DUE: Monday 12/9/2024 at 11:59pm ET
All homework submissions are to be made via Git. You must submit a detailed list of references as part of your homework submission indicating clearly what sources you referenced for each homework problem. You do not need to cite the course textbooks and instructional staff. All other sources must be cited. Please edit and include this file in the top-level directory of your homework submission in the main branch of your team repo. Be aware that commits pushed after the deadline will not be considered. Refer to the homework policy section on the class website for further details.
Group programming problems are to be done in your assigned groups. We will let you know when the Git repository for your group has been set up on GitHub. It can be cloned using the following command. Replace teamN with your team number, e.g. team0. You can find your group number here.
$ git clone git@github.com:W4118/f24-hmwk6-teamN.git
This repository will be accessible to all members of your team, and all team members are expected to make local commits and push changes or contributions to GitHub equally. You should become familiar with team-based shared repository Git commands such as git-pull, git-merge, git-fetch. For more information, see this guide.
There should be at least five commits per member in the team’s Git repository. The point is to make incremental changes and use an iterative development cycle. Follow the Linux kernel coding style. You must check your commits with the run_checkpatch.sh script provided as part of your team repository. Errors from the script in your submission will cause a deduction of points. (Note that the script only checks the changes up to your latest commit. Changes in the working tree or staging area will not be checked.)
For students on Arm computers (e.g. macs with M1/M2/M3 CPU): 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 .armpls && git commit -m "Arm pls"
You should do this first so that this file is present in any code you submit for grading.
For all programming problems, you should submit your source code as well as a single README file documenting your files and code for each part. Please do NOT submit kernel images. The README should explain any way in which your solution differs from what was assigned, and any assumptions you made.
For this assignment, the README should explicitly state which parts of the file system assignment were completed successfully and which parts are not functional. It should also state explicitly how each group member contributed to the submission and how many hours each member spent on the homework.
Finally, since this is the last assignment of the semester, EACH group member should indicate at the top of the README five important pieces of information:
The format should be EXACTLY as shown below for each group member:
abc123: 15hrs
difficulty: hmwk1 < hmwk2 < hmwk4 < hmwk6 < hmwk5 < hmwk3
learned: hmwk1 < hmwk2 < hmwk4 < hmwk3 < hmwk5 < hmwk6
rating: 5
comments: any comments here
This would indicate that student with UNI abc123 spent 15 hrs on this assignment, hmwk1 was the easiest and hmwk3 was the hardest, learned the least on hmwk1 and most on hmwk6, 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 the main branch of your team repo. 5% of the grading points for this assignment will be allocated to grading your README.
In this assignment, you will write your own disk-based file system, EZFS. You may find it helpful to first review the EZFS paper. 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 Ubuntu 24.04.1 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.
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 o_o. You should read man pages and search the Internet so you can understand what is going on at each step.
$ sudo su
# dd if=/dev/zero of=./ext2.img bs=1024 count=224
224+0 records in
224+0 records out
229376 bytes (229 kB, 224 KiB) copied, 0.00198087 s, 116 MB/s
# modprobe loop
# losetup --find --show ext2.img
/dev/loop12
# mkfs -t ext2 /dev/loop12
mke2fs 1.47.0 (5-Feb-2023)
Discarding device blocks: done
Creating filesystem with 56 4k blocks and 32 inodes
Allocating group tables: done
Writing inode tables: done
Writing superblocks and filesystem accounting information: done
# mkdir mnt
# mount /dev/loop12 ./mnt
# df -hT
Filesystem Type Size Used Avail Use% Mounted on
...
/dev/loop12 ext2 200K 24K 168K 13% /home/o_o/mnt
# cd mnt
/mnt# ls -al
total 24
drwxr-xr-x 3 root root 4096 Nov 17 19:39 .
drwxr-x--- 24 o_o o_o 4096 Nov 17 19:41 ..
drwx------ 2 root root 16384 Nov 17 19:39 lost+found
/mnt# mkdir sub2
/mnt# ls -al
total 28
drwxr-xr-x 4 root root 4096 Nov 17 19:42 .
drwxr-x--- 24 o_o o_o 4096 Nov 17 19:41 ..
drwx------ 2 root root 16384 Nov 17 19:39 lost+found
drwxr-xr-x 2 root root 4096 Nov 17 19:42 sub2
/mnt# cd sub2
/mnt/sub2# ls -al
total 8
drwxr-xr-x 2 root root 4096 Nov 17 19:42 .
drwxr-xr-x 4 root root 4096 Nov 17 19:42 ..
/mnt/sub2# mkdir sub2.1
/mnt/sub2# ls -al
total 12
drwxr-xr-x 3 root root 4096 Nov 17 19:42 .
drwxr-xr-x 4 root root 4096 Nov 17 19:42 ..
drwxr-xr-x 2 root root 4096 Nov 17 19:42 sub2.1
/mnt/sub2# touch file2.1
/mnt/sub2# ls -al
total 12
drwxr-xr-x 3 root root 4096 Nov 17 19:42 .
drwxr-xr-x 4 root root 4096 Nov 17 19:42 ..
-rw-r--r-- 1 root root 0 Nov 17 19:42 file2.1
drwxr-xr-x 2 root root 4096 Nov 17 19:42 sub2.1
/mnt/sub2# cd ../../
# umount mnt/
# losetup --find
/dev/loop13
# losetup --detach /dev/loop12
# losetup --find
/dev/loop12
# ls -al mnt/
total 8
drwxr-xr-x 2 root root 4096 Nov 17 19:41 .
drwxr-x--- 24 o_o o_o 4096 Nov 17 19:41 ..
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/loop12. Now, /dev/loop12 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/loop12 1000
We have provided you with reference kernel modules that implement EZFS which are designed to work with your stock Ubuntu 24.04.1 kernel (6.8.0-48-amd64 and 6.8.0-48-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/loop12 /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. 6.8.0-49-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.
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 must be contiguous.
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.
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.
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. Also keep in mind that your implemented file system functionality should be compatible with the formatting utility, not the other way around; other than Part 3, you should not change the formatting utility, and certainly should not change it because your file system implementation is not working. 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. Failure to provide the correct naming of your file system will result in an automatic zero on your grade.
Some Hints:
sb_set_blocksize() to ensure that the block layer reads blocks of the correct size.struct ezfs_sb_buffer_heads. Store this struct in the s_fs_info member of the VFS superblock. This way, we can always find the EZFS superblock and inodes by following the trail of pointers from the VFS superblock. EZFS fill_super shows the relationship between these structs after the the superblock is read from disk and its in-memory representation is initialized.iget_locked() to create a new VFS inode for the root directory. Read the kernel source to learn what this function does for you and get some hints on how you’re supposed to use it. The only metadata you need to set is the mode. Make the root directory drwxrwxrwx for now.buffer_heads and dynamically allocated pointers.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.
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: 7,12 Inode: 4 Links: 1
Access: (0000/----------) Uid: (0 / root) Gid: (0 / root)
Access: 2017-03-30 02:42:27.629345430 -0400
Modify: 2017-03-30 02:42:27.629345430 -0400
Change: 2017-03-30 02:42:27.629345430 -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 3 23:31 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.
ls -l and stat.dir_emit() in ezfs_iterate(). Check out this StackOverflow post for why it matters. Hint: you should use S_DT().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 read_folio 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
Emma Nieh
Haruki Gonai
Zijian Zhang
# 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:
cp or rsync.subdir directory./dev/urandom (instead of /dev/zero). Format it. After formatting, the random data should not affect the normal operation of the filesystem.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. In this part, you should also handle writes that shrink files (i.e. the truncate syscall should be supported).
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 writepages called? What’s the benefit of doing so? Referring to BFS’s file.c, implement ezfs_writepages 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 contiguous allocation of blocks to a file, so there are two cases to consider. The easier case is if the data block following the last existing data block of this file is empty, in which case you can allocate this block to it.
$ ls -al /mnt/ez/subdir/
total 52
drwxrwxrwx 2 o_o o_o 4096 Nov 17 19:05 .
drwxrwxrwx 3 o_o o_o 4096 Nov 17 19:05 ..
-rw-rw-rw- 1 o_o o_o 29296 Nov 17 19:05 big_img.jpeg
-rw-rw-rw- 1 o_o o_o 4169 Nov 17 19:05 big_txt.txt
-rw-rw-rw- 1 o_o o_o 38 Nov 17 19:05 names.txt
$ cat /mnt/ez/subdir/big_img.jpeg >> /mnt/ez/subdir/big_txt.txt
$ stat /mnt/ez/subdir/big_txt.txt
File: /mnt/ez/subdir/big_txt.txt
Size: 33465 Blocks: 72 IO Block: 4096 regular file
Device: 7,12 Inode: 6 Links: 1
Access: (0666/-rw-rw-rw-) Uid: ( 1000/ o_o) Gid: ( 1000/ o_o)
Access: 2024-11-17 19:05:19.000000000 -0500
Modify: 2024-11-17 19:07:06.094968851 -0500
Change: 2024-11-17 19:07:06.094968851 -0500
Birth: -
# big_txt.txt's data_block_range change from [14-15] to [14-22]
The harder case is because files are limited to contiguous allocation of data blocks, you should move the existing blocks along with the new block to another position so that there is enough space for the contiguous region of blocks.
# reformat the disk img
$ stat /mnt/ez/hello.txt
File: /mnt/ez/hello.txt
Size: 13 Blocks: 8 IO Block: 4096 regular file
Device: 7,12 Inode: 2 Links: 1
Access: (0666/-rw-rw-rw-) Uid: ( 1000/ o_o) Gid: ( 1000/ o_o)
Access: 2024-11-17 19:05:19.000000000 -0500
Modify: 2024-11-17 19:05:19.000000000 -0500
Change: 2024-11-17 19:05:19.000000000 -0500
Birth: -
$ cat /mnt/ez/subdir/big_txt.txt >> /mnt/ez/hello.txt
$ stat /mnt/ez/hello.txt
File: /mnt/ez/hello.txt
Size: 4182 Blocks: 16 IO Block: 4096 regular file
Device: 7,12 Inode: 2 Links: 1
Access: (0666/-rw-rw-rw-) Uid: ( 1000/ o_o) Gid: ( 1000/ o_o)
Access: 2024-11-17 19:05:19.000000000 -0500
Modify: 2024-11-17 19:10:09.428618497 -0500
Change: 2024-11-17 19:10:09.428618497 -0500
Birth: -
# hello.txt's data_block_range change from [3-3] to [16-17]
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.
Once you can write multi-block files, you should also ensure you can seek to different positions of a file to write data. For example, you should be able to write to the first block of a file, seek 100 blocks ahead and then write to that block of the file. After writing such a file, what should you see when you read the file? Supporting seeking and writing may require additional implementation effort. Note that there is also a zero_blocks bit vector in the EZFS superblock in ezfs.h; if helpful, you may use that for your implementation.
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: 7,12 Inode: 7 Links: 1
Access: (0664/-rw-rw-r--) Uid: ( 1000/ o_o) Gid: ( 1000/ o_o)
Access: 2022-11-16 16:51:03.287875291 -0500
Modify: 2022-11-16 16:51:03.287875291 -0500
Change: 2022-11-16 16:51:03.287875291 -0500
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
Note that the size of an ezfs data block is 4KB, whereas the VFS block size is 512B. When you stat a file, the number of blocks should correspond to the VFS block size. Make sure to correctly convert between the two definitions as needed.
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:
foo.tail -f foo. This command will open foo, print out all the contents, and wait for more lines to be written.cat > foo. This reads from stdin and outputs the result to foo.foo.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 o_o o_o 4096 Nov 16 17:22 ./
drwxr-xr-x 3 root root 4096 Nov 16 17:23 ../
-rw-rw-rw- 1 o_o o_o 13 Nov 16 17:22 hello.txt
drwxrwxrwx 2 o_o o_o 4096 Nov 16 17:22 subdir/
$ mkdir bigtime
$ ls -alF
total 20
drwxrwxrwx 4 o_o o_o 4096 Nov 16 17:23 ./
drwxr-xr-x 3 root root 4096 Nov 16 17:23 ../
drwxr-xr-x 2 o_o o_o 4096 Nov 16 17:23 bigtime/
-rw-rw-rw- 1 o_o o_o 13 Nov 16 17:22 hello.txt
drwxrwxrwx 2 o_o o_o 4096 Nov 16 17:22 subdir/
$ cd bigtime
$ touch tommie
$ ls -alF
total 8
drwxr-xr-x 2 o_o o_o 4096 Nov 16 17:24 ./
drwxrwxrwx 4 o_o o_o 4096 Nov 16 17:23 ../
-rw-r--r-- 1 o_o o_o 0 Nov 16 17:24 tommie
$ cd ..
$ rmdir bigtime
rmdir: failed to remove 'bigtime': Directory not empty
$ ls -alF
total 20
drwxrwxrwx 4 o_o o_o 4096 Nov 16 17:23 ./
drwxr-xr-x 3 root root 4096 Nov 16 17:23 ../
drwxr-xr-x 2 o_o o_o 4096 Nov 16 17:24 bigtime/
-rw-rw-rw- 1 o_o o_o 13 Nov 16 17:22 hello.txt
drwxrwxrwx 2 o_o o_o 4096 Nov 16 17:22 subdir/
$ rm bigtime/tommie
$ rmdir bigtime
$ ls -alF
total 16
drwxrwxrwx 3 o_o o_o 4096 Nov 16 17:25 ./
drwxr-xr-x 3 root root 4096 Nov 16 17:23 ../
-rw-rw-rw- 1 o_o o_o 13 Nov 16 17:22 hello.txt
drwxrwxrwx 2 o_o o_o 4096 Nov 16 17:22 subdir/
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 affect the functionality of the programs you ran?
Include the following in your main branch. Only include source code (ie *.c,*.h) and text files, do not include compiled objects.
.armpls file for teams with M1/M2 CPUsREADME file with additional course evaluation informationreferences.txt fileformat_disk_as_ezfs.cmyez.c and ezfs_ops.h