diff --git a/Makefile b/Makefile
index fa7b33b..34b0be2 100644
--- a/Makefile
+++ b/Makefile
@@ -69,6 +69,12 @@ xv6.img: bootblock kernel
 	dd if=bootblock of=xv6.img conv=notrunc
 	dd if=kernel of=xv6.img seek=1 conv=notrunc
 
+mkfs: src/mkfs.rs
+	rustc -W warnings -o mkfs src/mkfs.rs
+
+fs.img: mkfs *.txt
+	./mkfs fs.img *.txt
+
 bootblock: bootasm.S bootmain.c
 	$(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c bootmain.c
 	$(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c bootasm.S
@@ -88,6 +94,7 @@ kernel: kernel.a $(OBJS) ./linkers/kernel.ld
 vectors.S: vectors.pl
 	./vectors.pl > vectors.S
 
+
 # $(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o kernel.a -b binary
 # ld -m    elf_i386 -T kernel.ld -o kernel entry.o kernel.a -b binary
 # Prevent deletion of intermediate files, e.g. cat.o, after first build, so
@@ -100,7 +107,7 @@ vectors.S: vectors.pl
 
 clean: 
 	rm -f *.tex *.dvi *.idx *.aux *.log *.ind *.ilg \
-	*.a *.o *.d *.asm *.sym bootblock kernel xv6.img .gdbinit vectors.S
+	*.a *.o *.d *.asm *.sym bootblock kernel xv6.img fs.img mkfs .gdbinit vectors.S
 	rm -r target
 
 # run in emulators
diff --git a/src/mkfs.rs b/src/mkfs.rs
new file mode 100644
index 0000000..9bfb77b
--- /dev/null
+++ b/src/mkfs.rs
@@ -0,0 +1,359 @@
+use std::env;
+use std::fs::{File, OpenOptions};
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::mem::size_of;
+use std::path::Path;
+
+
+// constants to be included in constants.rs under "FILE SYSTEM" section,
+// declared here for now to avoid merge conflicts
+
+const BSIZE: usize = 512;
+const FSSIZE: u32 = 10_000;
+const NINODES: u32 = 200;
+const LOGSIZE: u32 = 30;
+
+const ROOTINO: u32 = 1;
+const NDIRECT: usize = 12;
+const NINDIRECT: usize = BSIZE / size_of::<u32>();
+const MAXFILE: usize = NDIRECT + NINDIRECT;
+const DIRSIZ: usize = 14;
+
+const T_DIR: u16 = 1;
+const T_FILE: u16 = 2;
+
+#[repr(C)]
+#[derive(Clone, Copy, Default)]
+struct Superblock {
+	size: u32,
+	nblocks: u32,
+	ninodes: u32,
+	nlog: u32,
+	logstart: u32,
+	inodestart: u32,
+	bmapstart: u32,
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+struct Dinode {
+	typ: u16,
+	major: u16,
+	minor: u16,
+	nlink: u16,
+	size: u32,
+	addrs: [u32; NDIRECT + 1],
+}
+
+impl Default for Dinode {
+	fn default() -> Self {
+		Self {
+			typ: 0,
+			major: 0,
+			minor: 0,
+			nlink: 0,
+			size: 0,
+			addrs: [0; NDIRECT + 1],
+		}
+	}
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+struct Dirent {
+	inum: u16,
+	name: [u8; DIRSIZ],
+}
+
+impl Default for Dirent {
+	fn default() -> Self {
+		Self {
+			inum: 0,
+			name: [0; DIRSIZ],
+		}
+	}
+}
+
+struct Mkfs {
+	fsfd: File,
+	sb: Superblock,
+	freeinode: u32,
+	freeblock: u32,
+}
+
+fn as_bytes<T>(val: &T) -> &[u8] {
+	unsafe { std::slice::from_raw_parts((val as *const T).cast::<u8>(), size_of::<T>()) }
+}
+
+fn from_bytes<T: Copy>(bytes: &[u8]) -> T {
+	assert_eq!(bytes.len(), size_of::<T>());
+	let mut out = std::mem::MaybeUninit::<T>::uninit();
+	unsafe {
+		std::ptr::copy_nonoverlapping(bytes.as_ptr(), out.as_mut_ptr().cast::<u8>(), bytes.len());
+		out.assume_init()
+	}
+}
+
+fn name_to_dirent(name: &str, inum: u16) -> Dirent {
+	let mut de = Dirent {
+		inum: inum.to_le(),
+		..Default::default()
+	};
+	let name_bytes = name.as_bytes();
+	let copy_len = name_bytes.len().min(DIRSIZ);
+	de.name[..copy_len].copy_from_slice(&name_bytes[..copy_len]);
+	de
+}
+
+impl Mkfs {
+	fn new(fsfd: File, sb: Superblock, freeblock: u32) -> Self {
+		Self {
+			fsfd,
+			sb,
+			freeinode: 1,
+			freeblock,
+		}
+	}
+
+	fn wsect(&mut self, sec: u32, buf: &[u8; BSIZE]) {
+		let off = (sec as u64) * (BSIZE as u64);
+		self.fsfd
+			.seek(SeekFrom::Start(off))
+			.expect("lseek(write) failed");
+		self.fsfd.write_all(buf).expect("write failed");
+	}
+
+	fn rsect(&mut self, sec: u32, buf: &mut [u8; BSIZE]) {
+		let off = (sec as u64) * (BSIZE as u64);
+		self.fsfd
+			.seek(SeekFrom::Start(off))
+			.expect("lseek(read) failed");
+		self.fsfd.read_exact(buf).expect("read failed");
+	}
+
+	fn iblock(&self, inum: u32) -> u32 {
+		(inum / ipb() as u32) + u32::from_le(self.sb.inodestart)
+	}
+
+	fn winode(&mut self, inum: u32, ip: &Dinode) {
+		let mut buf = [0u8; BSIZE];
+		let bn = self.iblock(inum);
+		self.rsect(bn, &mut buf);
+
+		let off = (inum as usize % ipb()) * size_of::<Dinode>();
+		let src = as_bytes(ip);
+		buf[off..off + size_of::<Dinode>()].copy_from_slice(src);
+		self.wsect(bn, &buf);
+	}
+
+	fn rinode(&mut self, inum: u32) -> Dinode {
+		let mut buf = [0u8; BSIZE];
+		let bn = self.iblock(inum);
+		self.rsect(bn, &mut buf);
+
+		let off = (inum as usize % ipb()) * size_of::<Dinode>();
+		from_bytes::<Dinode>(&buf[off..off + size_of::<Dinode>()])
+	}
+
+	fn ialloc(&mut self, typ: u16) -> u32 {
+		let inum = self.freeinode;
+		self.freeinode += 1;
+
+		let din = Dinode {
+			typ: typ.to_le(),
+			nlink: 1u16.to_le(),
+			size: 0u32.to_le(),
+			..Default::default()
+		};
+		self.winode(inum, &din);
+		inum
+	}
+
+	fn balloc(&mut self, used: u32) {
+		assert!(used < (BSIZE * 8) as u32);
+		println!("balloc: first {} blocks have been allocated", used);
+
+		let mut buf = [0u8; BSIZE];
+		for i in 0..used {
+			let idx = (i / 8) as usize;
+			let bit = (i % 8) as u8;
+			buf[idx] |= 1u8 << bit;
+		}
+
+		let bmapstart = u32::from_le(self.sb.bmapstart);
+		println!("balloc: write bitmap block at sector {}", bmapstart);
+		self.wsect(bmapstart, &buf);
+	}
+
+	fn iappend(&mut self, inum: u32, mut p: &[u8]) {
+		let mut din = self.rinode(inum);
+		let mut off = u32::from_le(din.size);
+
+		while !p.is_empty() {
+			let fbn = (off as usize) / BSIZE;
+			assert!(fbn < MAXFILE);
+
+			let x: u32;
+			if fbn < NDIRECT {
+				if u32::from_le(din.addrs[fbn]) == 0 {
+					din.addrs[fbn] = self.freeblock.to_le();
+					self.freeblock += 1;
+				}
+				x = u32::from_le(din.addrs[fbn]);
+			} else {
+				if u32::from_le(din.addrs[NDIRECT]) == 0 {
+					din.addrs[NDIRECT] = self.freeblock.to_le();
+					self.freeblock += 1;
+				}
+
+				let mut indirect_sector = [0u8; BSIZE];
+				let indirect_blockno = u32::from_le(din.addrs[NDIRECT]);
+				self.rsect(indirect_blockno, &mut indirect_sector);
+
+				let indirect_idx = fbn - NDIRECT;
+				let byte_off = indirect_idx * size_of::<u32>();
+				let mut indirect_entry = u32::from_le(from_bytes::<u32>(
+					&indirect_sector[byte_off..byte_off + size_of::<u32>()],
+				));
+
+				if indirect_entry == 0 {
+					indirect_entry = self.freeblock;
+					self.freeblock += 1;
+					let le = indirect_entry.to_le();
+					indirect_sector[byte_off..byte_off + size_of::<u32>()].copy_from_slice(as_bytes(&le));
+					self.wsect(indirect_blockno, &indirect_sector);
+				}
+
+				x = indirect_entry;
+			}
+
+			let mut buf = [0u8; BSIZE];
+			self.rsect(x, &mut buf);
+
+			let n1 = p
+				.len()
+				.min((fbn as u32 + 1) as usize * BSIZE - off as usize);
+			let block_off = off as usize - (fbn * BSIZE);
+			buf[block_off..block_off + n1].copy_from_slice(&p[..n1]);
+			self.wsect(x, &buf);
+
+			off += n1 as u32;
+			p = &p[n1..];
+		}
+
+		din.size = off.to_le();
+		self.winode(inum, &din);
+	}
+}
+
+fn ipb() -> usize {
+	BSIZE / size_of::<Dinode>()
+}
+
+fn main() {
+	assert_eq!(size_of::<i32>(), 4, "Integers must be 4 bytes");
+	assert_eq!(BSIZE % size_of::<Dinode>(), 0);
+	assert_eq!(BSIZE % size_of::<Dirent>(), 0);
+
+	let mut args = env::args().collect::<Vec<_>>();
+	if args.len() < 2 {
+		eprintln!("Usage: mkfs fs.img files...");
+		std::process::exit(1);
+	}
+
+	let fs_img = args.remove(1);
+
+	let nbitmap = FSSIZE / (BSIZE as u32 * 8) + 1;
+	let ninodeblocks = NINODES / ipb() as u32 + 1;
+	let nlog = LOGSIZE;
+	let nmeta = 2 + nlog + ninodeblocks + nbitmap;
+	let nblocks = FSSIZE - nmeta;
+
+	let sb = Superblock {
+		size: FSSIZE.to_le(),
+		nblocks: nblocks.to_le(),
+		ninodes: NINODES.to_le(),
+		nlog: nlog.to_le(),
+		logstart: 2u32.to_le(),
+		inodestart: (2 + nlog).to_le(),
+		bmapstart: (2 + nlog + ninodeblocks).to_le(),
+	};
+
+	println!(
+		"nmeta {} (boot, super, log blocks {} inode blocks {}, bitmap blocks {}) blocks {} total {}",
+		nmeta, nlog, ninodeblocks, nbitmap, nblocks, FSSIZE
+	);
+
+	let fsfd = OpenOptions::new()
+		.read(true)
+		.write(true)
+		.create(true)
+		.truncate(true)
+		.open(&fs_img)
+		.unwrap_or_else(|e| {
+		eprintln!("{}: {}", fs_img, e);
+		std::process::exit(1);
+	});
+
+	let mut mkfs = Mkfs::new(fsfd, sb, nmeta);
+
+	let zeroes = [0u8; BSIZE];
+	for i in 0..FSSIZE {
+		mkfs.wsect(i, &zeroes);
+	}
+
+	let mut sb_buf = [0u8; BSIZE];
+	sb_buf[..size_of::<Superblock>()].copy_from_slice(as_bytes(&mkfs.sb));
+	mkfs.wsect(1, &sb_buf);
+
+	let rootino = mkfs.ialloc(T_DIR);
+	assert_eq!(rootino, ROOTINO);
+
+	let dot = name_to_dirent(".", rootino as u16);
+	mkfs.iappend(rootino, as_bytes(&dot));
+
+	let dotdot = name_to_dirent("..", rootino as u16);
+	mkfs.iappend(rootino, as_bytes(&dotdot));
+
+	for path in &args[1..] {
+		if path.contains('/') {
+			eprintln!("{}: must be a basename (no /)", path);
+			std::process::exit(1);
+		}
+
+		let mut host_file = File::open(path).unwrap_or_else(|e| {
+			eprintln!("{}: {}", path, e);
+			std::process::exit(1);
+		});
+
+		let file_name = if let Some(stripped) = path.strip_prefix('_') {
+			stripped
+		} else {
+			Path::new(path)
+				.file_name()
+				.and_then(|s| s.to_str())
+				.unwrap_or(path)
+		};
+
+		let inum = mkfs.ialloc(T_FILE);
+		let de = name_to_dirent(file_name, inum as u16);
+		mkfs.iappend(rootino, as_bytes(&de));
+
+		let mut buf = [0u8; BSIZE];
+		loop {
+			let cc = host_file.read(&mut buf).expect("read input file failed");
+			if cc == 0 {
+				break;
+			}
+			mkfs.iappend(inum, &buf[..cc]);
+		}
+	}
+
+	let mut din = mkfs.rinode(rootino);
+	let mut off = u32::from_le(din.size);
+	off = ((off / BSIZE as u32) + 1) * BSIZE as u32;
+	din.size = off.to_le();
+	mkfs.winode(rootino, &din);
+
+	mkfs.balloc(mkfs.freeblock);
+}