SLIDE 1
UNRM Hacking the filesystem Jessica Yu WHOOPS... GMAIL: UNDO SEND - - PowerPoint PPT Presentation
UNRM Hacking the filesystem Jessica Yu WHOOPS... GMAIL: UNDO SEND - - PowerPoint PPT Presentation
UNRM Hacking the filesystem Jessica Yu WHOOPS... GMAIL: UNDO SEND unrm operates on the same idea as Gmail's undo send. UNRM: USAGE Goal : after an rm , want to be able to recover all removed files under a certain directory within a set period
SLIDE 2
SLIDE 3
GMAIL: UNDO SEND
unrm operates on the same idea as Gmail's undo send.
SLIDE 4
UNRM: USAGE Goal: after an rm, want to be able to recover all removed files under a certain directory within a set period of time.
$ ls document.pdf image.png file.txt dir/ $ rm -r * # rm all files $ ls -l # all gone! total 0 $ unrm # undo $ ls document.pdf image.png file.txt dir/ # all back!
SLIDE 5
RM: UNDER THE HOOD
Application Application Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
SLIDE 6
RM: UNDER THE HOOD
Application rm Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
$ strace rm file ... unlinkat(AT_FDCWD, "file", 0) ...
SLIDE 7
RM: UNDER THE HOOD
Application rm Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
$ strace rm file ... unlinkat(AT_FDCWD, "file", 0) ... do_unlinkat(...) → vfs_unlink(...)
SLIDE 8
RM: UNDER THE HOOD
Application rm Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
$ strace rm file ... unlinkat(AT_FDCWD, "file", 0) ... do_unlinkat(...) → vfs_unlink(...) → dir->i_op->unlink(...)
SLIDE 9
RM: UNDER THE HOOD
Application rm Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
$ strace rm file ... unlinkat(AT_FDCWD, "file", 0) ... do_unlinkat(...) → vfs_unlink(...) → dir->i_op->unlink(...) → ext4_unlink(....)
SLIDE 10
UNRM: UNDER THE HOOD
Application rm Application C-Standard Library (libc) Virtual Filesystem (VFS) Ext4 Btrfs XFS
USERSPACE KERNELSPACE
What happens during an rm?
$ strace rm file ... unlinkat(AT_FDCWD, "file", 0) ... do_unlinkat(...) → vfs_unlink(...) → dir->i_op->unlink(...) → ext4_unlink(....) → ext4_unrm_save(...)
SLIDE 11
UNRM: OVERVIEW ○ Idea: Intercept unlinking process at the fs layer ○ When we run rm, we want it to look like the file has been removed already ('ls' shouldn't show file) □ But file should still exist somewhere □ And the file is finally removed after a period of time ○ accomplish this via work queues
SLIDE 12
UNRM: OVERVIEW
○ Create a tree
□ "second chance tree" □ radix tree rooted at ext4 superblock info struct ○ indexed by directory inode # □ each node in the tree points to a linked list
○ Linked lists
□ For each directory, use a linked list to keep track
- f individual rm'd files from that dir
○ Work queues
□ Finish unlinking process after set period of time ext4_sb_info
... struct radix_tree_root s_unrm; ... file file file
3 s e c . 3 s e c . 3 s e c .
...
dir 123
SLIDE 13
UNRM: OVERVIEW
○ Create a tree
□ "second chance tree" □ radix tree rooted at ext4 superblock info struct ○ indexed by directory inode # □ each node in the tree points to a linked list
○ Linked lists
□ For each directory, use a linked list to keep track
- f individual rm'd files from that dir
○ Work queues
□ Finish unlinking process after set period of time ext4_sb_info
... struct radix_tree_root s_unrm; ... file file file
R I N G ! ! 3 s e c . 3 s e c .
...
dir 123
SLIDE 14
UNRM: OVERVIEW
○ Create a tree
□ "second chance tree" □ radix tree rooted at ext4 superblock info struct ○ indexed by directory inode # □ each node in the tree points to a linked list
○ Linked lists
□ For each directory, use a linked list to keep track
- f individual rm'd files from that dir
○ Work queues
□ Finish unlinking process after set period of time □ File is removed + entry from linked list removed ext4_sb_info
... struct radix_tree_root s_unrm; ... file file file
3 s e c . 3 s e c .
...
dir 123 goodbye world :(
SLIDE 15
UNRM: OVERVIEW
○ Create a tree
□ "second chance tree" □ radix tree rooted at ext4 superblock info struct ○ indexed by directory inode # □ each node in the tree points to a linked list
○ Linked lists
□ For each directory, use a linked list to keep track
- f individual rm'd files from that dir
○ Work queues
□ Finish unlinking process after set period of time □ File is removed + entry from linked list removed ext4_sb_info
... struct radix_tree_root s_unrm; ... file file
3 s e c . 3 s e c .
...
dir 123
SLIDE 16
UNRM: ext4_unrm_save()
○ Idea: Intercept unlinking process at the fs layer
□ Want to invalidate associated dentry (negate it) ○ So that lookups fail □ ...but keep around the inode secretly (link count > 0) □ keep around the negative dentry too ○ we'll need to "instantiate" it again if we call unrm ○ ...i.e., make the path lookup succeed again!
$ ls testfile testfile: No such file or directory $ ▌
SLIDE 17
UNRM: ext4_unrm_save()
○ Idea: Intercept unlinking process at the fs layer
□ ext4_unlink()
○ Inserts new entry in our radix tree
□ Save relevant info that will let us unrm □ i.e. Save pointers to the inode and dentry
○ But do not drop the inode's i_nlink (# of hard links) ext4_unrm_save():
SLIDE 18
UNRM: ext4_unrm_save()
$ pwd /home/jyu/ $ ls -lih /home/jyu
795 drwx------ 41 jyu jyu 4.0K Aug 12 22:37 /home/jyu
$ ls testfile.pdf track01.mp3 important.doc $ ls -lih testfile.pdf
901 -rw-r--r-- 1 jyu jyu 94K Jun 23 18:04 testfile.pdf
$ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
SLIDE 19
UNRM: ext4_unrm_save()
$ pwd /home/jyu/ $ ls -lih /home/jyu
795 drwx------ 41 jyu jyu 4.0K Aug 12 22:37 /home/jyu
$ ls testfile.pdf track01.mp3 important.doc $ ls -lih testfile.pdf
901 -rw-r--r-- 1 jyu jyu 94K Jun 23 18:04 testfile.pdf
$ rm testfile.pdf $ ▌
radix_tree_root s_unrm
▌ key: 795 ➞ Create a new list
head
➞ Insert into radix
tree with key 795
➞ Create list node
with:
ext4_sb_info
SLIDE 20
UNRM: ext4_unrm_save()
$ pwd /home/jyu/ $ ls -lih /home/jyu
795 drwx------ 41 jyu jyu 4.0K Aug 12 22:37 /home/jyu
$ ls testfile.pdf track01.mp3 important.doc $ ls -lih testfile.pdf
901 -rw-r--r-- 1 jyu jyu 94K Jun 23 18:04 testfile.pdf
$ rm testfile.pdf $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry
➞ Create a new list
head
➞ Insert into radix
tree with key 795
➞ Create list node
with: □ pointer to inode □ pointer to dentry □ allocated work
ext4_sb_info
SLIDE 21
UNRM: ext4_unrm_save()
$ pwd /home/jyu/ $ ls -lih /home/jyu ### inode 795
795 drwx------ 41 jyu jyu 4.0K Aug 12 22:37 /home/jyu
$ ls testfile.pdf track01.mp3 important.doc $ ls -lih testfile.pdf
901 -rw-r--r-- 1 jyu jyu 94K Jun 23 18:04 testfile.pdf
$ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry
➞ Create a new list
head
➞ Insert into radix
tree with key 795
➞ Create list node
with: □ pointer to inode □ pointer to dentry □ allocated work
□ inode 941 □ dentry
ext4_sb_info
SLIDE 22
UNRM: ext4_unrm_save()
$ pwd /home/jyu/ $ ls -lih /home/jyu ### inode 795
795 drwx------ 41 jyu jyu 4.0K Aug 12 22:37 /home/jyu
$ ls testfile.pdf track01.mp3 important.doc $ ls -lih testfile.pdf
901 -rw-r--r-- 1 jyu jyu 94K Jun 23 18:04 testfile.pdf
$ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry
➞ Create a new list
head
➞ Insert into radix
tree with key 795
➞ Create list node
with: □ pointer to inode □ pointer to dentry □ allocated work
➞ Negative dentries
created as unlink process finishes
□ inode 941 □ dentry
ext4_sb_info
SLIDE 23
UNRM: RECURSIVE RM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
SLIDE 24
UNRM: RECURSIVE RM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
SLIDE 25
UNRM: RECURSIVE RM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry
*
inode #'s replaced with filenames for simplicity
SLIDE 26
UNRM: RECURSIVE RM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ echo * testfile.pdf music ### rm -r * uses this order $ rm -r * ### BOOM $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
Mark dir entries so that we can recurse into them when unrm is called later
SLIDE 27
UNRM: RECURSIVE RM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ echo * testfile.pdf music ### rm -r * uses this order $ rm -r * ### BOOM $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
SLIDE 28
UNRM: BACK TO USERSPACE
○ The "unrm" command □ a simple C program ○ issues an ioctl() to ext4 (ext4_ioctl())
○ ext4_ioctl()
ext4_do_unrm()
SLIDE 29
UNRM: ext4_do_unrm()
int ext4_do_unrm(struct super_block *sb, struct inode *dir) Arguments: ○ @sb: superblock struct
□ should be an ext4fs superblock □ from superblock can access our unrm radix tree
○ @dir: directory in which to look for recently rm'd files □ use this dir's inode number as key into radix tree
SLIDE 30
UNRM: ext4_do_unrm()
int ext4_do_unrm(struct super_block *sb, struct inode *dir) What does ext4_do_unrm() do?
○ Lookup dir->i_no with radix_tree_lookup()
□ key: directory inode number. □ entry: linked list of deleted files
○ iterate list of deleted files: list_for_each_entry(...) □ For each deleted file:
○ add the file back to the directory
□
(remember, directories are just files that are lists of other files, so we're technically just adding an entry back)
○ re-instantiate saved dentry with saved inode ○ cancel scheduled work
SLIDE 31
UNRM: ext4_do_unrm()
$ pwd /home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry □ inode 941 □ dentry
ext4_sb_info
SLIDE 32
UNRM: ext4_do_unrm()
$ pwd /home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry □ inode 941 □ dentry
ext4_sb_info
What directory was 'unrm' executed in? ..Oh, /home/jyu, inode 795 Is it in our radix tree?
SLIDE 33
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry □ inode 941 □ dentry
ext4_sb_info
What directory was 'unrm' executed in? ..Oh, /home/jyu, inode 795 Is it in our radix tree? radix_tree_lookup(..,795);
SLIDE 34
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry □ inode 941 □ dentry
ext4_sb_info
What directory was 'unrm' executed in? ..Oh, /home/jyu, inode 795 Is it in our radix tree? radix_tree_lookup(..,795);
SLIDE 35
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 901 □ dentry □ inode 941 □ dentry
ext4_sb_info
radix_tree_lookup(..,795); Found our linked list. Iterate through it: list_for_each_entry(...)
SLIDE 36
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 941 □ dentry
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
□ inode 901 □ dentry
SLIDE 37
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 941 □ dentry
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
SLIDE 38
UNRM: ext4_do_unrm()
$ pwd
/home/jyu
$ ls
testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 941 □ dentry
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
SLIDE 39
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
□ inode 941 □ dentry
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
SLIDE 40
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
SLIDE 41
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌ key: 795
ext4_sb_info
Iterate through it: list_for_each_entry(...) ➞ add inode+dentry back to directory (/home/jyu in this case) ➞ reinstantiate dentry (so it's no longer negative) ➞ cancel scheduled work ➞ remove from list
SLIDE 42
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
List empty, looks like we're all done here.
SLIDE 43
UNRM: ext4_do_unrm()
$ pwd
/home/jyu $ ls testfile.pdf track01.mp3 important.doc $ rm testfile.pdf ### inode 901 $ rm track01.mp3 ### inode 941 $ ls track01.mp3 track01.mp3: No such file or directory $ unrm $ ls ### success! testfile.pdf track01.mp3 important.doc $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
List empty, looks like we're all done here.
SLIDE 44
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
SLIDE 45
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
SLIDE 46
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ testfile.pdf □ dentry □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
SLIDE 47
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
SLIDE 48
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1 hey, it's a directory
SLIDE 49
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1 RECURSE: Grab inode num for music/, recursively call ext4_do_unrm() passing in the ino
SLIDE 50
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1
ext4_do_unrm()
➞ radix_tree_lookup()
➞ found it!
RECURSE: Grab inode num for music/, recursively call ext4_do_unrm() passing in the ino ➞
SLIDE 51
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/ □ track01.mp3 □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1 RECURSE: Grab inode num for music/, recursively call ext4_do_unrm() passing in the ino ➞
SLIDE 52
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry key: music/
*
inode #'s replaced with filenames for simplicity
dir=1 RECURSE: Grab inode num for music/, recursively call ext4_do_unrm() passing in the ino ➞
SLIDE 53
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu □ music/ □ dentry
*
inode #'s replaced with filenames for simplicity
dir=1 RECURSE: Grab inode num for music/, recursively call ext4_do_unrm() passing in the ino ➞
SLIDE 54
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ ▌
radix_tree_root s_unrm
▌
ext4_sb_info
key:/home/jyu
*
inode #'s replaced with filenames for simplicity
➞
SLIDE 55
RECURSIVE UNRM
$ pwd /home/jyu/ $ ls testfile.pdf music/ $ ls music/ track01.mp3 $ rm -r * ### BOOM $ unrm $ tree ### Show dir tree . ├── music ### Hurray! │ └── track01.mp3 └── testfile.pdf
radix_tree_root s_unrm
▌
ext4_sb_info
*
inode #'s replaced with filenames for simplicity
➞ List empty, looks like we're all done here.
SLIDE 56
DEMO
...Let's hope nothing explodes
%_
SLIDE 57
UNRM: ISSUES & FUTURE WORK
○ Warning! unrm is just a fun hack! Was never meant to be used in production With that said...Here are some ideas for future work... ○ Memory hog! Removal of thousands of files = thousands
- f nodes in memory
○ Security - take permissions into account ○ Make work queue delay adjustable - make the period of time adjustable (currently hardcoded at 30 seconds) ○ Filesystem can be left inconsistent in the event of a sudden crash (before unlinking or unrm process finishes) ○ ....probably more! Feel free to send pull requests!
SLIDE 58
FULL KERNEL SOURCE GITHUB.COM/FLAMING-TOAST/UNRM
Thanks!
CONTACT JYU AT EISEN.IO