ExtensibleFileSystems - File System Extensibility and Non-...

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Unformatted text preview: File System Extensibility and Non- Disk File Systems Andy Wang COP 5611 Advanced Operating Systems Outline File system extensibility Non-disk file systems File System Extensibility Any existing file system can be improved No file system is perfect for all purposes So the OS should make multiple file systems available And should allow for future improvements to file systems Approaches to File System Extensibility Modify an existing file system Virtual file systems Layered and stackable file system layers Modifying Existing File Systems Make the changes you want to an already operating file system + Reuses code But changes everyones file system Requires access to source code Hard to distribute Virtual File Systems Permit a single OS installation to run multiple file systems Using the same high-level interface to each OS keeps track of which files are instantiated by which file system Introduced by Sun / A 4.2 BSD File System / B 4.2 BSD File System NFS File System Goals of Virtual File Systems Split FS implementation-dependent and -independent functionality Support semantics of important existing file systems Usable by both clients and servers of remote file systems Atomicity of operation Good performance, re-entrant, no centralized resources, OO approach Basic VFS Architecture Split the existing common Unix file system architecture Normal user file-related system calls above the split File system dependent implementation details below I_nodes fall below open() and read() calls above VFS Architecture Block Diagram System Calls System Calls V_node Layer V_node Layer PC File System PC File System 4.2 BSD File System 4.2 BSD File System NFS NFS Floppy Disk Floppy Disk Hard Disk Hard Disk Network Network Virtual File Systems Each VFS is linked into an OS- maintained list of VFSs First in list is the root VFS Each VFS has a pointer to its data Which describes how to find its files Generic operations used to access VFSs V_nodes The per-file data structure made available to applications Has both public and private data areas Public area is static or maintained only at VFS level No locking done by the v_node layer rootvfs vfs_next vfs_vnodecovered vfs_data BSD vfs 4.2 BSD File System NFS mount mount BSD rootvfs vfs_next vfs_vnodecovered vfs_data BSD vfs 4.2 BSD File System NFS mount v_vfsp v_vfsmountedhere v_data v_node / i_node / create root / rootvfs vfs_next vfs_vnodecovered vfs_data BSD vfs 4.2 BSD File System NFS mount v_vfsp v_vfsmountedhere v_data v_node / i_node / v_vfsp v_vfsmountedhere v_data v_node A i_node A create dir A rootvfs vfs_next vfs_vnodecovered vfs_data BSD vfs 4.2 BSD File System NFS mount v_vfsp v_vfsmountedhere v_data v_node / i_node / v_vfsp v_vfsmountedhere v_data v_node A i_node A vfs_next vfs_vnodecovered vfs_data NFS vfs mntinfo mount NFS rootvfs...
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This note was uploaded on 02/15/2012 for the course COP 4600 taught by Professor Montagne during the Fall '08 term at University of Central Florida.

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ExtensibleFileSystems - File System Extensibility and Non-...

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