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authorThomas Schwinge <tschwinge@gnu.org>2009-03-05 19:20:56 +0100
committerThomas Schwinge <tschwinge@gnu.org>2009-03-05 19:20:56 +0100
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+[[meta copyright="Copyright © 2008, 2009 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]]."]]"""]]
+
+[[meta title="Fix tmpfs"]]
+
+In some situations it is desirable to have a file system that is not backed by
+actual disk storage, but only by anonymous memory, i.e. lives in the RAM (and
+possibly swap space).
+
+A simplistic way to implement such a memory filesystem is literally creating a
+ramdisk, i.e. simply allocating a big chunck of RAM (called a memory store in
+Hurd terminology), and create a normal filesystem like ext2 on that. However,
+this is not very efficient, and not very convenient either (the filesystem
+needs to be recreated each time the ramdisk is invoked). A nicer solution is
+having a real [[hurd/translator/tmpfs]], which creates all filesystem
+structures directly in RAM, allocating memory on demand.
+
+The Hurd has had such a tmpfs for a long time. However, the existing
+implementation doesn't work anymore -- it got broken by changes in other parts
+of the Hurd design.
+
+There are several issues. The most serious known problem seems to be that for
+technical reasons it receives [[microkernel/mach/RPC]]s from two different
+sources on one [[microkernel/mach/port]], and gets mixed up with them. Fixing
+this is non-trivial, and requires a good understanding of the involved
+mechanisms.
+
+The goal of this project to get a fully working, full featured tmpfs
+implementation. It requires digging into some parts of the Hurd, incuding the
+[[pager_interface|hurd/libpager]] and [[hurd/translator]] programming. This
+task probably doesn't require any design work, only good debugging skills.
+
+Possible mentors: ?
+
+Exercise: Take a go at one of the existing issues in tmpfs. You may not be able
+to finish this in the limited amount of time, but you should at least be able
+to do a detailed analysis of the problem.