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virtual file system wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 implementations 2 single file virtual file systems toggle single file virtual file systems subsection 2 1 implementation of single file virtual filesystems 2 1 1 pctask 2 1 2 winuae 3 see also 4 notes 5 references 6 external links toggle the table of contents virtual file system 15 languages català čeština deutsch español فارسی français italiano 日本語 한국어 norsk bokmål polski português русский українська 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia abstract layer on top of a more concrete file system this article includes a list of general references but lacks sufficient corresponding inline citations please help improve this article by introducing more precise citations october 2009 learn how and when to remove this message operating systems common features process management interrupts memory management file system device drivers networking security input output v t e a virtual file system vfs or virtual filesystem switch is an abstract layer on top of a more concrete file system the purpose of a vfs is to allow client applications to access different types of concrete file systems in a uniform way a vfs can for example be used to access local and network storage devices transparently without the client application noticing the difference it can be used to bridge the differences in windows classic mac os macos and unix filesystems so that applications can access files on local file systems of those types without having to know what type of file system they are accessing a vfs specifies an interface or a contract between the kernel and a concrete file system therefore it is easy to add support for new file system types to the kernel simply by fulfilling the contract the terms of the contract might change incompatibly from release to release which would require that concrete file system support be recompiled and possibly modified before recompilation to allow it to work with a new release of the operating system or the supplier of the operating system might make only backward compatible changes to the contract so that concrete file system support built for a given release of the operating system would work with future versions of the operating system implementations edit the position of the vfs layer within various parts of the linux kernel s storage stack 1 one of the first virtual file system mechanisms on unix like systems was introduced by sun microsystems in sunos 2 0 in 1985 2 it allowed unix system calls to access local ufs file systems and remote nfs file systems transparently for this reason unix vendors who licensed the nfs code from sun often copied the design of sun s vfs other file systems could be plugged into it also there was an implementation of the ms dos fat file system developed at sun that plugged into the sunos vfs although it was not shipped as a product until sunos 4 1 the sunos implementation was the basis of the vfs mechanism in system v release 4 john heidemann developed a stacking vfs under sunos 4 0 for the experimental ficus file system this design provided for code reuse among file system types with differing but similar semantics e g an encrypting file system could reuse all of the naming and storage management code of a non encrypting file system heidemann adapted this work for use in 4 4bsd as a part of his thesis research descendants of this code underpin the file system implementations in modern bsd derivatives including macos other unix virtual file systems include the file system switch in system v release 3 the generic file system in ultrix and the vfs in linux in os 2 and microsoft windows the virtual file system mechanism is called the installable file system the filesystem in userspace fuse mechanism allows userland code to plug into the virtual file system mechanism in linux netbsd freebsd opensolaris and macos in microsoft windows virtual filesystems can also be implemented through userland shell namespace extensions however they do not support the lowest level file system access application programming interfaces in windows so not all applications will be able to access file systems that are implemented as namespace extensions kio and gvfs gio provide similar mechanisms in the kde and gnome desktop environments respectively with similar limitations although they can be made to use fuse techniques and therefore integrate smoothly into the system single file virtual file systems edit sometimes virtual file system refers to a file or a group of files not necessarily inside a concrete file system that acts as a manageable container which should provide the functionality of a concrete file system through the usage of software examples of such containers are cbfs connect from callback technologies or a single file virtual file system in an emulator like pctask or so called winuae oracle s virtualbox microsoft s virtual pc vmware the primary benefit for this type of file system is that it is centralized and easy to remove a single file virtual file system may include all the basic features expected of any file system virtual or otherwise but access to the internal structure of these file systems is often limited to programs specifically written to make use of the single file virtual file system instead of implementation through a driver allowing universal access another major drawback is that performance is relatively low when compared to other virtual file systems low performance is mostly due to the cost of shuffling virtual files when data is written or deleted from the virtual file system implementation of single file virtual filesystems edit direct examples of single file virtual file systems include emulators such as pctask and winuae which encapsulate not only the filesystem data but also emulated disk layout this makes it easy to treat an os installation like any other piece of software transferring it with removable media or over the network pctask edit the amiga emulator pctask emulated an intel pc 8088 based machine clocked at 4 77 mhz and later an 80486 sx clocked at 25 mhz users of pctask could create a file of large size on the amiga filesystem and this file would be virtually accessed from the emulator as if it were a real pc hard disk the file could be formatted with the fat16 filesystem to store normal ms dos or windows files 1 2 winuae edit the uae for windows winuae allows for large single files on windows to be treated as amiga file systems in winuae this file is called a hardfile 3 uae could also treat a directory on the host filesystem windows linux macos amigaos as an amiga filesystem 4 see also edit 9p protocol a distributed file system protocol that maps directly to the vfs layer of plan 9 making all file system access network transparent synthetic file system a hierarchical interface to non file objects that appear as if they were regular files in the tree of a disk based file system notes edit emulation on amiga comparison between pcx and pctask amiga pc emulators see also this article explaining how it works pctask help about winuae see hardfile section help about winuae see add directory section references edit werner fischer georg schönberger 2015 06 01 linux storage stack diagram thomas krenn ag retrieved 2015 06 08 kleiman steve r june 1986 vnodes an architecture for multiple file system types in sun unix pdf usenix summer 86 238 247 archived from the original pdf on 2014 06 29 retrieved 31 december 2016 linux kernel s virtual file system archived 2005 03 05 at the wayback machine rodriguez r m koehler r hyde june 1986 the generic file system proceedings of the usenix summer technical conference atlanta georgia usenix association pp 260 269 karels m m k mckusick september 1986 towards a compatible file system interface proceedings of the european unix users group meeting manchester england euug pp 481 496 heidemann john 1995 stackable design of file systems technical report ucla csd 950032 the linux vfs chapter 4 of linux file systems by moshe bar mcgraw hill 2001 isbn 0 07 212955 7 chapter 12 of understanding the linux kernel by daniel p bovet marco cesati o reilly media 2005 isbn 0 596 00565 2 the linux vfs model naming structure external links edit anatomy of the linux virtual file system switch v t e storage virtualization block level storage disk aggregation comparison distributed file systems file virtualization logical disk raid software defined storage virtual disk virtual file system v t e file systems comparison of file systems distributed unix filesystem disk and non rotating adfs advfs amiga ffs amiga ofs apfs athfs bcachefs bfs be file system boot file system byte file system z vm btrfs cvfs dfs efs encrypting file system extent file system episode ext ext2 ext3 ext4 fat exfat files 11 fossil gpfs hammer hammer2 hfs classic mac os hfs mvs hfs hpfs htfs jfs lfs mfs macintosh file system tivo media file system minix netware file system next3 nilfs nilfs2 nss ntfs onefs openzfs pfs qfs qnx4fs refs reiserfs reiser4 reliance reliance nitro rfs sfs shared file system vm smart file system snfs soup apple tux3 ubifs ufs ufs2 soft updates wapbl vxfs wafl xiafs xfs xsan zfs z os zfs sun optical disc hsf iso 9660 iso 13490 udf flash memory and ssd apfs fat exfat tfat erofs f2fs jfs nvfs host side wear leveling chfs jffs jffs2 logfs nilfs nilfs2 yaffs ubifs distributed parallel beegfs ceph gfs2 google file system ocfs2 orangefs pvfs qfs xsan more nas 9p afs openafs afp coda dfs google file system gpfs lustre ncp nfs pohmelfs hadoop smb cifs sshfs more specialized aufs axfs boot file system compact disc file system cramfs davfs2 erofs ftpfs fuse lnfs ltfs nova mvfs squashfs umsdos overlayfs unionfs pseudo configfs devfs debugfs kernfs procfs specfs sysfs tmpfs winfs encrypted ecryptfs encfs efs rubberhose sshfs zfs types clustered global grid self certifying flash journaling log structured object record oriented semantic steganographic synthetic versioning features case preservation copy on write data deduplication data scrubbing execute in place extent file attribute extended file attributes file change log fork inode links hard symbolic access control access control list filesystem level encryption permissions modes sticky bit interfaces file manager file system api installable file system virtual file system lists cryptographic default log structured layouts master boot record guid partition table apple partition map v t e operating systems general comparison forensic engineering history list timeline usage share user features comparison variants disk operating system distributed operating system embedded operating system hobbyist operating system just enough operating system mobile operating system network operating system object oriented operating system real time operating system supercomputer operating system kernel architectures exokernel hybrid microkernel monolithic multikernel vkernel rump kernel unikernel components device driver loadable kernel module user space and kernel space process management concepts computer multitasking cooperative preemptive context switch interrupt ipc process process control block real time thread time sharing scheduling algorithms fixed priority preemptive multilevel feedback queue round robin shortest job next memory management resource protection bus error general protection fault memory paging memory protection protection ring segmentation fault virtual memory storage access file systems boot loader defragmentation device file file attribute inode journal partition virtual file system virtual tape library supporting concepts api computer network hal live cd live usb shell cli user interface pxe retrieved from https en wikipedia org w index php title virtual_file_system oldid 1326295334 categories computer file systems virtualization hidden categories articles with short description short description is different from wikidata articles lacking in text citations from october 2009 all articles lacking in text citations webarchive template wayback links this page was last edited on 8 december 2025 at 04 40 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site 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