ezfs

EZFS

Red Pokemon
Gotta File 'Em All: Managing Your Pokémon Data with Precision!

Submission

As with previous assignments, we will be using GitHub to distribute skeleton code and collect submissions. Please refer to our Git Workflow guide for more details. Note that we will be using multiple tags for this assignment, for each deliverable part.

For students on arm64 computers (e.g. M1/M2/M3 machines): if you want your submission to be built/tested for ARM, you must create and submit a file called .armpls in the top-level directory of your repo; feel free to use the following one-liner:

cd "$(git rev-parse --show-toplevel)" && touch .armpls && git add -f .armpls && git commit .armpls -m "ARM pls"

You should do this first so that this file is present in all parts.

Mandatory Survey

Since this is the last assignment of the semester, EACH group member should indicate in the README five important pieces of information:

  1. The number of hours spent on this assignment
  2. A rank ordering of the difficulty of the homework assignments
  3. A rank ordering of how much you learned on each homework assignment
  4. The extent to which you agree that this assignment has significantly improved your understanding of file systems (1=strongly disagree, 2=disagree, 3=neutral, 4=agree, 5=strongly agree)
  5. Any comments about your how your educational experience doing this assignment. The format should be EXACTLY as shown below for each group member:

Here’s a recap of this semester’s homework

For example,

abc123: 15hrs

difficulty: Linux-List < Multi-Server < EZFS < Fridge < Farfetch < Freezer < Tabletop

learned: Multi-Server < Linux-List < Tabletop < EZFS < Farfetch < Freezer < Fridge

rating: 5

comments: any comments here

would indicate that student with UNI abc123 spent 15 hrs on this assignment and that Linux-List was the easiest and Tabletop was the hardest, learned the least on Multi-Server and most on Fridge, and strongly agree that this assignment significantly improved abc123’s understanding of file systems. The README should be placed in the top level directory of your team repo. 5 points for this assignment will be allocated to grading your README.

Code Style

There is a script in the skeleton code named run_checkpatch.sh. It is a wrapper over linux/scripts/checkpatch.pl, which is a Perl script that comes with the linux kernel that checks if your code conforms to the kernel coding style.

Execute run_checkpatch.sh to see if your code conforms to the kernel style – it’ll let you know what changes you should make. You must make these changes before pushing a tag. Passing run_checkpatch.sh with no warnings and no errors is required for this assignment.

Overview

In this assignment, you will write your own disk-based file system, EZFS. You will learn how to use a loop device to turn a regular file into a block storage device, then format that device into an EZFS file system. Then you will use EZFS to access the file system. EZFS will be built as a kernel module that you can load into the stock Debian 11.6 kernel in your VM. You do NOT need to use the 4118 kernel you built for previous homework assignments and there is no need to build the entire Linux kernel tree for this assignment.

Part 1: Formatting and mounting disks

A loop device is a pseudo-device that makes a file accessible as a block device. Files of this kind are often used for CD ISO images. Mounting a file containing a file system via such a loop mount makes the files within that file system accessible. You will do this with EZFS, but to first gain some experience with a loop device, the following gives you a sample session for creating a loop device and building and mounting an ext2 file system on it. This session starts from the home directory of a user alex. You should read man pages and search the Internet so you can understand what is going on at each step.

~$ uname -a
Linux albian 5.10.0-27-arm64 #1 SMP Debian 5.10.205-2 (2023-12-31) aarch64 GNU/Linux
~$ sudo su
/home/alex# cd ~
~# dd if=/dev/zero of=./ext2.img bs=1024 count=100
100+0 records in
100+0 records out
102400 bytes (102 kB, 100 KiB) copied, 0.000365627 s, 280 MB/s
~# modprobe loop
~# losetup --find --show ext2.img
/dev/loop0
~# mkfs -t ext2 /dev/loop0
mke2fs 1.46.2 (28-Feb-2021)
Creating filesystem with 100 1k blocks and 16 inodes

Allocating group tables: done                            
Writing inode tables: done                            
Writing superblocks and filesystem accounting information: done

~# mkdir mnt
~# mount /dev/loop0 ./mnt
~# df -hT
Filesystem     Type      Size  Used Avail Use% Mounted on
...
/dev/loop0     ext2       93K   14K   74K  16% /root/mnt
~# cd mnt
~/mnt# ls -al
total 17
drwxr-xr-x 3 root root  1024 Apr 19 20:57 .
drwx------ 6 root root  4096 Apr 19 20:57 ..
drwx------ 2 root root 12288 Apr 19 20:57 lost+found
~/mnt# mkdir sub2
~/mnt# ls -al
total 18
drwxr-xr-x 4 root root  1024 Apr 19 20:58 .
drwx------ 6 root root  4096 Apr 19 20:57 ..
drwx------ 2 root root 12288 Apr 19 20:57 lost+found
drwxr-xr-x 2 root root  1024 Apr 19 20:58 sub2
~/mnt# cd sub2
~/mnt/sub2# ls -al
total 2
drwxr-xr-x 2 root root 1024 Apr 19 20:58 .
drwxr-xr-x 4 root root 1024 Apr 19 20:58 ..
~/mnt/sub2# mkdir sub2.1
~/mnt/sub2# ls -al
total 3
drwxr-xr-x 3 root root 1024 Apr 19 20:58 .
drwxr-xr-x 4 root root 1024 Apr 19 20:58 ..
drwxr-xr-x 2 root root 1024 Apr 19 20:58 sub2.1
~/mnt/sub2# touch file2.1
~/mnt/sub2# ls -al
total 3
drwxr-xr-x 3 root root 1024 Apr 19 20:58 .
drwxr-xr-x 4 root root 1024 Apr 19 20:58 ..
-rw-r--r-- 1 root root    0 Apr 19 20:58 file2.1
drwxr-xr-x 2 root root 1024 Apr 19 20:58 sub2.1
~/mnt/sub2# cd ../../
~# umount mnt/
~# losetup --find
/dev/loop1
~# losetup --detach /dev/loop0
~# losetup --find
/dev/loop0
~# ls -al mnt/
total 8
drwxr-xr-x 2 root root 4096 Apr 19 20:57 .
drwx------ 6 root root 4096 Apr 19 20:57 ..
~# 
exit

In the sample session shown above, files and directories are created. Make sure you see the number of links each file or directory has, and make sure you understand why.

Also try creating some hard links and symlinks. Make sure you understand how they affect the link counts.

Part 2: Exploring EZFS

Now that you understand how to use a loop device, mount a loop device and format it as EZFS. To do the latter, we have provided you with source code for an EZFS formatting program. First create a disk image and assign it to a loop device:

$ dd bs=4096 count=1000 if=/dev/zero of=~/ez_disk.img
# losetup --find --show ~/ez_disk.img

This will create the file ez_disk.img and bind it to an available loop device, probably /dev/loop0. Now, /dev/loop0 can be used as if it were a physical disk, and the data backing it will be stored in ez_disk.img.

Now format the disk as EZFS. The skeleton code for a formatting utility program is in format_disk_as_ezfs.c. Compile it, then run it:

# ./format_disk_as_ezfs /dev/loop0 1000

We have provided you with reference kernel modules that implement EZFS, which are designed to work with your stock Debian 11 kernel (5.10.205-amd64 and 5.10.205-arm64). x86 and arm kernel modules are in ref/ez-x86.ko and ref/ez-arm.ko, respectively. You should familiarize yourself with writing and using Linux kernel modules. You can use the reference kernel module to explore your newly created EZFS by mounting the disk and loading the kernel module:

# mkdir /mnt/ez
# insmod ez-ARCH.ko
# mount -t ezfs /dev/loop0 /mnt/ez

where ARCH is either x86 or arm. Now you can create some new files, edit hello.txt, etc. If your kernel name is slightly different (e.g. 5.10.205-amd64), you may get a versioning error when you try to load the kernel module. In that case, you can try forcibly inserting the module with insmod -f.

Part 3: Changing the formatting program

The formatting utility creates the new file system’s root directory and places hello.txt in that directory. You can think of the formatting utility as statically creating the file system on a disk. You will first create directories and files by modifying the formatting utility, as this will help you later to figure out what EZFS must do to perform these file system operations. Start by reviewing the EZFS specification, then read the formatting utility source code format_disk_as_ezfs.c. Make sure you understand the on-disk format and what each line contributes toward creating the file system. A key simplifying concept in EZFS is how file data is stored, specifically directories are limited to one block in size and regular files may use multiple blocks but the blocks used for storing the data for a given file are managed using a simple index allocation scheme with a single direct block and a single indirect block. Since EZFS blocks are 4KB, this means that your maximum file size is slightly more than 2MB.

The entries in your indirect block should simply be uint64_t stored block numbers. A 4KB indirect block should therefore contain 512 uint64_t entries. Entries that are not in use should be zeroed. You should also use zero to denote entries that are not in use for your inodes. In other words, if either the direct or indirect block entry in the inode are not used, the respective entry should be zeroed.

Now extend the formatting utility program to create a subdirectory called subdir. The directory should contain names.txt that lists the names of your team members, big_img.jpeg, and big_txt.txt. The latter two files are in your repo subdirectory big_files/. names.txt should be stored in disk block number 5, big_img.jpeg in disk block numbers 6-13, and big_txt.txt in disk block numbers 14-15. Be sure to set the directories’ link counts correctly. Any required indirect blocks can be placed in any free disk block and are not included in the disk block numbers listed above. For example, big_txt.txt will require an additional disk block for its indirect block in addition to disk block numbers 14-15 for its data.

Create and format a new disk using your modified program. Use the reference EZFS kernel module provided to verify that the new files and directory were created correctly. You can use the stat command to see the size, inode number, and other properties. Note that the primary purpose of the reference EZFS kernel module is to provide a way to check that your formatting utility program operates correctly. It does not necessarily implement all of the functionality that you will provide in your own EZFS implementation.

Part 4: Initializing and mounting the file system

Now that you understand how to manually add files to your file system via your formatting utility, you will now write a file system to allow you to use standard file commands mount the file system, list directories, read files, modify existing files, create new files, delete files, and even create and remove directories. The rest of this assignment is structured to guide you toward incrementally implementing your file system functionality, which you will do by implementing ez_ops.h and myez.c in your team repo. In some cases, you may find that what you implemented is correct enough to get some piece of functionality working, but may not be completely correct such that some later functionality that depends on it ends up not working. Keep that in mind during your debugging. Here are some resources that might be useful, though keep in mind that some of the information contained therein may be out of date:

Note that the VFS has evolved over the years and some functions exist primarily for backwards compatibility with older file system implementations. In your implementation, you should make sure to use the newer VFS interface functions discussed in class whenever possible. As always, the best source of correct information is the source code, especially other file system implementations, some of which were described in class, including ramfs. Other file system implementations are also good references to see what functions you have to implement and which ones you do not have to implement, or can implement by leveraging functions already provided by the VFS.

This part of the assignment focuses on writing the code that initializes the file system and enables mounting disks. Create the basic functionality for your file system to work as a kernel module so that it can be loaded and unloaded from the kernel. Then make the mount and umount commands work cleanly. We won’t be reading any files or directories at this time.

The name attribute of your struct file_system_type MUST BE myezfs or ezfs. Failure to provide the correct naming of your file system will result in an automatic zero on your grade.

Some Hints:

Part 5: Listing the contents of the root directory

In the previous part, you may have created a VFS inode without associating it with the corresponding EZFS inode from disk. Although this may be sufficient for mount to work, it will not be enough to properly list the contents of the root directory. You need to update your code to associate the root VFS inode with the root EZFS inode. Use the i_private member of the VFS inode to store a pointer to the EZFS inode. All of the EZFS inodes live in the inode store that we read from disk in the previous section. Consult the diagram in the EZFS Specification section.

Now you can add support for listing the root directory. You should be able to run ls and ls -a. Note that we do not support listing the contents of a subdirectory yet. Here’s sample session:

# ls /mnt/ez
hello.txt  subdir
# ls -a /mnt/ez
.  ..  hello.txt  subdir
# ls /mnt/ez/subdir
ls: cannot access '/mnt/ez/subdir': No such file or directory

The VFS framework will call the iterate_shared member of the struct file_operations. Inside your iterate_shared implementation, use dir_emit() to provide VFS with the contents of the requested directory. VFS will continue to call iterate_shared until your implementation returns without calling dir_emit(). Make sure you implement iterate_shared, not iterate, as the latter is an older interface. For now, you can pass in DT_UNKNOWN as the type argument for dir_emit(). We will revisit this in the next part. You can use the ctx->pos variable as a cursor to the directory entry that you are about to emit. Note that iterating through a directory using dir_emit() will list each directory entry contained in the directory, but what should be done to cause the . and .. to appear in the listing? Some file systems accomplish this by actually storing separate entries for . and .. so that they will appear just like any other entry, but other file systems do not, such as the proc file system. Look at how the proc file system achieves this behavior, and use a similar approach for your EZFS.

The following is an excerpt from the output of strace ls /usr/bin > /dev/null:

[...]
openat(AT_FDCWD, "/usr/bin", O_RDONLY|O_NONBLOCK|...) = 3
[...]
getdents64(3, /* 1003 entries */, 32768) = 32744
[...]
getdents64(3, /* 270 entries */, 32768) = 8888
[...]
getdents64(3, /* 0 entries */, 32768)   = 0
close(3)                                = 0

The ls program first opens the /usr/bin directory file. Then, it calls getdents64() three times to retrieve the list of 1,273 files in /usr/bin. Finally, ls closes the directory file. Each call to getdents64() will result in one call to iterate_dir(), which in turn will call your iterate_shared implementation. Consequently, your iterate_shared implementation should call dir_emit() until the given buffer is full.

Running ls -l might print error messages because the ls program is unable to stat the files. This is the expected behavior for this part.

Part 6: Accessing subdirectories

Add support for looking up filepaths. You should be able to cd into directories and ls the contents of directories that aren’t the root. As a side effect, the -l flag and stat command should work on both files and directories now. Here’s a sample session:


# ls /mnt/ez/subdir
    names.txt
# cd /mnt/ez/subdir
# stat names.txt
  File: names.txt
  Size: 0         	Blocks: 0          IO Block: 4096   regular empty file
Device: 700h/1792d	Inode: 4           Links: 1
Access: (0000/----------)  Uid: (0 /    root)   Gid: (0 /    root)
Access: 2024-04-19 22:57:51.953272062 -0400
Modify: 2024-04-19 22:57:51.953272062 -0400
Change: 2024-04-19 22:57:51.953272062 -0400
 Birth: -
# stat does_not_exist.txt
stat: cannot stat 'does_not_exist.txt': No such file or directory
# ls -l ..
total 0
---------- 1 root root 0 Apr 19 22:54 hello.txt
d--------- 1 root root 0 Dec 31  1969 subdir

VFS does most of the heavy lifting when looking up a filepath. To avoid repeated work when looking up similar paths, the kernel maintains a cache called the dentry cache. Learn how the dentry cache works by reading the materials given earlier. A given path is split up into parts and each part is looked up in the dentry cache. If a part isn’t in the dentry cache, the VFS will call the file system-specific lookup function of inode_operations to ask the file system to add it. For example, given a filepath such as /a/b/c/d/e/f.txt, once the kernel knows the inode of c, it will ask for the inode associated with the name d in the directory c. If there is no matching dentry in the cache, the lookup function will be called to retrieve the inode for d from the filesystem. Before you add things to the dentry cache, you are responsible for determining whether the given parent directory contains an entry with the given name.

Make sure your code returns correct metadata for all files and directories. These include size, link count, timestamps, permissions, owner, and group.

Test by using ls -l and stat. You should also pass the correct type to dir_emit() in ezfs_iterate(). Check out this StackOverflow post for why it matters. Hint: you should use S_DT().

Part 7: Reading the contents of regular files

Add support for reading the contents of files. There are a number of ways to do this, but you should take advantage of generic functions that are already available as part of the VFS to implement read_iter, not read. For example, generic_file_read_iter handles complex logic to read ahead so that file blocks can be cached in memory by the time they are actually needed to avoid blocking on slow I/O devices. However, generic file system functions are unaware of file system-specific functionality for deciding what data blocks are actually associated with each file, so the job of the file system is to provide that information through appropriate functions that will be called by the generic functions. You should read generic_file_read_iter to understand how it interacts with address_space_operations to see what functions need to be implemented. Hint: what is readpage and how is it used? You may find it particularly helpful to refer to the BFS file system, specifically file.c. What is the functionality or magic of map_bh? Once you have read support, you should be able to do the following:

# cat /mnt/ez/hello.txt
Hello world!
# cat /mnt/ez/subdir/names.txt
Kostis Kaffes
Abhinav Gupta
Jiakai Xu
# dd if=/mnt/ez/hello.txt
Hello world!
0+1 records in
0+1 records out
13 bytes copied, 4.5167e-05 s, 266 kB/s
# dd if=/mnt/ez/hello.txt bs=1 skip=6
world!
7+0 records in
7+0 records out
7 bytes copied, 5.1431e-05 s, 117 kB/s

If you try using other programs to read files, you may encounter some errors. For example, vim by default places swap files in the current directory and seeks through them upon opening a file using llseek. You may have noticed an error when trying to open files using vim because your EZFS has no support for llseek yet. Fix it. Hint: there’s already a generic implementation in the kernel for llseek.

At this point, you should stress test your EZFS implementation. The rest of this assignment will be easier if you can depend on the reading functionality to report things correctly. Some of the things you should make sure work include:

Part 8: Writing to existing files

So far, we’ve only been reading what’s already on the filesystem. Implement functions for modifying the filesystem contents. Again, you should implement write_iter instead of write. Read generic_file_write_iter, try to understand how it helps us to write iteratively, and find out how it interacts with address_space_operations. Do we need to worry about changing the length of the file ourselves? How about time accounting and inode->i_blocks? It seems that only write_begin and write_end are called in generic_file_write_iter. When is writepage called? What’s the benefit of doing so? Referring to BFS’s file.c, implement ezfs_writepage and ezfs_write_begin. We recommend you first make sure your write functionality works for a file that requires no more than one data block for its contents. Test for writing the contents of files:

$ cd /mnt/ez
$ echo -ne "4118" | dd of=hello.txt bs=1 seek=7 conv=notrunc
[...]
$ cat hello.txt
Hello w4118!
$ echo "Greetings and salutations, w4118!" | dd of=hello.txt conv=notrunc
[...]
$ cat hello.txt
Greetings and salutations, w4118!

Once you have the one block case working, then you should consider what if the file requires more than one block. EZFS only supports index allocation of blocks to a file. As indicated above, the entries in your indirect block should simply be uint64_t stored block numbers. Indirect block entries that are not in use should be zeroed. If either the direct or indirect block entry in the inode are not used, the respective entry should also be zeroed. You should also be able to edit files with the nano editor, although it will complain about fsync() not being implemented. Fix this problem.

Ensure that changes to the VFS inode are written back to disk. You should do this by implementing ezfs_write_inode(). Of course, VFS needs to be informed that the VFS inode is out of sync with the EZFS inode. Test this by unmounting and remounting. Writing to the buffer head only changes the contents in memory. It does not cause those changes to be written back to disk. Be sure to take the appropriate measures so that your modifications are written to disk.

If there is not enough space in your file system to write what you need to write, you should return an appropriate error, specifically ENOSPC. Keep in mind that there may be multiple reasons why there is not enough space.

Until you introduced writing files, you were not really modifying your file system. Now that the file system is being modified, you should take care to make sure that concurrent file operations are being handled properly, if you have not done so already. For example, if two files are being modified at the same time, you want to make sure that you do not accidentally assign the same free data block to both files, which would obviously be an error. Make sure that your EZFS operations work properly when multiple processes or threads are performing those operations at any given time. Keep in mind that buffer head operations such as sb_bread may block if they need to go to disk. You may find it helpful to review how synchronization is handled in BFS.

Part 9: Creating new files

Implement creating new files. That is, user programs should be able to call open() with a mode that includes ‘O_CREAT’. Note that an empty file should have 0 data blocks. Here’s a sample session:

$ cd /mnt/ez
$ ls
hello.txt  subdir
$ touch world.txt
$ ls
hello.txt  subdir  world.txt
$ stat world.txt
  File: world.txt
  Size: 0         	Blocks: 0          IO Block: 4096   regular empty file
Device: 700h/1792d	Inode: 7           Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/    alex)   Gid: ( 1000/    alex)
Access: 2024-04-19 23:03:14.195621482 -0400
Modify: 2024-04-19 23:03:14.195621482 -0400
Change: 2024-04-19 23:03:14.195621482 -0400
 Birth: -
$ cat > subdir/favorite_memes.txt
doge
chad
BigTime Tommie
https://youtu.be/TiC8pig6PGE  # Ctrl+D to denote EOF
$ cat subdir/favorite_memes.txt
doge
chad
BigTime Tommie
https://youtu.be/TiC8pig6PGE

Part 10: Deleting files

While testing the previous part, you probably created lots of files that are now cluttering your disk. Let’s implement a way to delete those files. Review how the VFS dentry and inode caches interact with each other using the resources given earlier in this assignment. Implement the unlink and evict_inode ops so that you can delete files.

You are not required to implement directory removal in this part, that will happen in the next part. Ensure that you are reclaiming data blocks and EZFS inodes when appropriate. To test this, see if you can repeatedly create and remove files.

for i in {1..10}; do touch {1..14}; rm {1..14}; done

In a Unix-like operating system, what is the correct behavior if one process unlinks a file while another process has the same file open? Here’s an experiment you can run on ext4 or the EZFS reference implementation to find out:

Part 11: Making and removing directories

Implement creating new directories. That is, user programs should be able to call mkdir(). This should be very similar to what you did to support creating regular files. You need to make sure that you’re setting a size and link count appropriate for a directory, rather than a regular file. Hint: consider the link count of the parent directory of the newly created directory as well. In this part as well as the preceding ones, you should make sure that whatever robustness tests you did earlier continue to pass.

Implement deleting directories. User programs should be able to call rmdir() successfully on empty directories. This should be very similar to what you did in the previous part. Take a look at simple_rmdir() for some additional directory-specific steps. Note that simple_empty() is not sufficient to check if a directory is empty for our purposes, because the function simply checks the dentry cache to see if a directory has children. Can you think of a case where this would lead to incorrect behavior?

Here’s a sample session:

$ ls -alF
total 16
drwxrwxrwx 3 alex alex 4096 Apr 19 23:10 ./
drwxr-xr-x 3 root root 4096 Apr 19 23:10 ../
-rw-rw-rw- 1 alex alex   13 Apr 19 23:10 hello.txt
drwxrwxrwx 2 alex alex 4096 Apr 19 23:10 subdir/
$ mkdir bigtime
$ ls -alF
total 20
drwxrwxrwx 4 alex alex 4096 Apr 19 23:12 ./
drwxr-xr-x 3 root root 4096 Apr 19 23:10 ../
drwxr-xr-x 2 alex alex 4096 Apr 19 23:12 bigtime/
-rw-rw-rw- 1 alex alex   13 Apr 19 23:10 hello.txt
drwxrwxrwx 2 alex alex 4096 Apr 19 23:10 subdir/
$ cd bigtime
$ touch tommie
$ ls -alF
total 8
drwxr-xr-x 2 alex alex 4096 Apr 19 23:13 ./
drwxrwxrwx 4 alex alex 4096 Apr 19 23:12 ../
-rw-r--r-- 1 alex alex    0 Apr 19 23:13 tommie
$ cd ..
$ rmdir bigtime
rmdir: failed to remove 'bigtime': Directory not empty
$ ls -alF
total 20
drwxrwxrwx 4 alex alex 4096 Apr 19 23:13 ./
drwxr-xr-x 3 root root 4096 Apr 19 23:10 ../
drwxr-xr-x 2 alex alex 4096 Apr 19 23:13 bigtime/
-rw-rw-rw- 1 alex alex   13 Apr 19 23:10 hello.txt
drwxrwxrwx 2 alex alex 4096 Apr 19 23:10 subdir/
$ rm bigtime/tommie
$ rmdir bigtime
$ ls -alF
total 16
drwxrwxrwx 3 alex alex 4096 Apr 19 23:14 ./
drwxr-xr-x 3 root root 4096 Apr 19 23:10 ../
-rw-rw-rw- 1 alex alex   13 Apr 19 23:10 hello.txt
drwxrwxrwx 2 alex alex 4096 Apr 19 23:10 subdir/

Part 12: Compile and run executable files

Compiling and running executable files requires some additional functionality beyond what you have already implemented, specifically support for mmap. Given the approach you should have taken thus far, implementing mmap support should be trivial. Do it. At this point, you should now be able to compile and execute programs. This part will also double verify that you implemented the functionality of “read/write/fsync”, “create/delete” correctly.

Here’s a sample session:

$ cd /mnt/ez
$ vim test.c
$ ls
hello.txt  subdir  test.c
$ cat test.c
#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}
$ gcc test.c
$ ls
a.out  hello.txt  subdir  test.c
$ ./a.out
Hello, World!

At this point, you should make sure that whatever robustness tests you did earlier continue to pass with your completed file system, and your tests should include having multiple processes or threads perform various file system operations concurrently. In addition, you should try running various programs manipulating the files in your file system. You should also make sure you test by unmounting and remounting to make sure all your programs manipulating files work correctly with the file data actually written to disk and not just file data in the page cache. In your README, note which applications you have used, which ones worked, and which ones do not. What are some file operations supported on your default Linux file system that are not supported by EZFS? Which of these affects the functionality of the programs you ran?

Submission

At this point, you should make sure that whatever robustness tests you did earlier continue to pass with your completed file system, and your tests should include having multiple processes or threads perform various file system operations concurrently. In addition, you should try running various programs manipulating the files in your file system.

To submit this part, push the hw8handin tag with the following:

$ git tag -a -m "Completed hw8." hw8handin
$ git push origin main
$ git push origin hw8handin

Acknowledgment

The ezFS assignment and reference implementation were designed and implemented by the following TAs of COMS W4118 Operating Systems I, Fall 2022, Columbia University:

It was incorporated by the following TAs in the Spring 2024 offering of Operating Systems I taught by Prof. Kostis Kaffes:

Last updated: 2024-04-26