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Вы можете ознакомиться и скачать презентацию на тему WritingFS4Fun. Доклад-сообщение содержит 21 слайдов. Презентации для любого класса можно скачать бесплатно. Если материал и наш сайт презентаций Mypresentation Вам понравились – поделитесь им с друзьями с помощью социальных кнопок и добавьте в закладки в своем браузере.

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Writing Linux FS 4 FUN

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Outline Why Main Concepts and bit of history Earlier design decisions On disk layout Implementing own FS On disk layout Code Fragments: Kernel Implementation Other tools mkfs, fsdb

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Why this talk?! Cons Writing FS is quite time consuming (approx. 10 years…) Just few production ready FS, many abandoned or not truly maintained Pros Learning: Address specific gap Solving other complicated problems Storage stack is complicated and usually became a bottleneck Data is foundation of most todays application

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Early days: 6th ed. of UNIX File system: one internal component of the kernel Not possible to use other FS Block size as fixed 512 bytes Possible indirect block (up to 3 level depth) Max size of file: 32*32*32 data blocks

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$Early days: 6th ed. of UNIX struct inode { i_mode // file type* i_nlink // nr of hard links i_uid i_gid i_size i_addr[7] // 7 pointers to blocks...$

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Early days: 6th ed. of UNIX struct inode { i_mode // file type* i_nlink // nr of hard links i_uid i_gid i_size i_addr[7] // 7 pointers to blocks i_mtime // modify time i_atime // access time }

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File System Switch

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SunOS VFS/vnode

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On Disk Layout: UFS Initial UNIX FS has poor performance UFS new design concerned the layout of data on disks i.e: Track contains same amount of data The old UNIX FS was only able to use 3 to 5 percent of the disk bandwidth while the FFS up to 47 percent of the disk bandwidth*

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On Disk layout: EXT2 EXT2 divide filesystem to number of block groups inode allocation done during mkfs Fixed offset for first Block Group, space for bootloader

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Sample implementation dummyfs Implemented as in kernel module (possible to implement in user space using FuseFS) Provide basic functionality necessary to mount read write files to the disk Pseudo modern on disk layout Good starting point to learn internal/implementing more advanced features Not using kernel caching mechanisms

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Inode structures:

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On Disk layout Simple but not trivial Inode table and Inode bitmap are ‘files’ which allow them to scale Blocks addresses are 32 bit integers which define limits

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Basic components: Main implementation of specific components in dir.c file.c inode.c super.c Structures inside dummy_fs.h shared by kernel and user space components Module implementation in dummyfs.c: registration of FS, allocate memory for inodes

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$In-Core structures struct dm_inode { u8 i_version; u8 i_flags; u32 i_mode; u32 i_ino; u16 i_uid; u32 i_ctime; u32 i_mtime; u32 i_size; u32...$

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In-Core structures struct dm_inode { u8 i_version; u8 i_flags; u32 i_mode; u32 i_ino; u16 i_uid; u32 i_ctime; u32 i_mtime; u32 i_size; u32 i_addrb[DM_EXT_SIZE]; u32 i_addre[DM_EXT_SIZE]; };

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$Fragments: Mount // mount process: struct file_system_type dummyfs_type = { .name = "dummyfs", .mount = dummyfs_mount, .kill_sb =...$

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Fragments: Mount // mount process: struct file_system_type dummyfs_type = { .name = "dummyfs", .mount = dummyfs_mount, .kill_sb = dummyfs_kill_sb, .fs_flags = FS_REQUIRES_DEV }; register_filesystem(&dummyfs_type)

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Fragments: lookup “implement ls”

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Fragment read/write

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User Space tools mkfs Initialize the device to be used by FS. Write initial FS state fsdb Development tool reading structures from raw device Understand on disk structure fsck Try to recover inconsistent state of FS (due to crash/corruption).

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Fragment mkfs

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Other resources: J.Lions: "A commentary on the sixth edition UNIX Operating System” V6 sources: S.R. Kleiman (86): “Vnodes: An Architecture for Multiple File System Types in Sun UNIX” McKusick (84): “A Fast File System for UNIX.” Steve D. Pate: "UNIX Filesystems: Evolution, Design and Implementation” github.com/gotoco/dummyfs