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A simple filesystem to understand things. This is a Work In Progress. Do not use this yet. The source files are licensed under Creative Commons Zero License. More information at: http://creativecommons.org/publicdomain/zero/1.0/ Full license text at: http://creativecommons.org/publicdomain/zero/1.0/legalcode Architecture + Notes -------------------- Block Zero = Super block Block One = Inode store Block Two = Occupied by the initial file that is created as part of the mkfs. Only a limited number of filesystem objects are supported. A file cannot grow beyond one block. ENOSPC will be returned as an error on attempting to do. Directories store the children inode number and name in their data blocks. Read support is implemented. Files and Directories can be created. Support for .create and .mkdir is implemented. Basic write support is implemented. Writes may not succeed if done in an offset. Works when you overwrite the entire block. Locks are not well thought-out. The current locking scheme works but needs more analysis + code reviews. Memory leaks may (will ?) exist. Credits -------- All the source code is written by me (Sankar P) until this point. An O_LARGETHANKS to the guidance of VijaiBabu M and Santosh Venugopal. Their excellent talks on filesystems motivated me to implement a file system from the scratch. Without their inspirational speeches, I would not have focussed on filesystems. A big thanks should go to the kernelnewbies mailing list for helping me with clarifying the nitty-gritties of the linux kernel, especially people like Mulyadi Santosa, Valdis Kletnieks, Manish Katiyar, Rajat Sharma etc. Special thanks to Ankit Jain who provides interesting conversations to help my intellectual curiosities. TODO ----- - Check the locks. Remove/Add locks as necessary - Fix the bug related to creation of files in subdirs - Fix various README / TODO comments in the code - Send for review - Make a 1.0 release - After the 1.0 release, start with support for extents, which on completion will be 2.0 - After the 2.0 release, start with journalling support, which on completion will be 3.0 How To ? -------- If you are planning to learn filesystems, start from the scratch. You can look from the first commit in this repository and move the way up. To compile: ------------ install linux kernel sources and run make from the checkedout directory. To test: --------- psankar@linux-9dni:~/src/simplefs> make psankar@linux-9dni:~/src/simplefs> dd bs=4096 count=100 if=/dev/zero of=image 100+0 records in 100+0 records out 409600 bytes (410 kB) copied, 0.00106827 s, 383 MB/s psankar@linux-9dni:~/src/simplefs> ./mkfs-simplefs image Super block written succesfully root directory inode written succesfully welcomefile inode written succesfully inode store padding bytes (after the two inodes) written sucessfully root directory datablocks (name+inode_no pair for welcomefile) written succesfully padding after the rootdirectory children written succesfully welcomefilebody has been written succesfully psankar@linux-9dni:~/src/simplefs> Now as root: linux-9dni:/home/psankar/src/simplefs # insmod simplefs.ko ; mount -o loop -t simplefs image /home/psankar/src/simplefs/mount/ linux-9dni:/home/psankar/src/simplefs # cd mount/ linux-9dni:/home/psankar/src/simplefs/mount # ls vanakkam linux-9dni:/home/psankar/src/simplefs/mount # cat vanakkam Love is God. God is Love. Anbe Murugan. linux-9dni:/home/psankar/src/simplefs/mount # cp vanakkam Hello linux-9dni:/home/psankar/src/simplefs/mount # cat Hello Love is God. God is Love. Anbe Murugan. linux-9dni:/home/psankar/src/simplefs/mount # echo "Hello World" > Hello linux-9dni:/home/psankar/src/simplefs/mount # cat Hello Hello World linux-9dni:/home/psankar/src/simplefs/mount # mkdir dir linux-9dni:/home/psankar/src/simplefs/mount # cd dir linux-9dni:/home/psankar/src/simplefs/mount/dir # cp ../Hello . linux-9dni:/home/psankar/src/simplefs/mount/dir # cat Hello Hello World linux-9dni:/home/psankar/src/simplefs/mount/dir # echo "Vanakkam Ulagam" > Hello linux-9dni:/home/psankar/src/simplefs/mount/dir # cat Hello Vanakkam Ulagam linux-9dni:/home/psankar/src/simplefs/mount/dir # ... linux-9dni:/home/psankar/src/simplefs # umount mount ; rmmod simplefs.ko linux-9dni:/home/psankar/src/simplefs # #Now let us remount and see if all the changes were written to the disk linux-9dni:/home/psankar/src/simplefs # insmod simplefs.ko ; mount -o loop -t simplefs image /home/psankar/src/simplefs/mount/ linux-9dni:/home/psankar/src/simplefs # cd mount/ linux-9dni:/home/psankar/src/simplefs/mount # cat Hello Hello World linux-9dni:/home/psankar/src/simplefs/mount #
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