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.

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.

< 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.

<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

discussion.

<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/gitweb/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

libpthread, 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

discussion.

<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.

<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