path: root/open_issues/virtualization/fakeroot.mdwn

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[[!tag open_issue_hurd]]


# IRC, freenode, #hurd, 2013-02-26

    <youpi> btw, about fakeroot-hurd
    <youpi> the remaining issue I see is with argv[0] (yes, again...)


## IRC, freenode, #hurd, 2013-04-03

    <youpi> btw, I believe our fakeroot-hurd is close to working actually
    <youpi> it's just a argv[0] issue supposed to be fixed by exec_file_name
      but apparently not fixed in that case, for some reason

[[glibc#execve_relative_paths]].


## IRC, freenode, #hurd, 2013-08-26

    < teythoon> also I looked into the fakeroot issue, aiui the problem is that
      scripts are not handled correctly, right?
    < teythoon> the exec server fails to locate the scripts file name, and so
      it hands the file_t to the interpreter process and passes /dev/fds/3 as
      script name
    < teythoon> afaics that breaks e.g. python
    < youpi> yes
    < youpi> pinotree's exec_file_name is supposed to fix that, but for some
      reason it doesn't work here

[[glibc#execve_relative_paths]].

    < pinotree> it was pochu's, not mine
    < youpi> ah, right
    < teythoon> ah I see, I was wondering about that
    < pochu> it was working for a long time, wasn't it?
    < pochu> and only stopped working recently
    < youpi> did it completely stop?
    < youpi> I have indeed seen odd issues
    < youpi> I haven't actually  checked whether it has completely stopped
      working
    < youpi> probably worth looking there first
    < pinotree> gtk+3.0 fails, but other stuff like glib2.0 and gtester-using
      stuff works
    < teythoon> huh? I created tests like "#!/bin/sh\necho $0" and that says
      /dev/fd..., and a python script doing the same doesn't even run, so how
      can it work for a package build?
    < youpi> it works for me in plain bash
    < youpi> #!/bin/sh
    < youpi> echo $0
    < youpi> € $PWD/test.sh
    < youpi> /home/samy/test.sh
    < teythoon> it does !?
    < youpi> yes
    < youpi> not in fakeroot-hurd however, as we said
    < teythoon> well, obviously it works when not being run under
      fakeroot-hurd, yes
    < youpi> ok, so we weren't talking about the same thing
    < youpi> a mere shell script doesn't work in fakeroot-hurd indeed
    < youpi> that's why we still use fakeroot-sysv
    < teythoon> right
    < youpi> err, -tcp


## IRC, freenode, #hurd, 2013-11-18

    <teythoon> I believe I figured out the argv[0] issue with fakeroot-hurd
    <teythoon> but I'm not sure how to fix this
    <teythoon> first of all, Emilios file_exec_file_name patch set works fine

[[glibc#execve_relative_paths]].

    <teythoon> but not with fakeroot
    <teythoon>
      http://git.sceen.net/hurd/hurd.git/blob/HEAD:/exec/hashexec.c#l300
    <teythoon> check_hashexec tries to locate the script file using a heuristic
    <teythoon> Emilios patch improves the situation with just providing this
      information
    <teythoon> but then, the identity port of the "discovered" file is compared
      with the id port of the script file
    <teythoon> to verify if the heuristic found the right file
    <teythoon> but when using fakeroot-hurd, /hurd/fakeroot proxies all
      requests
    <teythoon> but the exec server is outside of the /hurd/fakeroot
      environment, so it gets the id port from the real filesystem
    <teythoon> we could skip that test if the script name is explicitly
      provided though
    <teythoon> that test was meant to see whether a search through $PATH turned
      up the right file
    <braunr> teythoon: nice
    <teythoon> braunr: thanks :)
    <teythoon> unfortunately, dpkg-buildpackaging hurd with it still fails for
      some reason
    <teythoon> but it is faster than fakeroot-tcp :)
    <braunr> even chown ?
    <braunr> or chmod ?
    <teythoon> dunno in detail, but the whole build is faster
    <braunr> if you can try it, i'm interested
    <braunr> because chown/chmod is also slow on linux with fakeroot-tcp
    <teythoon> i can try...
    <braunr> so it's probably not a hurd bug
    <teythoon> braunr: yes, it really is
    <braunr> no i mean
    <braunr> chown/chmod being slow with fakeroot-tcp is probably not a hurd
      bug
    <braunr> but a fakeroot-tcp bug
    <teythoon> chowning all files in /usr/bin takes 5.930s with fakeroot-hurd
      (6.09 with startup overhead) vs 26.42s (26.59s) with fakeroot-tcp
    <braunr> but try it on linux (fakeroot-tcp i mean)
    <braunr> although you may want to do it on something you don't care much
      about :p)


## IRC, freenode, #hurd, 2013-12-03

    * teythoon is gonna hunt a fakeroot bug ...
    <teythoon> % fakeroot-hurd /bin/sh -c ":> /tmp/some_file"
    <teythoon> /bin/sh: 1: cannot create /tmp/some_file: Is a directory
    <braunr> ah fakeroot-hurd
    <teythoon> prevents installing stuff with /bin/install
    <teythoon> sure fakeroot-hurd, why would i work on the slow one ?
    <braunr> i don't know
    <braunr> because it makes chmod/chown/maybe others horrenddously slow
    <braunr> ?
    <teythoon> yes, fixing this involves fixing fakeroot-hurd
    <braunr> are you sure ?
    <braunr> i prefer repeating just in case: i saw that problem on linux as
      well
    <braunr> with fakeroot-sysv
    <teythoon> so ?
    <braunr> i'm almost certain it's a pure fakeroot bug, not a hurd bug
    <braunr> so
    <teythoon> even if this is fixed, it still has to pay the socket
      communication overhead
    <braunr> fixing fakeroot-hurd so that i can be used instead of fakeroot-tcp
      is a very good thing to do, obviously
    <braunr> it*
    <braunr> but it won't solve the chown/chmod speed
    <braunr> (or, probably won't)
    <teythoon> huh, why not ?
    <braunr> 15:53 < braunr> i'm almost certain it's a pure fakeroot bug, not a
      hurd bug
    <braunr> when i say it's slow, i should be more precise
    <braunr> it doesn't show up in top
    <teythoon> yes, but why would fakeroot-hurd suffer from the same issue ?
    <braunr> the cpu is almost idle
    <braunr> oh right, it's a completely different tool
    <braunr> my bad
    <braunr> right, right, the proper way to implement fakeroot actually :)
    <teythoon> yes
    <teythoon> this will bring near-native speed


## IRC, freenode, #hurd, 2013-12-05

    <teythoon> fakeroot-hurd just successfully built mig :)
    <teythoon> hangs in dh_gencontrol when building gnumach or hurd though
    <teythoon> i believe it hangs waiting for a lock
    <teythoon> lock like in file lock that is
    <teythoon> braunr: no more room for vm_map_find_entry in 80220a40
    <teythoon> 80220a40 <- is that a task ?
    <braunr> or a vm_map, not sure
    <braunr> probably a vm_map


## IRC, freenode, #hurd, 2013-12-06

    <teythoon> well, aren't threads a source of endless entertainment ... ?
    <teythoon> well, I found three more bugs in fakeroot-hurd
    <teythoon> one of them requires fixing the locking used in fakeroot
    <braunr> ouch
    <teythoon> the current code does some lock cycling to aquire a lock out of
      order
    <braunr> cycling ?
    <teythoon> in the netfs_node_norefs function
    <teythoon> release and reaquire
    <braunr> i see
    <teythoon> which imho should be better solved with a weak reference
    <teythoon> working on it, it no longer deadlocks but i broke something else
      ...
    <teythoon> endless fun ;)
    <braunr> such things could have been done right in the beginning
    <braunr> ...
    <teythoon> yes, I wonder
    <teythoon> libports has weak references
    <teythoon> but pflocal is the only user
    <braunr> hm
    <teythoon> none of the lib*fs support that
    <braunr> didn't i add one in libdiskfs too ?
    <braunr> anyway, irrelevant
    <braunr> weak references are a nice feature
    <braunr> teythoon: i don't see the cycling you mentioned
    <braunr> only netfs_node_refcnt_lock being dropped temporarily
    <teythoon> yep, that one
    <teythoon> line 145
    <teythoon> note that due to another bug this code is currently never run
    <braunr> how surprising ..
    <braunr> the note about some leak actually gave a hint about that
    <teythoon> yeah, that leak
    <teythoon> I think i'm actually very close
    <teythoon> it's just so frustrating, i thought i got it last night
    <braunr> good luck then
    <teythoon> thanks :)


## IRC, freenode, #hurd, 2013-12-09

    <teythoon> sweet, i fixed fakeroot-hurd :)
    <braunr>  /clap
    <braunr> what was the problem ?
    <teythoon> lots
    <braunr> i see
    <teythoon> it's amazing it actually run as well as it did
    <braunr> mess strikes again
    <braunr> i hate messy code ..
    * teythoon is building half a hurd package using this ... stay tuned ;)
    <azeem> teythoon: is this going to make building faster as well?
    <teythoon> most likely, yes
    <teythoon> fakeroot-tcp is known to be slow, even on linux
    <braunr> teythoon: are you sure about the transparent retry patch ?
    <teythoon> pretty sure, why ?
    <braunr> it's about a more general issue that we didn't fix yet
    <braunr> our last discussions about it lead us to agree that clients should
      check the identity of a server before interacting with it
    <teythoon> braunr: i don't understand, what's the problem here ?
    <braunr> teythoon: fakeroot does the lookup itself, doesn't it ?
    <teythoon> yes
    <braunr> teythoon: but was that also the case before your patch ?
    <teythoon> braunr: yes
    <braunr> teythoon: then ok
    <braunr> teythoon: i guess fakeroot handles requests only for a specific
      set of calls right ?
    <braunr> and for others, requests are directly relayed
    <teythoon> braunr: yes
    <braunr> and that still is the case, right ?
    <teythoon> yes
    <braunr> ok
    <braunr> looks right since it only affects lookups
    <braunr> ok then
    <teythoon> well, fakeroot-hurd built half a hurd package in less than 70
      minutes
    <teythoon> a new record for my box
    <braunr> compared to how much before ?
    <braunr> (and why half of it ?)
    <teythoon> unfortunately it hung after signing the packages... some perl
      process with a /usr/bin/tee child
    <teythoon> killing tee made it succeed though
    <teythoon> braunr: i don't build the udeb package
    <braunr> oh ok
    <teythoon> braunr: compared with ~75 with fakeroot-tcp and my demuxer
      rework, ~80 before
    <braunr> teythoon: nice


## IRC, freenode, #hurd, 2013-12-18

    <teythoon> there, i fixed the last fakeroot-hurd bug
    <teythoon> *whee* :)
    <teythoon> i thought so many times that i got the last fakeroot bug ...
    <teythoon> last as in it's in a good enough shape to compile the hurd
      package that is
    <teythoon> but now it is
    <braunr> :)
    <braunr> this will make glibc and others so much faster to build


## IRC, freenode, #hurd, 2013-12-19

    <braunr> teythoon_: hum, you should make the behaviour of fakeroot-hurd on
      the last client exiting optional
    <teythoon_> y?
    <teythoon_> fakeroot-tcp does the very same thing
    <braunr> fakeroot-hurd is different
    <braunr> it's part of the file system
    <teythoon_> yes
    <braunr> users may want it to stay around
    <braunr> and reuse it without checking it's actually there
    <teythoon_> but once the last client is gone, who is ever getting another
      port to it ?
    <teythoon_> no
    <teythoon_> that cannot happen
    <braunr> really ?
    <teythoon_> yes
    <braunr> i thought it was like remap
    <braunr> since remap is based on it
    <teythoon_> the same thing applies to remap
    <teythoon_> only settrans has the control port
    <braunr> hum
    <teythoon_> and uses it once to get a protid for the working dir of the
      initial process started inside the chrooted environment
    <braunr> you may not want to chroot inside
    <teythoon_> so ?
    <teythoon_> then, you get another protid
    <braunr> i'll make an example
    <braunr> i create a myroot directory implemented by fakeroot
    <braunr> populate it
    <braunr> leave and do something else,
    <braunr> i might want to return to it later
    <teythoon_> ah
    <teythoon_> ok, so you are not using settrans --chroot

[[hurd/settrans/discussion#chroot]].

    <braunr> or maybe i'm confusing the fakeroot translator and fakeroot-hurd
    <braunr> 10:48 < braunr> you may not want to chroot inside
    <braunr> yes
    <teythoon_> hm
    <teythoon_> ok, so the patch could be changed to check whether the last
      control port is gone too
    <braunr> i have no idea of any practical use, but i don't see a valid
      reason to make a translator go away just because it has no client
    <braunr> except for resource usage
    <braunr> and if it's installed as a passive translator
    <braunr> although that would make fakeroot loose its state
    <braunr> though remap state is on the command line so it would be fine for
      it
    <braunr> see what i mean ?
    <teythoon_> yes i do
    <braunr> fakeroot state could be saved in some db one day so it may apply,
      if anyone feels the need
    <teythoon_> so what about checking for control ports too ?
    <braunr> i'm not too familiar with those
    <braunr> who has the control port of a passive translator ? the parent ?
    <teythoon_> that should cover the use case you described
    <teythoon_> for the parent translator
    <teythoon_> for fsys_getroot requests it has to keep it around
    <teythoon_> and for more fsys stuff too
    <braunr> and if active ? settrans ? who just looses it ?
    <teythoon_> if settrans is used to start an active translator, the parent
      fs still gets a right to the control port
    <braunr> ok
    <braunr> i don't have a clear view of what this implies for fakeroot-hurd
    <braunr> we'd want fakeroot-hurd to clean all resources including the
      fakeroot translator on exit
    <teythoon_> for fakeroot-hurd (or any child translator) this means that a
      port from the control port class will still exists
    <teythoon_> so we do not exit
    <teythoon_> oh, you're speaking of fakeroot.sh ? the wrapper script ?
    <braunr> probably
    <braunr> for me, fakeroot-hurd is the command line too, similar to
      fakeroot-sysv and fakeroot-tcp
    <braunr> and fakeroot is the translator
    <teythoon_> yes, agreed
    <teythoon_> fakeroot-hurd could use settrans --force --chroot ... to force
      fakeroot to exit if the main chrooted process dies
    <teythoon_> but that'd kill anything that outlives that process
    <teythoon_> that might be legitimate, say a process daemonized
    <teythoon_> so detecting that noone uses fakeroot is the much cleaner
      solution
    <braunr> ok
    <teythoon_> also, that's what fakeroot-tcp does
    <braunr> which is why i suggested an option for that
    <teythoon_> why add an option if we can do the right thing without
      troubling the user ?
    <braunr> ah, if we can, good
    <teythoon_> i think we can
    <teythoon_> I'll rework the patch, thanks for the hint
    <braunr> so
    <braunr> just to be clear
    <braunr> the way you intend it to work is
    <braunr> wait for all clients and the control port to drop before shutting
      down
    <braunr> the control port is dropped when dettaching the translator, right
      ?
    <teythoon_> yes
    <braunr> but hm
    <braunr> what if clients spawn other processes ?
    <braunr> they won't find the translator any more
    <teythoon_> then, that client get's a port to fakeroot at least for it's
      working dir
    <teythoon_> so another protid is created
    <braunr> ah yes, it's usually choorted for such uses
    <braunr> chrooted
    <teythoon_> so fakeroot will stick around
    <braunr> but clients, even from fakeroot, might simply use absolute paths
    <teythoon_> so ?
    <braunr> in which case they won't find fakeroot
    <teythoon_> it will hit fakeroots dir_lookup
    <teythoon_> sure
    <braunr> how so ?
    <teythoon_> if the path is absolute, it will trigger a magic retry of some
      kind
    <teythoon_> so the client uses it's root dir port
    <braunr> i thought the lookup would be done straight from the root fs port
      ..
    <teythoon_> which points to fakeroot of course
    <braunr> ah, chrooted again
    <teythoon_> that's the whole point
    <braunr> so this implies clients are chrooted
    <teythoon_> they are
    <teythoon_> even if you do another chroot
    <braunr> what i mean is
    <teythoon_> that root port also points to a fakeroot port
    <braunr> if we detach the translator, and clients outside the chroot spawn
      processes, say shell scripts, they won't find the fakeroot tree
    <braunr> now, i wonder if we want to actually handle that
    <braunr> i'm just uncomfortable with a translator silently shutting down
      because it has no client
    <teythoon_> if fakeroot is detached, how are clients outside the chroot
      ever supposed to get a handle to files inside the fakerooted env ?
    <braunr> it makes sense for fakeroot, so the expected behaviours here aer
      conflicting
    <braunr> they had those before fakeroot being detached
    <teythoon_> then fakeroot wouldn't go away
    <braunr> right
    <braunr> unless there is a race but i don't think there is
    <teythoon_> there isn't
    <teythoon_> i call netfs_shutdown
    <braunr> clients get the rights before the parent has a chance to terminate
    <teythoon_> and only shutdown if it doesn't return ebusy
    <braunr> makes sense
    <braunr> ok go ahead :)
    <teythoon_> cool, thanks for the walk-through ;)
    <braunr> on the other hand ..
    <braunr> that's a complicated topic left unfinished by the original authors
    <teythoon_> one of many
    <braunr> having translators automatically go away when there is no client
      may be a good feature
    <braunr> but it only makes sense for passive translators
    <braunr> and this should be automated
    <braunr> the lib*fs libraries should be able to handle it
    <teythoon_> or, we could go for proper persistence instead
    <braunr> stay around if active, leave after a while when no more clients if
      passive
    <braunr> why ?
    <teythoon_> clean solution
    <braunr> persistence looks much more expensive to me
    <teythoon_> other benefits
    <braunr> i mean
    <braunr> persistence looks so expensive it doesn't make sense in a general
      purpose system
    <teythoon_> sure, we could make our *fs libs handle this smarter at a much
      lower cost
    <teythoon_> don't we get a handle to the underlying file ?
    <braunr> i think we do yes
    <teythoon_> if that's actually a file and not a directory, we could store
      data into it
    <braunr> many translators are read-only
    <teythoon_> so ?
    <braunr> well, when we can write, we can use passive translators instead
    <braunr> normally
    <teythoon_> yes
    <braunr> depends on the fs type actually but you're right, we could use
      regular files
    <braunr> or a special type of file, i don't know
    <antrik> braunr: BTW, I agree that active translators should only go away
      when no ports are open anymore, while passive ones can exit when control
      ports are still open but no protids
    <teythoon> antrik: you mean as a general rule ?
    <teythoon> that leaves the question how the translator distinguishes
      between having a passive translator record and not having one
    <antrik> I believe I already arrived at that conclusion in some design
      discussion, probaly regarding namespace-based translator selection
    <antrik> teythoon: yeah, as a general rule
    <teythoon> interesting
    <antrik> currently there are command line arguments controling timeouts,
      but they don't consider control ports IIRC
    <teythoon> i thought there are problems with shutting down translators in
      general
    <antrik> (also, command line arguments seem inconvenient to distinguish the
      passive vs. active case...)
    <teythoon> yeah, but we disregard the timeouts in the debian flavor of hurd
    <antrik> teythoon: err... no we don't. at least not last time I knew. are
      you confusing this with thread timeouts?
    <antrik> simple test: do ls -l on /dev, wait a few minutes, compare
    <teythoon> what do you expect will happen ?
    <antrik> the unused translators should go away
    <teythoon> no
    <antrik> that must be new then
    <teythoon> might be, yes
    <teythoon>
      http://darnassus.sceen.net/cgit/teythoon/packaging/hurd.git/blame/HEAD:/debian/patches/libports_stability.patch
    <braunr> antrik: debian currently disables both the global and thread
      timeouts in libports
    <braunr> my work on thread destruction consists in part in reenabling
      thread timeouts, and my binary packages do that well so far :)
    <antrik> braunr: any idea why the global timeouts were disabled?


## IRC, freenode, #hurd, 2013-12-20

    <braunr> antrik: not sure
    <braunr> but i suspect there could be races
    <braunr> if a message arrives while the server is going away, i'm not sure
      the client can determine this and retry transparently
    <antrik> good point... not sure how that is supposed to work exactly


## IRC, freenode, #hurd, 2013-12-31

    <braunr> btw, we should remove the libports_stability patch and directly
      change the upstream code
    <braunr> if you agree, i can force the global timeout to 0 (because we're
      still not sure what can go wrong when a translator goes away while a
      message is being delivered to it)
    <braunr> i didn't experience any slowdown with thread destruction however
    <braunr> so i'm tempted to set that to an actual reasonable timeout value
      of 30-300 seconds
    <teythoon> braunr: if you do, please introduce a macro for the default
      value so it can be changed easily
    <braunr> teythoon: yes
    <braunr> i don't understand why these are left as parameters tbh
    <teythoon> true
    <braunr> 30 seconds seems to be plenty enough


## IRC, freenode, #hurd, 2014-01-17

    <braunr> time to give fakeroot-hurd a shot
    <braunr> http://darnassus.sceen.net/~rbraun/darnassus_fakeroot_hurd_assert
    <teythoon> braunr: (wrt fakeroot-hurd) well in my book that shouldn't
      happen
    <teythoon> that's why i put the assertion there ;)
    <braunr> i assumed so :)
    <teythoon> then again, /me does not agree with "threads" as concurrency
      model >,<, and that feeling seems to be mutual :p
    <braunr> ?
    <teythoon> well, obviously, the threads do not agree with me wrt to that
      assertion
    <braunr> the threads ?
    <teythoon> well, fakeroot is a multithreaded server
    <braunr> teythoon: i'm not sure i get the point, are you saying you're not
      comfortable with threads ?
    <teythoon> that's exactly what i'm saying
    <braunr> ok
    <braunr> coroutines/functional i guess ?
    <teythoon> csp
    <teythoon> functional not so much


## IRC, freenode, #hurd, 2014-01-20

[[open_issues/libpthread]],
[[open_issues/libpthread/t/fix_have_kernel_resources]].

    <braunr> teythoon: it's perfectly possible that the bug i had with
      fakeroot-hurd have been caused by my own glibc thread related patches
    <braunr> has*
    <teythoon> ok
    <teythoon> *phew* :p
    <braunr> :)
    <teythoon> i wonder if youpi could reproduce his issue on his machine
    <braunr> what issue ?
    <braunr> i must have missed something
    <teythoon> some package failed
    <teythoon> but he didn't gave any details
    <teythoon> he wanted to try it on his vm first
    <braunr> ok


## IRC, freenode, #hurd, 2014-01-21

    <braunr> teythoon: i still get the same assertion failure with
      fakeroot-hurd
    <braunr> will take a look at that sometimes too
    <teythoon> braunr: hrm :/
    <braunr> teythoon: don't worry, i'm sure it's nothing big
    <braunr> in the mean time, there are updated hurd and glibc packages on my
      repository with fixed tls and thread destruction
    <teythoon> cool :)


## IRC, freenode, #hurd, 2014-01-23

    <braunr> teythoon: can you briefly explain this fake reference thing in
      fakeroot when you have some time please ?
    <teythoon> braunr: fakeroot creates ports to hand out to clients
    <teythoon> every port represents a node and references a real node
    <teythoon> fakeroot allows one to set attributes, e.g. file permissions on
      any node as if the client was root
    <teythoon> those faked attributes are stored in the node objects
    <braunr> let's focus on fake_reference please
    <teythoon> once some attribute is faked, that node has to be kept alive
    <teythoon> otherwise, that faked information is lost
    <teythoon> so if the last peropen object is closed and some information is
      faked, a fake reference is kept
    <teythoon> as indicated by a flag
    <braunr> hm
    <teythoon> in dir lookup, if a node is looked-up that has a fake reference,
      it is recycled, i.e. the flag cleared and the referecne count is not
      incremented
    <teythoon> so every time fakeroot_netfs_release_protid is called b/c, the
      node in question should not have the fake reference flag set
    <braunr> what's the relation between the number of hard links and this fake
      reference ?
    <teythoon> i don'
    <teythoon> i don't think fakeroot has a notion of 'hard links'
    <braunr> it does
    <braunr> the fake reference is added on nodes with a hard link count
      greater than 0
    <braunr> but i guess that just means the underlying node still exists
    <teythoon> ah yes
    <teythoon> right
    <teythoon> currently, if the real node is deleted, the fake node is still
      kept around
    <braunr> let's say it's ok for now
    <teythoon> that's what the comment is talking about, the one that indicates
      that garbage collection could help here
    <teythoon> yes
    <teythoon> properly fixing this is difficult
    <braunr> agreed
    <braunr> it would require something like inotify anyway
    <teythoon> b/c of the way file deletion works
    <braunr> let's just ignore the issue, that's not what i'm hunting
    <teythoon> agreed
    <braunr> the assertion i have is telling us that we're dropping a fake
      reference
    <braunr> are we certain this isn't possible ?
    <teythoon> that function is called if a client dereferences a port
    <teythoon> in order to have a port in the first place, it has to get it
      from a dir_lookup
    <teythoon> the dir lookup turns a fake reference into a real one
    <teythoon> so i'm certain of that (barring a race condition somewhere)
    <braunr> ok
    <braunr> netfs_S_dir_lookup grabs idport_ihash_lock (line 354) but doesn't
      release it if nn == NULL (lines 388-392)
    <teythoon> hm, my file numbers are slightly different o_O
    <braunr> i have printfs around
    <braunr> sorry :)
    <teythoon> ok
    <teythoon> new node unlocks it
    <teythoon> new_node
    <braunr> oh
    <braunr> how unintuitive ..
    <teythoon> yes, don't blame me ;) that's how it was
    <braunr> :)
    <braunr> worse, the description says "if successful" ..
    <braunr> ah no, the node lock
    <braunr> ok
    <teythoon> yes, badly worded description
    <braunr> i strongly doubt it's a race
    <teythoon> how do you trigger that assertion failure ?
    <braunr> dpkg-buildpackage -rfakeroot-hurd -uc -us
    <braunr> for the hurd package
    <braunr> very similar to one of your test cases i think
    <teythoon> umm :-/
    <braunr> one thing that i find confusing is that fake_reference seems to
      apply to nodes, whereas release_protid is about, well, protids
    <braunr> is there a 1:1 relationship ?
    <braunr> since there is a peropen in the protid, i assume not
    <braunr> it may be a race actually
    <braunr> np->references must be accessed with netfs_node_refcnt_lock locked
    <braunr> hm no, that's not it
    <teythoon> no, it's not a 1:1 relationship
    <teythoon> note that the lock idport_ihash_lock serializes most operations,
      despite it's name indicating that it's only for the hash table
    <teythoon> the "interesting" operations being dir_lookup and release_protid
    <braunr> yes
    <braunr> again, that's another issue
    <teythoon> why ? that's a pretty strong guarantee already
    <braunr> ah yes, i was referring to scalability
    <teythoon> sure
    <braunr> the assertion is triggered from ports_port_deref in
      ports_manage_port_operations_multithread
    <teythoon> but i found it hard to reason about fakeroot, there are multiple
      locks involved, two kinds of reference counting across different libs
    <braunr> yes
    <teythoon> yes, that's to be expected
    <braunr> teythoon: do we agree that the fake reference is reused by a
      protid ?
    <teythoon> braunr: yes
    <braunr> why is there a ref counter for the protid as well as the peropen
      then ? :/
    <teythoon> funny... i thought there was no refcnt for the peropen objects,
      but there is
    <teythoon> but for fakeroot-hurd that shouldn't matter, right ?
    <braunr> i don't know
    <teythoon> here, one protid object is associated with one peropen object
    <braunr> yes
    <teythoon> and the other way around, i.e. it's 1:1
    <teythoon> so the refcount for those should be identical
    <braunr> but i get a case where protid has a refcnt of 0 while the peropen
      has 2 ..
    <teythoon> umm, that doesn't sound right
    <braunr> teythoon: ok, it does look like a race on np->references
    <braunr> node references are protected by a global lock in lib*fs libs
    <teythoon> yes
    <braunr> you check it without holding it
    <braunr> which means another protid can be closed at the same time, setting
      the flag on the underlying node
    <braunr> i'll make a proper patch soon
    <teythoon> they cannot both hold the hash lock
    <braunr> hm
    <braunr> teythoon: actually, i don't see why that's relevant
    <braunr> one thread closes its protid, sets the fakeref flag
    <braunr> the other does the same, chokes on the assertion
    <braunr> serially
    <teythoon> i'm always a little fuzzy when exactly the references get
      decremented
    <teythoon> but shouldn't only the second thread set the fakeref flag ?
    <braunr> well, that's not what i see
    <braunr> i'll check what happens to this ref counter
    <teythoon> see how my release_protid function calls netfs_release_protid
      just after the out label
    <teythoon> *while holding the big hash lock
    <teythoon> so, any refcounting should happen while the lock is being held,
      no ?
    <braunr> perhaps
    <braunr> now, my logs show something new
    <braunr> a case where the protid being released was never printed before
    <braunr> i.e. not obtained from dir_lookup
    <braunr> or at least, not fakeroot dir_lookup
    <teythoon> huh, where did it came from then ?
    <braunr> no idea
    <teythoon> only dir_lookup hands out those
    <braunr> check_openmodes calls dir_lookup too
    <teythoon> yes, but that's not our dir_lookup
    <braunr> that's what i mean
    <braunr> it bypasses fakeroot's custom dir_lookup
    <braunr> but i guess the reference already exists at this point
    <teythoon> bypass ? i wouldn't call it that
    <braunr> you're right, wrong wording
    <teythoon> it accesses files on other translators
    <braunr> yes
    <braunr> the netnode is already present
    <teythoon> yes
    <braunr> could it be the root node ?
    <teythoon> i do not believe so
    <teythoon> the root node is always faked
    <teythoon> and is handed out to the first process in the fakeroot env for
      it's current directory port
    <teythoon> so you could try something that chdirs away to test that
      hypothesis
    <braunr> the assertion looks triggered by a chdir
    <teythoon> how do you know that ?
    <braunr> dh_auto_install: error: unable to chdir to build-deb
    <teythoon> ah
    <teythoon> well, or that is just the operation after fakeroot died and
      completely unrelated
    <braunr> maybe
    <teythoon> can you trigger this reliably ?
    <braunr> yes
    <braunr> i'm trying to write a shell script for that
    <teythoon> so for you, fakeroot-hurd never succeeded in building a hurd
      package ?
    <braunr> no
    <teythoon> on darnassus ?
    <braunr> yes
    <teythoon> b/c i stopped working on fakeroot-hurd when it was in a
      good-enough shape to build the hurd package
    <teythoon> >,<
    <teythoon> maybe my system is not fast enough to hit this race (if it turns
      out to be one)
    <braunr> some calls seems to decrease the refcount of the root node
    <braunr> call*
    <teythoon> have you confirmed that it's the root node ?
    <braunr> almost
    <braunr> i could say yes
    <braunr> teythoon: actually no, it's not ..
    <braunr> could be ..
    <braunr> teythoon: on what node does fakeroot-hurd install the fakeroot
      translator when used to build debian packages ?
    <braunr> hum
    <braunr> could it simply be that the check on np->references should be
      moved above the assertion ?
    <teythoon> braunr: it is not bound to any node, check settrans --chroot

[[hurd/settrans/discussion#chroot]].

    <braunr> oh right
    <braunr> teythoon: ok i mean
    <braunr> does it shadow / ?
    <braunr> looks very likely, otherwise the chroot wouldn't work
    <teythoon> i'm not sure what you mean by shadow
    <braunr> settrans --chroot cmd -- / /hurd/fakeroot ?
    <teythoon> but yes, for any process in the chroot-like env every real node
      is replaced, including /
    <braunr> makes sense
    <braunr> teythoon: moving the assertion seems to fix the issue
    <braunr> intuitively, it seems reasonable to assume the fakeref flag can
      only be set when there is only one reference, namely the fake reference
    <braunr> (well, the fake ref, recycled by the last open)
    <teythoon> no, i don't follow
    <teythoon> i'd still say, that if ...release_protid is called, then there
      is no way for the fake flag to be set in the first place
    <teythoon> that's why i put the assertion in ;)
    <braunr> on the other hand, you check the refcnt precisely because other
      threads may have reacquired the node
    <teythoon> but why would moving the assertion change anything ?
    <teythoon> if we would do that, we'd "lose" all threads that see
      np->reference being >1
    <teythoon> but for those objects the fake_reference flag should never be
      set anyways
    <teythoon> i cannot see why this would help
    <teythoon> (does it help ?)
    <teythoon> (and if it does, it points to a serious problem imho)
    <braunr> i'm recreating the traces that made me think that
    <braunr> to get a clearer view of what's happening
    <braunr> the problem i have with the current code is this
    <braunr> there can be multiple protid referring to the same node occurring
      at the same time
    <braunr> they are serialized by the hash table lock, ok
    <braunr> but there apparently are cases where the first (of two) protids
      being closed sets the fakeref flag
    <braunr> and the following chokes because the flag is set
    <braunr> i assume you put this refcount check because you assumed only the
      last protid being closed can set the flag, right ?
    <braunr> but then, why > 1 ? why not > 0 ?
    <teythoon> yes, that's what i was trying to assert
    <teythoon> b/c the 1 is our reference
    <braunr> which one exactly ?
    <teythoon> >1 is anyone *beside* us
    <teythoon> ?
    <braunr> hm
    <braunr> you mean the reference held by the protid being destroyed
    <teythoon> yes
    <braunr> isn't that reference already dropped before calling the cleanup
      function ?
    <braunr> ah no, it's the node ref
    <teythoon> yes
    <braunr> released by netfs_release_protid
    <teythoon> exactly
    <braunr> which is called without the hash table lock held
    <braunr> hm no
    <braunr> it's locked
    <braunr> damn my brain is slow today
    <teythoon> i actually think that it's the combination of manual reference
      counting and the primitive concurrency model that makes it hard to reason
      about this
    <braunr> well
    <braunr> the model is quite simple too
    <braunr> accesses to refcounters must be protected by the appropriate lock
    <braunr> this isn't done here, on the assumption that all referencing
      operations are protected by another global lock all the time
    <teythoon> even if a model is simple, this does not mean that it is a good
      model for human beings to comprehend and reason about
    <braunr> i don't know
    <braunr> note that netfs_drop_node is designed to be called with
      netfs_node_refcnt_lock locked
    <braunr> implying the refcount must remain stable between checking it and
      dropping the node
    <braunr> netfs_make_peropen is called without the hash table lock held in
      dir_lookup
    <braunr> and this increases the refcount
    <braunr> although the problem is rather that something decreases it without
      the lock held
    <teythoon> we should port libtsan and just ask gcc -fsanitize=thread
    <braunr> what about the netfs_nput call at the end of dir_lookup ?
    <braunr> the fake ref should be set by the norefs function
    <teythoon> that should not decrease the count to 0 b/c the caller holds a
      reference too
    <braunr> yes that's ugly
    <braunr> ugh
    <braunr> i'm unable to think clearly right now
    <teythoon> as mentioned in the commit message, you cannot do something like
      this in the norefs function
    <teythoon> bbl ;)
    <braunr> bye teythoon 
    <braunr> thanks for your time
    <braunr> for when you come back :
    <braunr> instead of maintaining this "fake" reference, why not assumeing
      the hash table holds a reference, and simply count it
    <braunr> the same way a cache does
    <braunr> and drop that reference when removing a node, either to reflect
      the current state of the underlying node, or because the translator is
      being shut down ?
    <braunr> why not assume*
    <braunr> bbl too
    <teythoon> sure, refactoring is definitively an option


## IRC, freenode, #hurd, 2014-01-24

    <braunr> teythoon: ok, i'll take care of fakeroot
    <teythoon> braunr: thanks. tbh i was a little fed up with that little
      bugger >,<
    <braunr> i can imagine
    <braunr> considering the number of patches you've sent already

    <braunr> teythoon: are you sure about your call to fshelp_lock_init ?
    <teythoon> yes, why do you ask ?
    <teythoon> (the test case is given in the commit message)
    <braunr> it doesn't look right to me to call "init" while the node is
      potentially locked
    <braunr> i noticed libdiskfs peropen release function takes care of
      releasing locks
    <braunr> it looks better to me
    <teythoon> it's not about releasing the lock
    <teythoon> it's about faking the file being closed which implicitly
      releases the lock
    <braunr> the file is being close
    <braunr> closed
    <braunr> since it's in the cleanup function
    <teythoon> yes, but we keep it b/c the file has faked attributes
    <teythoon> did you look at the problem description in the commit message ?
    <braunr> we keep the node
    <braunr> not the peropen
    <teythoon> so ?
    <teythoon> the lock is in the node
    <braunr> why would libdiskfs do it in the peropen release then ?
    <braunr> there is an inconsistency somwhere
    <braunr> actually, the lock looks to be per open
    <braunr> or rather, the lock is per node, but its status is recorded per
      open
    <braunr> allowing the implementation to track if a file descriptor was used
      to install a lock and release it when that file descriptor goes away
    <teythoon> why would the node be locked ?
    <teythoon> locked in what way, file-locking locked ?
    <braunr> yes
    <braunr> posix explicitely says that file locks must be implicitely removed
      when closing the file descriptor used to install them, so that makes
      sense
    <teythoon> isn't hat exactly what i'm doing ?
    <braunr> no
    <braunr> you're initializing the file lock
    <braunr> init != unlock
    <braunr> and it's specific to fakeroot, while it looks like libnetfs should
      be doing it
    <teythoon> libnetfs would do it
    <teythoon> but we prevent that by keeping the node alive
    <braunr> again, it's a per open thing
    <braunr> and no, libnetfs doesn't release locks implicitely in the current
      version
    <teythoon> didn't we agree that for fakeroot one peropen object is
      associated with one protid object ?
    <braunr> yes
    <braunr> and don't keep those alive
    <braunr> so let them die peacefully, and fix libnetfs so it releases the
      lock as it's supposed to
    <braunr> and we* don't
    <teythoon> we don't keep those alive
    <teythoon> why would we ?
    <braunr> yes that's what i wanted to say
    <braunr> what i mean is
    <braunr> since letting peropens die is already what is being done
    <braunr> there is no need for a special handling of locks in fakeroot
    <teythoon> oh
    <braunr> on the other hand, libnetfs must be fixed
    <teythoon> ok, that might very well be true
    <teythoon> (we need to bring libnetfs and diskfs closer so that they can be
      diff'ed easily)
    <braunr> i just wanted to check your reason for using lock_init in the
      first place
    <braunr> yes ..
    <braunr> teythoon: also, i think we actually do have what's necessary to
      deal with garbage collection
    <braunr> namely, dead-name notifications
    <braunr> i'll see if i can cook something simple enough
    <braunr> otherwise, merely keeping every node around is also acceptable
      considering the use cases
    <teythoon> dead-name notifications won't help if the real node disappears,
      no ?
    <braunr> teythoon: dead name notifications on the real node port :)
    <braunr> teythoon: at least i can reliably build the hurd package using
      fakeroot-hurd now
    <braunr> let's try glibc :)

## IRC, freenode, #hurd, 2014-01-25

    <teythoon> braunr: awesome :)
    <braunr> teythoon: hm not sure :/
    <braunr> darnassus got oom
    <braunr> teythoon: could be unrelated though
    <braunr> teythoon: something has apprently made /home unresponsive :(
    <braunr> teythoon: i suspect bots hitting apache and in particular the git
      repositories to have increased memory usage


## IRC, freenode, #hurd, 2014-01-26

    <braunr> teythoon: btw, fakeroot interacts very very badly with other netfs
      file systems
    <braunr> e.g., listing /proc through it creates lots of nodes
    <braunr> i'm not yet sure how to fix that
    <braunr> using a dead name notification doesn't seem appropriate (at least
      not directly) because fakeroot holds a true reference that prevents the
      deallocation of the target node


## IRC, freenode, #hurd, 2014-01-27

    <braunr> teythoon: good news (more or less): fakeroot is actually leaking a
      lot when crossing file systems
    <braunr> which means if i fix that, there is a good chance we can use it to
      build all packages with it
    <braunr> -with it
    <teythoon> what do you mean exactly ?
    <braunr> if target nodes are from /, there is no such leak
    <braunr> as soon as the target nodes are from another file system, ports
      rights are leaked
    <braunr> that's what fills the kernel allocator actually
    <teythoon> oh, so dir_lookup leaks ports when crossing translator
      boundaries ?
    <braunr> seems so
    <teythoon> yeah, that might very well be it
    <teythoon> the dir_lookup logic in lib*fs is quite involved :/
    <braunr> yes, my simple attempts were unsuccessful
    <braunr> but i'm confident i can fix it soon
    <teythoon> that sounds good :)
    <braunr> i also remove the fake_ref flag and replace it with "accounting
      the reference in the hash table" as soon as a node is faked
    <teythoon> fine with me
    <braunr> these will be the expected leak
    <braunr> but they're far less in numbers than what i observe
    <braunr> and garbage collection can be implemented later
    <braunr> although i would prefer notifications a lot more
    <braunr> end of the news, bbl :)
    <braunr> found it :>
    <teythoon> braunr: -v ;)
    <braunr> err = dir_lookup (...);
    <braunr> if (dir != dnp->nn->file) mach_port_deallocate (mach_task_self (),
      dir);
    <braunr> in other words, deallocate ports for intermediate file system root
      directories .. :)
    <braunr> teythoon: currently building hurd and glibc packages
    <braunr> but i intend to improve some more with the addition of a default
      faked state
    <braunr> so that only nodes with modified faked states are retained
    <teythoon> how do you mark nodes as having the default faked state ?
    <braunr> i don't
    <teythoon> ok, right, makes sense :)
    <teythoon> this sounds awesome, thanks for following up on this
    <braunr> i'm quite busy with other stuff so, with proper testing, it should
      take me the week to get merged
    <braunr> teythoon: well thanks for all the fixes you've done
    <braunr> fakeroot was completely unusable before that
    <teythoon> if you push your changes somewhere i'll integrate them into my
      packages and test them
    <braunr> ok
    <braunr> implementing fakeroot -u could also be a good thing
    <braunr> and this should work easily with that default faked state strategy


## IRC, freenode, #hurd, 2014-01-28

    <braunr> teythoon: i should be able to test fakeroot-hurd with the default
      faked attributes strategy today on glibc
    <teythoon> braunr: very nice :)
    <braunr> azeem_: do you happen to know if fakeroot -u is used by debian ?
    <braunr> i mean when building packages
    <teythoon> braunr: how does fakeroot-hurd perform on darnassus ?
    <teythoon> i mean, does it yield a noticeable improvement over fakeroot-tcp
      just like on my slow box ?
    <braunr> i'm not measuring that :/
    <teythoon> ok, no problem
    <braunr> and since nodes are removed from the hash table, performance might
      decrease slightly
    <braunr> but the number of rights is kept very low, as expected
    <teythoon> that's good
    <braunr> i keep seeing leaks though
    <braunr> when switching cwd between file systems
    <teythoon> humm
    <braunr> so i assume something is wrong with the identity of . or ..
    <braunr> it's so insignificant compared to the previous problems that i
      won't waste time on that
    <braunr> teythoon: the problem with measuring on darnassus is that it's a
      public machine
    <teythoon> right
    <braunr> often scanned by ssh worms or http bots

[[cannot_create__dev_null__interrupted_system_call]].

    <braunr> but it makes complete sense to get better performance with
      fakeroot-hurd
    <braunr> that's actually one of the reasons i'm working on it
    <braunr> if not the main one
    <teythoon> :)
    <teythoon> that was my motivation too
    <braunr> it shows how you can get an interchangeable unix tool that
      directly plugs well with the low level system
    <braunr> and make it work better
    <teythoon> nicely put :)

    <braunr> teythoon: i still can't manage to build glibc with fakeroot-hurd
    <braunr> but i'm not sure why :/
    <braunr> there was no kernel memory exhaustion this time
    <teythoon> :/
    <braunr> cp: cannot create regular file `debian/libc-bin.dirs': Permission
      denied
    <braunr> hum
    <braunr> youpi: do you know if building debian packages requires fakeroot
      -u option ?
    <youpi> I don't know
    <gg0> braunr: man dpkg-buildpackage says it just runs "fakeroot
      debian/rules <target>"
    <gg0> sources confirm that
      http://sources.debian.net/src/dpkg/1.17.6/scripts/dpkg-buildpackage.pl#L465
    <braunr> gg0: ok


## IRC, freenode, #hurd, 2014-01-29

    <braunr> it seems that something sets the permissions of this
      debian/libc-bin.dirs file to 000 ...
    <teythoon> i've seen this too
    <braunr> oh
    <braunr> do you think it's a fakeroot-hurd bug ?
    <teythoon> have i mentioned something like this in a commit message ?
    <teythoon> yes
    <teythoon> it is
    <braunr> ok
    <braunr> i didn't see any mention of it
    <braunr> but i could have missed it
    <teythoon> hm, i cannot recall it either
    <teythoon> but i've seen this issue with fakeroot-hurd
    <braunr> ok
    <braunr> it's probably the last issue to fix to get it to work for our
      packages
    <braunr> teythoon: i think i have a solution for that last mode bug
    <braunr> fakeroot doesn't relay chmod requests, unless they change an
      executable bit
    <braunr> i don't see the point, and simply removed that condition to relay
      any chmod request
    <teythoon> braunr: did it work ?
    <braunr> no
    <braunr> fakeroot still consumes too many ports
    <braunr> and for each file, there are at least two ports, the faked one,
      and the real one
    <braunr> it should be completely reworked
    <braunr> but i don't have time to do that
    <braunr> i'll see if it works when building from scratch
    <braunr> actually, it's not even a quantity problem but a fragmentation
      problem
    <braunr> the function that fails is kmem_realloc ..
    <braunr> ipc spaces are arrays in kernel space ....
    <teythoon> it's more like three ports per file, you forgot the identity
      port
    <braunr> ah yes


## IRC, freenode, #hurd, 2014-02-03

    <braunr> teythoon: i'll commit my changes on fakeroot tonight
    <braunr> they do improve the tool, but not enough to build glibc with it
    <teythoon> braunr: cool :), so how do we make it fully usable ?
    <braunr> teythoon: i don't know ..
    <braunr> i'll try re adding detection of nodes with no hard links for one
    <braunr> but imho, it needs a rework based on what the real fakeroot does
    <braunr> i won't work on it though

    <braunr> teythoon: also, it looks like i've tested building glibc with a
      wrong test binary of my fakeroot version :/
    <braunr> so consider all test results irrelevant so far


## IRC, freenode, #hurd, 2014-02-04

    <braunr> fakeroot-hurd might turn out to be easily usable for our debian
      packages with the fixed binary :)

    <braunr> teythoon: hum, can you explain
      672005782e57e049c7c8f4d6d0b2a80c0df512b4 (trans: fix locking issue in
      fakeroot) when you have time please ?
    <braunr> it looks like it introduces a deadlock by calling new_node (which
      acquires the hash table lock) while dir is locked, violating the hash
      table -> node locking order

    <teythoon> braunr: awesome, then there still is hope for fakeroot-hurd :)

    <braunr> teythoon: i've been able to build glibc packages several times
      this night
    <braunr> so except for this deadlock i've seen once, it looks good
    <teythoon> right
    <teythoon> that deadlock
    <teythoon> right, it does indeed violate the partial order of the locks :-/

    <braunr> teythoon: can you explain why you moved the lock in attempt_mkfile
      please ?

    <braunr> teythoon: i've just tested a fakeroot binary without the patch
      introducing the deadlock, and glibc built without any problem
    <teythoon> braunr: well, this is very good news :)
    <braunr> teythoon: but i still wonder why you made this patch in the first
      place, i don't want to revert it blindly and reintroduce a potential
      regression
    <teythoon> braunr: i thought i was fixing the order in which locks were
      taken. if the commit message does not specify that it fixes an issue,
      then i was probably just wrong and you can revert it
    <braunr> oh ok
    <braunr> good

    <braunr> teythoon: another successful build :)
    <braunr> i'll commit my changes
    <teythoon> awesome :)
    <braunr> there might still be concurrency issues but it's much better
    <teythoon> i'm curious what you did :)
    <braunr> so little :)
    <braunr> i was sick all week heh
    <braunr> you'll se
    <braunr> see
    <teythoon> well, that's good actually ;)
    <braunr> yes

    <braunr> teythoon: actually there was another debugging line left over, and
      again, my test results are irrelevant @#!


## IRC, freenode, #hurd, 2014-02-05

    <braunr> teythoon: i got an assertion about nn->np->nn not being equal to
      nn atfer the hash table lookup is dir_lookup
    <braunr> +failure
    <teythoon> that's bad
    <braunr> not over yet
    <teythoon> i had a couple of those too
    <teythoon> i guess it's a use after free
    <braunr> yes
    <teythoon> i used to poison the pointers and comment out the frees to track
      them down iirc
    <braunr> teythoon: one of your patches stores netnodes instead of nodes in
      the hash table, citing some overwriting issue
    <braunr> teythoon: i don't understand why using netnodes fixes this
    <teythoon> braunr: libihash has this cookie for fast deletes
    <teythoon> that has to be stored somewhere
    <teythoon> the node structure has no room for it
    <braunr> uh
    <teythoon> yes
    <teythoon> it was that bad
    <braunr> ...
    <teythoon> hence the uglyish back pointers
    <braunr> i see
    <teythoon> looking back i cannot even say why it worked at all
    <braunr> well, it didn't
    <teythoon> i believe libihash must have destroyed a linked list in the node
      struct
    <braunr> possibly
    <teythoon> no, it did not >,<, but for simple tests it kind of did
    <braunr> yes fakeroot sometimes corrupts memory badly ....
    <braunr> and yes, turns out the assertion is triggered on nodes with 0 refs
      ..
    <braunr> teythoon: it looks like even the current version makes wrong usage
      of the ihash interface
    <braunr> locp_offset is defined as "The offset of the location pointer from
      the hash value"
    <braunr> and indeed, it's an intptr_t
    <braunr> teythoon: hm no, it looks ok actually, forget what i said :)
    <teythoon> *phew
    <teythoon> :p

    <braunr> hmm, still occasional double frees in fakeroot, but it looks in
      good shape for single threaded tasks like package building

    <braunr> teythoon: i've just sent my fakeroot patches
    <teythoon> braunr: sweet, i'll have a closer look tomorrow :)
    <braunr> teythoon: i couldn't debug the double frees though :/


## IRC, freenode, #hurd, 2014-02-06

    <braunr> btw, i'm able to successfully use fakeroot-hurd to build glibc
      packages, but is there a way to make sure the resulting archives contain
      the right privileges and ownerships ?
    <youpi> I don't remember whether debdiff checks permissions

    <youpi> braunr: I've just got  fakeroot-hurd debian/rules clean
    <youpi> dh_clean 
    <youpi> fakeroot: ../../trans/fakeroot.c:161: netfs_node_norefs: Assertion
      `np->nn->np == np' failed.
    <youpi> while building eglibc
    <teythoon> youpi: yes, that lockup is most annoying... :/
    <braunr> youpi: with the new version ?
    <youpi> yes
    <braunr> hum
    <braunr> i only had rare double frees, not that any more :/
    <braunr> youpi: ok i got the error too
    <braunr> still not good enough
    <youpi> ok


## IRC, freenode, #hurd, 2014-02-07

    <braunr> youpi: debdiff seems to handle permissions
    <braunr> i've found the cause of the assertions
    <youpi> braunr: groovie :)


## IRC, freenode, #hurd, 2014-02-08

    <teythoon> braunr: nice :)
    <braunr> http://darnassus.sceen.net/~rbraun/debdiff_report


## IRC, freenode, #hurd, 2014-02-10

    <braunr> and, on a completely different topic, here is a crash i can
      reproduce when using fakeroot:
      http://darnassus.sceen.net/~rbraun/fakeroot_hurd_rpctrace_o_var_tmp_out_rm_rf_dir.png


## IRC, freenode, #hurd, 2014-02-11

    <braunr> still working on fakeroot
    <braunr> there are still races (not disturbing for package building but
      still ..)
    <braunr> there may be wrong right handling
    <teythoon> i believe i have witnessed a fakeroot deadlock :/
    <braunr> aw
    <teythoon> not sure though, buildbot killed the build process before i
      could investigate
    <braunr> teythoon: was it a big package ?
    <teythoon> half of the hurd package
    <braunr> that's not a port right overflow then


## IRC, freenode, #hurd, 2014-03-05

    <teythoon> youpi: what about the exec_filename patch series? even though
      fakeroot still has some issues (has it?), i consider it worthy for
      inclusion

[[glibc#execve_relative_paths]].

    <youpi> Roland was disagreeing with it
    <youpi> iirc the fakeroot issue was solved
    <teythoon> braunr: ^
    <braunr> fakeroot goot a lot more robust than it used to be
    <braunr> but i haven't checked that it actually behaves exactly like the
      library for corner cases
    <braunr> there are minor differences
    <braunr> also, it seems to trigger concurrency bugs in ext2fs
    <braunr> e.g. git reporting that files either "already exist" or "can't be
      found"
    <braunr> it happens (rarely) when directly using ext2
    <braunr> and more often through fakeroot
    <braunr> i didn't take the time to investigate

## youpi

    the daily script of debian-installer uses the -s / -i options of fakeroot. How could we manage to implement them?