mkfs-simplefs: An utility to create simplefs on a device.

Makefile

@@ -1,8 +1,14 @@
 obj-m := simplefs.o
 simplefs-objs := simple.o
 
-all:
+all: ko mkfs-simplefs
+
+ko:
 	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
 
+mkfs-simplefs_SOURCES:
+	mkfs-simplefs.c simple.h
+
 clean:
 	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+	rm mkfs-simplefs

README

@@ -15,7 +15,7 @@ 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 > dd bs=4096 count=100 if=/dev/zero of=image
 linux-okb0:/home/psankar/src/simplefs > mkdir mount
 
 Repeat everytime after making changes to the source:
@@ -23,17 +23,14 @@ 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 -c
-linux-okb0:/home/psankar/src/simplefs # insmod simplefs.ko ; mount -o loop -t simplefs image /home/psankar/src/simplefs/mount/ ; dmesg
-[ 5788.269663] Sucessfully registered simplefs
-[ 5788.274803] simplefs is succesfully mounted on [/dev/loop2]
-linux-okb0:/home/psankar/src/simplefs # cd mount/
-linux-okb0:/home/psankar/src/simplefs/mount # ls
-linux-okb0:/home/psankar/src/simplefs/mount # cd ..
-linux-okb0:/home/psankar/src/simplefs # umount mount ; rmmod simplefs.ko
-linux-okb0:/home/psankar/src/simplefs # dmesg
-[ 5788.269663] Sucessfully registered simplefs
-[ 5788.274803] simplefs is succesfully mounted on [/dev/loop2]
-[ 5814.008604] simplefs superblock is destroyed. Unmount succesful.
-[ 5814.014065] Sucessfully unregistered simplefs
+# Creating a loop back device and formatting it with our shiny, brand new simplefs
+
+linux-okb0:/home/psankar/src/simplefs # losetup /dev/loop0
+losetup: /dev/loop0: No such file or directory
+linux-okb0:/home/psankar/src/simplefs # losetup /dev/loop0 image
+linux-okb0:/home/psankar/src/simplefs # ./mkfs-simplefs /dev/loop0
+Super block written succesfully
+linux-okb0:/home/psankar/src/simplefs # losetup -d /dev/loop0
+linux-okb0:/home/psankar/src/simplefs # losetup /dev/loop0
+losetup: /dev/loop0: No such file or directory
 linux-okb0:/home/psankar/src/simplefs #

mkfs-simplefs.c

@@ -0,0 +1,44 @@
+#include "simple.h"
+
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+int main(int argc, char *argv[])
+{
+	int fd;
+	ssize_t ret;
+	struct simplefs_super_block sb;
+
+	if (argc != 2) {
+		printf("Usage: mkfs-simplefs <device>\n");
+		return -1;
+	}
+
+	fd = open(argv[1], O_RDWR);
+	if (fd == -1) {
+		perror("Error opening the device");
+		return -1;
+	}
+
+	sb.version = 1;
+	sb.magic = SIMPLEFS_MAGIC;
+	sb.block_size = SIMPLEFS_DEFAULT_BLOCK_SIZE;
+	sb.free_blocks = ~0;
+
+	ret = write(fd, (char *)&sb, sizeof(sb));
+
+	/* Just a redundant check. Not required ideally. */
+	if (ret != SIMPLEFS_DEFAULT_BLOCK_SIZE)
+		printf
+		    ("bytes written [%d] are not equal to the default block size",
+		     (int)ret);
+	else
+		printf("Super block written succesfully");
+
+	close(fd);
+
+	return 0;
+}

simple.c

@@ -9,6 +9,8 @@
 #include <linux/module.h>
 #include <linux/fs.h>
 
+#include "simple.h"
+
 static int simplefs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
 	/* ls will list nothing as of now.
@@ -76,7 +78,7 @@ 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;
+	sb->s_magic = SIMPLEFS_MAGIC;
 
 	inode = simplefs_get_inode(sb, NULL, S_IFDIR, 0);
 	inode->i_op = &simplefs_inode_ops;

simple.h

@@ -0,0 +1,11 @@
+const int SIMPLEFS_MAGIC = 0x10032013;
+const int SIMPLEFS_DEFAULT_BLOCK_SIZE = 4 * 1024;
+
+struct simplefs_super_block {
+	unsigned int version;
+	unsigned int magic;
+	unsigned int block_size;
+	unsigned int free_blocks;
+
+	char padding[ (4 * 1024) - (4 * sizeof(unsigned int))];
+};