mount = simplefs_mount,
+	.kill_sb = simplefs_kill_superblock,
+};
 
 static int simplefs_init(void)
 {
-        printk(KERN_ALERT "Hello World\n");
+	int ret;
-        return 0;
+
+	ret = register_filesystem(&simplefs_fs_type);
+	if (likely(ret == 0))
+		printk(KERN_INFO "Sucessfully registered simplefs\n");
+	else
+		printk(KERN_ERR "Failed to register simplefs. Error:[%d]", ret);
+
+	return ret;
 }
 
 static void simplefs_exit(void)
 {
-        printk(KERN_ALERT "Goodbye World\n");
+	int ret;
+
+	ret = unregister_filesystem(&simplefs_fs_type);
+
+	if (likely(ret == 0))
+		printk(KERN_INFO "Sucessfully unregistered simplefs\n");
+	else
+		printk(KERN_ERR "Failed to unregister simplefs. Error:[%d]",
+		       ret);
 }
 
 module_init(simplefs_init);