DamnOS + DamnFS

DamnOS is an operating system based on MIT 6.828 JOS , and DamnFS is just a self-designed brained-fucked simple ext-like File System that DamnOS relies on.

This is a simple combination of DamnOS and DamnFS like:

DamnOS in hda:
| 512b  |       2m      |
-------------------------
| boot  |    kernel     |
| sect  |   (DamnOs)    |
-------------------------

DanmFs in hdb:
|            16m + 8K           |
---------------------------------
|  4K       4K         16M      |
| Super |  inodes |    ...      |
---------------------------------

The structure of DamnFs can be viewed at the back of this doc.

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To Boot

Dependencies : Qemu

-make qemu

This instruction automatically allocate 8M to the simple ugly kernel.

There are two page directory were used in total when booting. The first one is pre-defined in entrypgdir.c and deprecated after the REAL page directory set up and properly mapped in function mem_init().

For more detail, go check out init.c and pmap.c.

Other information is written in my report.

Ctrl-a + x to exit.

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Intro to DamnFS

DamnFS is a simple ext-like file system. It has 128 inodes and 4096 blocks. (Of course it's not practical) Although it's small and simple, with ./damn you can still apply ls, touch, mkdir, rm, cat and edit on it, just like in linux. The reason it's not fat-like is that I think a file system should be slim.

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Details

• The structure of the super block. block_avai records the availability of each block, similar to inode_avai.

struct DamnSuper{
	uint32_t magic;
	uint16_t in_num;
	uint16_t blk_num;
	uint16_t in_size;
	uint16_t blk_size;
	uintptr_t in_entry;
	uint32_t blk_ocp[MAXBLKNUM/32];
	uint32_t in_ocp[MAXINODENUM/32];
} __attribute__((aligned(BLKSIZE)));

• The structure of inode. Obviously, an inode can records 8 block indices. The file system doesn't support indirect search for blocks.

struct DamnInode{
	uint16_t type;
	uint16_t size;
	uint16_t blk_used;
	uint16_t blk_ind[NDIRECT];
} __attribute__((packed));

• The struture of directory entry:

struct DirEntry{
	char f_name[MAXNAMELEN];
	uint16_t in_ind;
} __attribute__((packed));;
};

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Usage:

-make fs.img

Then you can get a proper formatted "fs.img" in current dir.

Now the file system it's yours. You can use ./damn [command] [path] to modify the file system. The supported commands are listed in the introduction part.

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Tips

• You can only remove a directory when there are only "." and ".." in it.