Introduction to FUSE (File system in USEr space) Speaker:Zong-shuo Jheng Date:March 14, 2008.

Introduction to FUSEIntroduction to FUSE(File system in USEr space)(File system in USEr space)

Speaker: Zong-shuo JhengDate: March 14, 2008

AgendaAgenda

• Brief to VFS (Virtual File System)• FUSE (File system in USEr space)• “Hello world file system” programming tutorial• Demo: a simple fuse file system example

• Why VFS is needed

Brief to VFS (Virtual File System) (1/3)Brief to VFS (Virtual File System) (1/3)

User AP

Ext2/3

FAT32

mount as /mnt/ext2

mount as /mnt/FAT32

#cp /mnt/ext2/data /mnt/FAT32/data

Kernel User AP should know about every IO functions of each file systems to feed the need completing every IO operations.A common interface for user AP to call IO functions is necessary.1. Call ext2_read( ) to get data from /mnt/ext2

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2. Call FAT32_write( ) to write data to /mnt/FAT32

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User spaceKernel space

• How VFS works


User AP

Ext2/3mount as /mnt/ext2

FAT32mount as /mnt/FAT32

#cp /mnt/ext2/data /mnt/FAT32/data

Kernel


VFS

Providing a common interface for every IO functions.

register_filesystem( )


2. Call write( ) to write data to /mnt/FAT32

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1. Call read( ) to get data from /mnt/ext2

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• Issues developers shall address • Hard work for kernel-programming (as drivers)


User AP

Ext2/3mount as /mnt/ext2

FAT32mount as /mnt/FAT32

Kernel


VFS

Special-purposeFile System

ext2_read( )ext2_write( )ext2_open( )

Other necessary IO functions

FAT32_read( )FAT32_write( )FAT32_open( )


NewFS_read( )NewFS_write( )NewFS_open( )


Kernel

VFS

• The role FUSE plays• Programming a file system in user-space

FUSE (File system in USEr space) (1/4)FUSE (File system in USEr space) (1/4)

User AP

Ext2/3

FAT32


FUSE

Kernel

VFS

User-level program

register_filesystem( )FUSE_read( )FUSE_write( )FUSE_open( )

Other necessary IO functions Been implemented by FUSE

Left for developers to complete the IO functions

• How user-level file system works


User AP

Ext2/3

FAT32


FUSE

Kernel

VFS

User-level program

mount as /mnt/user_level_fs

#cat /mnt/user_level_fs/data

1.Call open( ) & read( )2.Bypass the IO call to FUSE module3.Diver the IO call to upper level 4.User-level program open( ) & read( ) are invoked5.Return the result to user AP

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FUSE (File system in USEr space) (3/4)FUSE (File system in USEr space) (3/4)• FUSE-based file system: FTPFS

• Scenario: list the files on the remote FTP server

User AP User spaceKernel space

Kernel

VFS

FTPFSuser-levelprogram

FUSEmount as /mnt/ftpfs


RemoteFTP server

Connection establishUser command: ls /mnt/ftpfs

Bypass to user-level program

FTP command: LSReturn requested data

• How to install FUSE package

• How to build and execute FUSE program


# gcc fuse_example.c –o fuse_example -D_FILE_OFFSET_BITS=64 –lfuse# ./fuse_example /mnt/mount_point

# tar zxvf fuse-2.7.3.tar.gz# cd fuse-2.7.3# ./configure# make# make install

““Hello world file system” programming Hello world file system” programming tutorial (1/)tutorial (1/)

• Main function and function pointers

static struct fuse_operations hello_oper = {.getattr = hello_getattr,.readdir = hello_readdir,.open = hello_open,.read = hello_read,

};

int main(int argc, char *argv[]){

return fuse_main(argc, argv, &hello_oper, NULL);}

Been implemented by developer

IO operations left for developers to implement


static const char *hello_path = "/hello";static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,

off_t offset, struct fuse_file_info *fi){

(void) offset;(void) fi;

if (strcmp(path, "/") != 0)return -ENOENT;

filler(buf, ".", NULL, 0);filler(buf, "..", NULL, 0);filler(buf, hello_path + 1, NULL, 0);

return 0;}

# cd /mnt/mount_pointls getattr( ), access( ), and readdir( )

are called.

Relative path Buffer storing items in directory

. .. hello#

#


# cd /mnt/mount_point#

static const char *hello_path = "/hello";static const char *hello_str = "Hello World!\n";static int hello_read(const char *path, char *buf, size_t size, off_t offset,

struct fuse_file_info *fi){size_t len;(void) fi;if(strcmp(path, hello_path) != 0)

return -ENOENT;len = strlen(hello_str);if (offset < len) {

if (offset + size > len)size = len - offset;

memcpy(buf, hello_str + offset, size);} else

size = 0;return size;

}

cat hello getattr( ), access( ), and read( ) are called.

Relative path Buffer storing read-out data

Hello World!#

Demo: a simple fuse file system exampleDemo: a simple fuse file system example

File system operations interface File system operations interface FUSE specifiedFUSE specified

init destroy statfs mknod createopen read write access lock

truncate ftruncate bmap release fsyncunlink flush mkdir opendir readdir

releasedir rmdir fsyncdir utime utimensrename link symlink readlink getattrfgetattr setxattr getxattr listxattr removexattrchmod chown

init destroy statfs lookup mknodcreate open read write accessbmap getlk setlk release fsyncunlink flush mkdir opendir readdir

releasedir rmdir fsyncdir chmod chownlink symlink readlink getattr setattr

setxattr getxattr listxattr removexattr forget

Common operations:

Low-level operations:

Introduction to FUSE (File system in USEr space) Speaker:Zong-shuo Jheng Date:March 14, 2008.

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Transcript of Introduction to FUSE (File system in USEr space) Speaker:Zong-shuo Jheng Date:March 14, 2008.