[[!meta copyright="Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] [[!tag stable_URL]] [[!toc]] # General Information A translator is simply a normal program acting as an object server and participating in the Hurd's distributed [[virtual_file_system]]. It is so-called because it typically exports a file system (although need not: cf. [[auth]], [[proc]] and [[pfinet]]) and thus translates object invocations into calls appropriate for the backing store (e.g., ext2 file system, nfs server, etc.). Another way of putting it is that it translates from one representation of a data structure into another representation, for example from the on-disk [[ext2|ext2fs]] data layout to a traditional file system hierarchy, or from a XML file to a virtual hierarchical manifestation. This translation can be a bidirectional process, but it need not be. A translator is usually registered with a specific file system node by using the [[`settrans`|settrans]] command. Translators do not require any special privilege to run. The privilege they require is simply that to access the indiviudal resources they use. This is primarily the [[backing_store]] and the node they attach to. Typically, a translator can only be attached to a node by the node's owner. On [[Unix]] this is not possible because file systems and the virtual file system are implemented in the kernel and thus have absolute access to the machine. As the protocols do not require any special privilege to implement, this is not an issue on the Hurd. In Mach parlance, a *translator* is what they name a *server*: a process that participates in [[RPC]] interactions. In the Hurd, a translator is a server that is additionally attached to a filesystem node. Thus, it is quite common, even in the Hurd context, to speak about *server*s if you're stressing the RPC part, and on the other hand about *translator*s if you're stressing the filesystem part: a translator implements the [[interface/fs]] and [[interface/io]] interfaces. For example: *the [[pfinet]] server implements the socket API calls (which are mapped by [[glibc]] to equivalent RPC calls)*, compared to *a [[libdiskfs]]-based translator implements a filesystem, based on a backing store*. As a translator is not different from any other user-space application, it can be written in any programming language. The practicable constraint is that an interface suitable for doing [[RPC]]s should exist, which currently only exists for C ([[microkernel/mach/MIG]]). For Lisp, Perl, [[user/jkoenig/Java]] there so far are only experimental and incomplete implementations. To learn how to write a translator, read the code! It is well documented, in particular, the header files. The [[Hurd_Hacking_Guide]] also has a tutorial. Also there is an [[writing/example]] about how to write a simple translator. See some [[examples]] about how to use translators. There is a [[documentation/translator_primer]]. Marcus Brinkmann has written a document about [[documentation/translators]]. Here are some [[hints_about_debugging_translators|debugging/translator]] available. Read about translator [[short-circuiting]]. The [[concept|concepts]] of translators creates its own problems, too: [[open_issues/translators_set_up_by_untrusted_users]], and [[open_issues/trust_the_behavior_of_translators]]. # Existing Translators * [[hello]] * [[auth]] * [[devnode]] * [[exec]] * [[ifsock]] * [[password]] * [[proc]] * [[procfs]] * [[pfinet]] * [[proxy-defpager]] * [[lwip]] * [[eth-filter]] * [[eth-multiplexer]] * [[pflocal]] * [[hostmux]] * [[startup]] * [[storeio]] * [[streamio]] * [[ext2fs]] * [[fatfs]] * [[ftpfs]] * [[magic]] * [[mtab]] * [[pci-arbiter]] * [[remap]] * [[unionfs]] * [[nfs]] * [[symlink]] * [[fakeroot]] * [[firmlink]] * [[fifo]] * [[term]] * [[checkperms]] * [[usermux]] * ... # Translators Being Under Development * [[random]] * [[cvsfs]] * [[tmpfs]] * [[procfs]] * [[nsmux]] * [[netio]] * [[socketio]] * [[tarfs]] * [[gopherfs]] * [[smbfs]] * ... # Translators (only) in Hurdextras *These Translators are available in the [hurdextras repository](http://savannah.nongnu.org/cvs/?group=hurdextras) but not yet described on this website. They are in varying stages of Development.* * [jfs](http://www.nongnu.org/hurdextras/#jfs) * [[httpfs]] * [memfs](http://www.nongnu.org/hurdextras/#memfs) * [notice](http://www.nongnu.org/hurdextras/#notice) * [pith](http://www.nongnu.org/hurdextras/#pith) * [pptop](http://www.nongnu.org/hurdextras/#pptop) * [run](http://www.nongnu.org/hurdextras/#run) * [[xmlfs]] * [[mboxfs]] Some of the above could be moved from hurdextras to [[source_repositories/incubator]], see the [[status page|open_issues/hurdextras]]. # Translator Wishlists * [[open_issues/network_file_system_by_just_forwarding_RPCs]] * [[libguestfs]] * [[devfs]] * [[emailfs]] -- email as a filesystem * [[general wishlist of stuff not listed above|wishlist]] # Internally ## `*_demuxer` Functions * IRC, unknown channel, unknown date what is a main idea of _demuxer functions in translators? jim-crow: Think of a web server. jim-crow: A typical web server must process many different requests. jim-crow: There are different types of requests. jim-crow: For instance, static pages and dynamically gnereated content. the static pages are processed by one function and the dynamic pages by another the thing that makes the decision which of these functions to pass the request to is the demuxer. neal: ok, I see but what is actually it doing in trivfs_demuxer? it looks at the message id and calls the right server stub for example it calls trivfs_io_server function, but I can't find its implementation that's my main question :-) look at the files mig generates neal: ok, thanks neal: is this functions where actually stubs are called? I think so. # Bounties There is a [[!FF_project 280]][[!tag bounty]] on some translator improvement tasks.