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+[[!meta copyright="Copyright © 2008, 2009, 2010, 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 open_issue_gnumach open_issue_hurd open_issue_viengoos]]
+
+[[microkernel/Mach]] interfaces do not allow for proper resource accounting,
+when a server allocates resources on behalf of a client.
+
+Mach can't do a good job at resource management, as it doesn't have enough
+information how resources are used: which data is important and which is
+discardable, for example.
+
+These issues are what Neal Walfield is working on with his new kernel
+[[microkernel/viengoos]].
+
+
+# Kernel
+
+Inside the [[kernel]], there is commonly a need to allocate resources according
+to externally induced demand, dynamically.  For example, for memory-management
+data structures (page tables), process table entries, thread control blocks,
+[[capability]] tables, incoming network packages, blocks that are read in from
+disk, the keyboard type-ahead buffer for a in-kernel keyboard driver.  Some of
+these are due to actions driven by user-space requests, others are due to
+actions internal to the the kernel itself.  Some of these buffers can be sized
+statically (keyboard type-ahead buffer), and are thus unproblematic.  Others
+are not, and should thus be attributed to their user space entities.  In the
+latter (ideal) case, all resources -- that is, including those needed inside
+the kernel -- that a user space task needs for execution are provided by itself
+(and, in turn, provided by its parent / principal), and the kernel itself does
+not need to allocate any resources dynamically out of an its own memory pool.
+This avoids issues like [[microkernel/Mach]]'s [[zalloc_panics]] upon user
+space processes allocating too many [[microkernel/mach/port]]s, for example.
+
+[[!toggleable id=fof_plos09 text="""[[!template id=note
+text="*[[fof\_plos09|microkernel/barrelfish]]*:
+{{$microkernel/barrelfish#fof_plos09}}"]]"""]]
+
+[[!toggleable id=sel4 text="""[[!template id=note
+text="[[*sel4*|microkernel/l4]]: {{$microkernel/l4#sel4}}"]]"""]]
+
+In [[!toggle id=fof_plos09 text="[fof\_plos09]"]], the authors describe in
+section 3 how they model their [[capability]] system according to [[!toggle
+id=sel4 text="[sel4]"]] using a *retype* operation that *takes an existing
+capability and produces one or more derived capabilities [...] used to create
+new kernel-level memory objects (such as page tables or execution contexts)
+from capabilities to raw regions of RAM*.
+
+This is, of course, non-trivial to implement, and also requires changing the
+[[RPC]] interfaces, for example, but it is a valid approach, a research topic.
+
+([[!taglink open_issue_documentation]]: compare this to Linux [`vmsplice`'s
+SPLICE_F_GIFT
+flag](http://www.kernel.org/doc/man-pages/online/pages/man2/vmsplice.2.html#DESCRIPTION).)
+
+
+## IRC, freenode, #hurd, 2011-07-31
+
+    < braunr> one of the biggest problems on the hurd is that, when a client
+      makes a call, kernel (and other) resources are allocated on behalf of the
+      server performaing the requested action
+    < braunr> performing*
+    < braunr> this makes implementing scheduling and limits difficult
+    < CTKArcher> And could changing the kernel change anything to that ?
+    < braunr> yes but you'd probably need to change its interface as well
+    < braunr> iirc, the critique describes resource containers
+    < braunr> but no work has been done on the current hurd (hence the hurdng
+      attempts)
+
+
+## IRC, freenode, #hurd, 2013-08-13
+
+In context of <https://teythoon.cryptobitch.de/posts/my-worst-week-yet/>.
+
+    <braunr> teythoon: actually, thread migration isn't required for resource
+      accounting
+
+[[Mach_migrating_threads]].
+
+    <teythoon> braunr: but it solves it for free, doesn't it?
+    <braunr> teythoon: no
+    <braunr> it's really more complicated than that
+
+
+# Further Examples
+
+  * [[hurd/critique]]
+
+  * [[IO_accounting]]
+
+  * [[translators_set_up_by_untrusted_users]], and [[pagers]]
+
+  * [[configure_max_command_line_length]]
+
+
+## [[hurd/translator/exec]] server
+
+### IRC, freenode, #hurd, 2013-08-05
+
+    <teythoon> unzipping stuff in the exec server enables a dos on filesystem
+      translators
+    <teythoon> https://teythoon.cryptobitch.de/gsoc/heap/hello-1g.bz2 is
+      /hurd/hello padded with a gig of zeros, compressed with bzip2
+    <teythoon> if set as an passive translator, it stalls other requests to the
+      filesystem, at least it does if ext2fs is used
+    <braunr> teythoon: ?
+    <braunr> teythoon: what's the dos here ?
+    <teythoon> I can prevent you from doing anything with the root filesystem
+    <teythoon> I'm kind of surprised myself, maybe a lock is held during the
+      exec of the translator?
+    <teythoon> the filesystem the hello-1g.bz2 translator is bound to is
+      affected
+    <braunr> teythoon: i don't understand
+    <braunr> have you tried starting something from another file system ?
+    <braunr> the lock may simply be in the exec server itself
+    <teythoon> no, starting other things works fine
+    <teythoon> but on the other hand, a find / is stalled
+    <braunr> :/
+    <braunr> *sigh*
+    <teythoon> don't worry
+    <teythoon> there is a solution :p
+    <braunr> :)
+    <teythoon> and it only requires deleting code