Writing flexible filesystems in FUSE-Python

Writing flexible filesystems with

FUSE-Python — Anurag Patel Red Hat, Pune

Also available at

http://xinh.org/fuse-python

Talk overviewUNIX based filesystemsWhat's FUSE?FUSE API overviewToyFSQ&A

On filesystems“One of the real contributions of UNIX has been

the view that everything is a file.”

FilesystemsFS Platform

vfat Windows

hfs+ OS X

ext4 Linux

xfs IRIX, Linux

nfs Linux*

iso9660 CD-ROM

fuse Linux*

# cat /proc/filesystems

FilesSymbol Meaning

d Directory

l Symbolic link

c Character device

b Block device

s Socket

p Named pipe

- Regular file

FUSEFilesystem in USErspace

Virtual memory segregation

Why FUSE?Usable by unprivileged usersEasier development cycleEasy to install (apt-get install sshfs)Multiple language support and bindingsC, C++, Python, Java, Ruby, Perl, Golang, LuaPorted to FreeBSD, Mac OSX, OpenSolaris

FUSE overview

How do I install FUSE?# yum install fuse fuse-python

# apt-get install fuse python-fuse

Loading fuse# modprobe fuse

# lsmod | grep fuse

Filesystem classSubclass fuse.Fuse class and implement a

number of methods.

Mount filesystemInstantiate the Filesystem class and call main()

mount$ python toyfs.py /tmp/toy

getattr(path)Defining this method is mandatory for a working filesystem.

The stat structureMember Description

st_mode Inode protection mode

st_ino File serial number

st_dev Device ID

st_nlink Number of hard links

st_uid User ID of file

st_gid Group ID of file

st_size File size in bytes

st_atime Time of last access

st_mtime Time of last data modification

st_ctime Time of last status change

ref: <sys/stat.h>

$ stat /etc/fstab[anurag@zomg toyfs]$ stat /etc/fstab File: ‘/etc/fstab’ Size: 481 Blocks: 8 IO Block: 4096 regular fileDevice: fd01h/64769d Inode: 259076 Links: 1Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)Context: system_u:object_r:etc_t:s0Access: 2015-02-20 14:46:16.248920273 +0530Modify: 2015-02-11 20:42:51.750210844 +0530Change: 2015-02-11 21:56:52.520767293 +0530 Birth: -[anurag@zomg toyfs]$

st_modest.st_mode = stat.S_IFDIR | 0755

Each bit of the output is 0 if the corresponding bitof x AND of y is 0, otherwise it's 1

ST_MODE flagsType Flag

d stat.S_IFDIR

l stat.S_IFLNK

c stat.S_IFCHR

b stat.S_IFBLK

s stat.S_IFSOCK

p stat.S_IFIFO

- stat.S_IFREG

ref: Python stat module

readdir(path)Read directory contents

Reading filesopen(path, flags)

read(path, length, offset)

Filesystem methodsGeneral File operation

getattr(path) open(path, flags)

mkdir(path, mode) create(path, flags, mode)

rename(old, new) read(path, length, offset)

mknod(path, mode, rdev) write(path, buf, offset)

link(target, name) fgetattr(path)

symlink(target, name) ftruncate(path, len)

readlink(path) flush(path)

unlink(path) release(path)

fsinit(self) fsync(path, fdatasync)

FUSE filesystemsfuse-zip, rarfs, mysqlfs, cryptfs, httpfs, sshfs,

imapfs, gmailfs, flickrfs, ntfs-3g, gitfs, and manymany more...

THE END

ToyFS on Github →FUSE Project →

FUSE Python reference →

— @gnurag [email protected]