open issue documentation: edit and move to FAQ.

IRC, freenode, #hurd, around 2010-09

<pinotree> (also, shouldn't /proc/version say something else than "Linux"?)
<youpi> to make linux tools work, no :/
<youpi> kfreebsd does that too
<pinotree> really?
<youpi> yes
<youpi> (kfreebsd, not freebsd)
<pinotree> does kbsd's one print just "Linux version x.y.z" too, or
  something more eg in a second line?
<pinotree> (as curiosity)
<youpi> % cat /proc/version
<youpi> Linux version 2.6.16 (des@freebsd.org) (gcc version 4.3.5) #4 Sun
  Dec 18 04:30:00 CET 1977
<pinotree> k

IRC, freenode, #hurd, 2013-06-04

<safinaskar> ?@?#@?$?@#???!?!?!?!??!?!?!?! why /proc/version on gnu system
  reports "Linux version 2.6.1 (GNU 0.3...)"?
<braunr> safinaskar: because /proc/version is a linux thing
<braunr> applications using it don't expect to see anything else than linux
  when parsing
<braunr> think of it as your web brower allowing you to set the user-agent
<safinaskar> braunr: yes, i just thought about user-agent, too
<safinaskar> braunr: but freebsd doesn't report it is linux (as well as i
<braunr> their choice
<braunr> we could change it, but frankly, we don't care
<safinaskar> so why "uname" says "GNU" and not "Linux"?
<braunr> uname is posix
<braunr> note that /proc/version also includes GNU and GNU Mach/Hurd
<safinaskar> if some program read the word "Linux" from /proc/version, it
  will assume it is linux. so, i think it is bad idea
<braunr> why ?
<safinaskar> there is no standard /proc across unixen
<braunr> if a program reads /proc/version, it expects to be run on linux
<safinaskar> every unix implement his own /proc
<safinaskar> so, we don't need to create /proc which is fully compatible
  with linux
<braunr> procfs doesn't by default
<safinaskar> instead, we can make /proc, which is partially compatible with
<braunr> debiansets the -c compatibility flag
<braunr> that's what we did
<safinaskar> but /proc/version should really report kernel name and its
<braunr> why ?
<braunr> (and again, it does)
<safinaskar> because this is why /proc/version created
<pinotree> no?
<braunr> on linux, yes
<braunr> pinotree: hm ?
<safinaskar> and /proc/version should not contain the "Linux" word, because
  this is not Linux
<braunr> pinotree: no to what ? :)
<braunr> safinaskar: *sigh*
<braunr> i explained the choice to you
<pinotree> safinaskar: if you are using /proc/version to get the kernel
  name and version, you're doing bad already
<braunr> disagree if you want
<braunr> but there is a point to using the word Linux there
<pinotree> safinaskar: there's the proper aposix api for that, which is
<safinaskar> pinotree: okey. so why we ever implement /proc/version?
<braunr> it's a linux thing
<braunr> they probably wanted more than what the posix api was intended to
<safinaskar> okey, so why we need this linux thing?   there is a lot of
  linux thing which is useful in hurd.  but not this thing.   because this
  is not linux.    if we support /proc/version, we should not write "Linux"
  to it
<pinotree> and even on freebsd their linprocfs (mounted on /proc) is not
  mounted by default
<braunr> 10:37 < braunr> applications using it don't expect to see anything
  else than linux when parsing
<braunr> 10:37 < braunr> think of it as your web brower allowing you to set
  the user-agent
<braunr> safinaskar: the answer hasn't changed
<safinaskar> pinotree: but they don't export /proc/version with "Linux"
  word in it anyway
<pinotree> safinaskar: they do
<safinaskar> pinotree: ??? their /proc/version contain Linux?
<pinotree> Linux version 2.6.16 (des@freebsd.org) (gcc version 4.6.3) #4
  Sun Dec 18 04:30:00 CET 1977
<kilobug> safinaskar: it's like all web browsers reporting "mozilla" in
  their UA, it may be silly, but it's how it is for
  compatibility/historical reasons, and it's just not worth the trouble of
  changing it
<pinotree> that's on a debian gnu/kfreebsd machine
<pinotree> and on a freebsd machine it is the same
<braunr> safinaskar: you should understand that parsing this string allows
  correctly walking the rest of the /proc tree
<pinotree> and given such filesystem on freebsd is called "linprocfs", you
  can already have a guess what it is for
<kilobug> safinaskar: saying "Linux version 2.6.1" just means "I'm
  compatible with Linux 2.6.1 interfaces", like saying "Mozilla/5.0 (like
  Gecko)" in the UA means "I'm a modern browser"
<safinaskar> so, is there really a lot of programs which expect "Linux"
  word in /proc/version even on non-linux platforms?
<braunr> no
<braunr> but when they do, they do


IRC, freenode, #hurd, around 2010-09

<youpi> jkoenig: is it not possible to provide a /proc/self which points at
  the client's pid?
<pinotree> looks like he did 'self' too, see rootdir_entries[] in rootdir.c
<youpi> but it doesn't point at self
<antrik> youpi: there is no way to provide /proc/self, because the server
  doesn't know the identity of the client
<youpi> :/
<antrik> youpi: using the existing mechanisms, we would need another magic
  lookup type
<antrik> an alternative idea I discussed with cfhammer once would be for
  the client to voluntarily provide it's identity to the server... but that
  would be a rather fundamental change that requires careful consideration
<antrik> also, object migration could be used, so the implementation would
  be provided by the server, but the execution would happen in the
  client... but that's even more involved :-)
<youpi> but we've seen how much that'd help with a lot of other stuff
<antrik> I'm not sure whether we discussed this on the ML at some point, or
  only on IRC
<youpi> it "just" needs to be commited :)
<antrik> in either case, it can't hurt to bring this up again :-)

discussion, IRC, freenode, #hurd, 2013-09-07. Look at [glibc]/hurd/lookup-retry.c for how FS RETRY MAGICAL lookups work.

root group

IRC, freenode, #hurd, around October 2010

<pinotree> the only glitch is that files/dirs have the right user as
  owner, but always with root group

/proc/[PID]/stat being 400 and not 444, and some more

IRC, freenode, #hurd, 2011-03-27

<pochu> is there a reason for /proc/$pid/stat to be 400 and not 444 like on
<pochu> there is an option to procfs to make it 444 like Linux
<pochu> jkoenig: ^
<jkoenig> pochu, hi
<jkoenig> /proc/$pid/stat reveals information which is not usually
  available on Hurd
<jkoenig> so I made it 400 by default to avoid leaking anything
<pochu> is there a security risk in providing that info?
<jkoenig> probably not so much, but it seemed like it's not really a
  descision procfs should make
<jkoenig> I'm not sure which information we're speaking about, though, I
  just remember the abstract reason.
<pochu> things like the pid, the memory, the priority, the state...
<pochu> sounds safe to expose
<jkoenig> also it's 0444 by default in "compatible" mode
<jkoenig> (which is necessary for the linux tools to work well)
<pochu> yeah I saw that :)
<pochu> my question is, should we change it to 0444 by default? if there
  are no security risks and this improves compatibility, sounds like a good
  thing to me
<pochu> we're already 'leaking' part of that info through e.g. ps
<jkoenig> I think /proc should be translated by /hurd/procfs --compatible
  by default (I'm not sure whether it's already the case)
<jkoenig> also I'm not sure why hurd-ps is setuid root, rather than the
  proc server being less paranoid, but maybe I'm missing something.
<pochu> jkoenig: it's not, at least not on Debian
<pochu> youpi: hi, what do you think about starting procfs with
  --compatible by default?
<pochu> youpi: or changing /proc/$pid/stat to 0444 like on Linux
  (--compatible does that among a few other things)
<youpi> I guess you need it for something?
<pochu> I'm porting libgtop :)
<youpi> k
<pochu> though I still think we should do this in procfs itself
<youpi> ymmv
<jkoenig> pochu, youpi, --compatible is also needed because mach's high
  reported sysconf(_SC_CLK_TCK) makes some integers overflow (IIRC)
<youpi> agreed
<jkoenig> luckily, tools which use procfs usually try to detect the value
  /proc uses rather than rely on CLK_TCK
<jkoenig> (so we can choose whatever reasonable value we want)

IRC, freenode, #hurd, 2011-03-28

<antrik> jkoenig: does procfs expose any information that is not available
  to everyone through the proc server?...
<antrik> also, why is --compatible not the default; or rather, why is there
  even another mode? the whole point of procfs is compatibility...
<jkoenig> antrik, yes, through the <pid>/environ and (as mentionned above)
  <pid>/stat files, but I've been careful to make these files readable only
  to the process owner
<jkoenig> --compatible is not the default because it relaxes this paranoia
  wrt. the stat file, and does not conform to the specification with regard
  to clock tick counters
<antrik> what specification?
<jkoenig> the linux proc(5) manpage
<jkoenig> which says clock tick counters are in units of
<antrik> so you are saying that there is some information that the Hurd
  proc server doesn't expose to unprivileged processes, but linux /proc
<jkoenig> yes
<antrik> that's odd. I wonder what the reasoning behind that could be
<antrik> but this information is available through Hurd ps?
<antrik> BTW, what exactly is _SC_CLK_TCK supposed to be?
<pinotree> jkoenig: hm, just tried with two random processes on linux
  (2.6.32), and enrivon is 400
<pinotree> (which makes sense, as you could have sensible informations eg
  in http_proxy or other envvars)
<jkoenig> antrik, CLK_TCK is similar to HZ (maybe clock resolution instead
  of time slices ?)
<jkoenig> sysconf(3) says "The number of clock ticks per second."
<jkoenig> antrik, I don't remember precisely what information this was, but
  ps-hurd is setuid root.
<jkoenig> anyway, if you run procfs --compatible as a user and try to read
  foo/1/stat, the result is an I/O error, which is the result of the proc
  server denying access.
<antrik> but Linux /proc acutally uses HZ as the unit IIRC? or is
  _SC_CLK_TCK=HZ on Linux?...
<jkoenig> I expect they're equal.
<jkoenig> in practice procps uses heuristics to guess what value /proc uses
  (for compatibility purposes with older kernels)
<jkoenig> I don't think HZ is POSIX, while _SC_CLK_TCK is specifies as the
  unit for (at least) the values returned by times()
<jkoenig> s/specifies/specified/
<jkoenig> antrik, some the information is fetched directly from mach by
  libps, and understandably, the proc server does not give the task port to
  anyone who asks.
<antrik> well, as long as the information is exposed through ps, there is
  no point in hiding it in procfs...
<antrik> and I'm aware of the crazy guessing in libproc... I was actually
  mentoring the previous procfs implementation
<antrik> (though I never got around to look at his buggy code...)
<jkoenig> ok

IRC, freenode, #hurd, 2011-07-22

<pinotree> hm, why /proc/$pid/stat is 600 instead of 644 of linux?
<jkoenig> pinotree, it reveals information which, while not that sensitive,
  would not be available to users through the normal proc interface.
<jkoenig> (it's available through the ps command which is setuid root)
<jkoenig> we discussed at some point making it 644, IIRC.
<pinotree> hm, then why is it not a problem on eg linux?
<jkoenig> (btw you can change it with the -s option.)
<jkoenig> pinotree, it's not a problem because the information is not that
  sensitive, but when rewriting procfs I preferred to play it self and
  consider it's not procfs' job to decide what is sensitive or not.
<jkoenig> IIRC it's not sensitive but you need the task port to query it.
<jkoenig> like, thread times or something.
<pinotree> status is 644 though
<jkoenig> but status contains information which anyone can ask to the proc
  server anyway, I think.

/proc/mounts, /proc/[PID]/mounts

IRC, freenode, #hurd, 2011-07-25

< pinotree> jkoenig: btw, what do you think about providing empty
  /proc/mounts and /proc/$pid/mounts files?
< jkoenig> pinotree, I guess one would have to evaluate the consequences
  wrt. existing use cases (in other words, "I have absolutely no clue
  whatsoever about whether that would be desirable" :-)
< jkoenig> pinotree, the thing is, an error message like "/proc/mounts: No
  such file or directory" is rather explicit, whereas errors which would be
  caused by missing data in /proc/mounts would maybe be harder to track
< braunr> this seems reasonable though
< braunr> there already are many servers with e.g. grsecurity or chrooted
  environments where mounts is empty
< pinotree> well, currently we also have an empty mtab
< braunr> pinotree: but what do you need that for ?
< braunr> pinotree: the init system ?
< pinotree> and the mnt C api already returns no entries (or it bails out,
  i don't remember)
< pinotree> not a strict need

A mtab translator now exists.

IRC, freenode, #hurd, 2013-09-20

<pinotree> teythoon: should procfs now have $pid/mounts files pointing to
<teythoon> pinotree: probably yes


Needed by glibc's pldd tool (commit 11988f8f9656042c3dfd9002ac85dff33173b9bd).


Needed by glibc's pldd tool (commit 11988f8f9656042c3dfd9002ac85dff33173b9bd).


id:"alpine.LFD.2.02.1110111111260.2016@akari". Needed by glibc's stdlib/tst-secure-getenv.c. HAVE_PROC_SELF_EXE in [GCC]/libjava/configure.ac. Also used in [GCC]/libgfortran/runtime/main.c:store_exe_path.

Is it generally possible to use something like the following instead? Disadvantage is that every program using this needs to be patched.

#include <dlfcn.h>
Dl_info DLInfo;
int err = dladdr(&main, &DLInfo);
if (err == 0)
/* Pathname of shared object that contains address: DLInfo.dli_fname.  */
/* Filter it through realpath.  */

This is used in [LLVM]/lib/Support/Unix/Path.inc.

IRC, OFTC, #debian-hurd, 2013-11-10

<mjt> Hello.  Does hurd have /proc/self/exe equivalent, to "re-exec myself"
<youpi> no, only argv[0]
<mjt> busybox uses /proc/self/exe by default to re-exec itself when running
  one of its applets, or failing that, tries to find it in $PATH.  I guess
  it doesn't work on hurd... :)
<mjt> and argv0 is unreliable
<youpi> some discussion on the hurd wiki talks about using Dl_info DLInfo
<youpi> which contains DLInfo.dli_fname
<youpi> err, I mean, callling dladdr(&main, &DLInfo);
<youpi> this is kernel-agnostic, provided one uses glibc
<mjt> um. -ldl. nice for static linking
<mjt> gcc t.c -ldl -static
<mjt> ./a.out 
<mjt> fname=AVA� �j
<mjt> bah :)
<mjt> (it just prints dli_fname)
<teythoon> :/
<youpi> ah, yes, that won't work with static linking
<teythoon> fixing /proc/self is on my todo list, it shouldn't be too hard
<youpi> since in that case it's the exec server which sets the process up,
  not dl.so
<teythoon> but we do not have the exe link either
<mjt> (the above test run was on linux not on hurd, fwiw_
<mjt> )


IRC, freenode, #hurd, 2012-04-24

<antrik> braunr: /proc/*/fd can be implemented in several ways. none of
  them would require undue centralisation
<antrik> braunr: the easiest would be adding one more type of magic lookup
  to the existing magic lookup mechanism
<antrik> wait, I mean /proc/self... for /proc/*/fd it's even more
  straighforward -- we might even have a magic lookup for that already
<pinotree> i guess the ideal thing would be implement that fd logic in
<antrik> pinotree: nope. it doesn't need to ask proc (or any other server)
  at all. it's local information. that's what we have the magic lookups for
<antrik> one option we were considering at some point would be using the
  object migration mechanism, so the actual handling would still happen
  client-side, but the server could supply the code doing it. this would
  allow servers to add arbitrary magic lookup methods without any global
  modifications... but has other downsides :-)
<gnu_srs> youpi: How much info for /proc/*/fd is possible to get from
  libps? Re: d-h@
<youpi> see my mail
<youpi> I don't think there is an interface for that
<youpi> processes handle fds themselves
<youpi> so libps would have to peek in there
<youpi> and I don't remember having seen any code like that
<gnu_srs> 10:17:17< antrik> wait, I mean /proc/self... for /proc/*/fd it's
  even more straighforward -- we might even have a magic lookup for that
<gnu_srs> pinotree: For me that does not ring a bell on RPCs. Don't know
  what magic means,,
<youpi> for /proc/self/fd we have a magic lookup
<youpi> for /proc/pid/fd, I don't think we have
<gnu_srs> magic lookup*
<gnu_srs> magic lookup == RPC?
<youpi> magic lookup is a kind of answer to the lookup RPC
<youpi> that basically says "it's somewhere else, see there"
<youpi> the magic FD lookup tells the process "it's your FD number x"
<youpi> which works for /proc/self/fd, but not /proc/pid/fd
<civodul> youpi, gnu_srs: regarding FDs, there the msg_get_fd RPC that
  could be used
<civodul> `msgport' should have --get-fd, actually
<youpi> civodul: I assumed that the reason why msgport doesn't have it is
  that it didn't exist
<youpi> so we can get a port on the fd
<youpi> but then how to know what it is?
<civodul> youpi: ah, you mean for the /proc/X/fd symlinks?
<civodul> good question
<civodul> it's not designed to be mapped back to names, indeed :-)
<antrik> youpi: yeah, I realized myself that only /proc/self/fd is trivial
<antrik> BTW, in Linux it's nor real symlinks. it's magic, with some very
  strange (but useful in certain situations) semantics
<antrik> not real symlinks
<antrik> it's very weird for example for fd connected to files that have
  been unlinked. it looks like a broken symlink, but when dereferencing
  (e.g. with cp), you get the actual file contents...


GNU Savannah bug #32770

IRC, OFTC, #debian-hurd, 2012-06-20

<pinotree> bdefreese: the two elfutils tests fail because there are no
  /proc/$pid/maps files
<pinotree> that code is quite relying on linux features, like locating the
  linux kernel executables and their modules, etc
<pinotree> (see eg libdwfl/linux-kernel-modules.c)
<pinotree> refactor elfutils to have the linux parts executed only on linux
<bdefreese> Oh yeah, the maintainer already seems really thrilled about
  Hurd..  Did you see
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=662041 ?
<pinotree> kurt is generally helpful with us (= hurd)
<pinotree> most probably there he is complaining that we let elfutils build
  with nocheck (ie skipping the test suite run) instead of investigate and
  report why the test suite failed


HAVE_PROC_SELF_MAPS in [GCC]/libjava/configure.ac. Also used in [GCC]/intl/relocatable.c:find_shared_library_fullname for #ifdef __linux__.

IRC, freenode, #hurd, 2013-10-03

<camm`> what's the equivalent of cat /proc/self/maps on hurd?
<braunr> camm`: for now, /proc/self doesn't work as expected
<camm`> thanks, I just want to get a list of maps and protection status for
  a running process -- how?
<braunr> vminfo
<camm`> thanks so much!  I'm trying to debug an unexec failure on hurd when
  a linker script is present.  All works with the default script, but when
  the text address is changed, unexec fails, running into a page with no
  access in the middle of the executable:    0xc4b000[0x1000] (prot=0,
  max_prot=RWX, offs=0xb55000)
<camm`> I get a segfault when trying to read from this page.
<braunr> unexec ?
<camm`> emacs/gcl/maxima/acl2/hol88/axiom use unexec to dump a running
  image into a saved executable elf file.
<braunr> what is unexec ?
<braunr> ok looks like a dirty tool
<braunr> camm`: what is segfaulting, unexec or the resulting executable ?
<camm`> unexec opens the file from which the running program was originally
  executed, finds its section start addresses, then writes a new file
  replacing any data in the old file with possibly modified versions in
  running memory.  The reverse of 'exec'.
<camm`> the read from running memory delimited by the addresses in the
  executable file is hitting a page which has been protected with *no*
  access, and is segfaulting.  Somehow, when the binary file is loaded,
  hurd turning off all rights to this page.
<camm`> let me check the stack location ...
<camm`> ok I think I've got it -- hurd moves the sbrk(0) address away from
  the end of .data (as reported by readelf) if the addresses are low,
  presumably to avoid running into the stack.
<camm`> starting sbrk(0)!=.data+data_size on hurd
<braunr> i'm not sure there is anything like the heap on the hurd
<braunr> sbrk is probably implemented on top of mmap
<braunr> camm`: hm no, i'm wrong, glibc implements brk and sbrk mostly as
  expected, but remapping the area isn't atomic
<braunr> "Now reallocate it with no access allowed"
<braunr> then, there is a call to vm_protect
<braunr> and no error checking
<braunr> ...
<camm`> ok, that's fine, but need to know -- in general there is no
  relationship between the address returned by sbrk(0) and the .data
  addresses reported by readelf on the file, (hurd only) yes?
<braunr> i don't know about that
<braunr> there should be ..
<camm`> Specific example: readelf -a ->   [24] .data             PROGBITS
  000f5580 0c4580 000328 00  WA  0   0 32
<camm`> sbrk(0)->(void *) 0x8021000
<braunr> camm`: is that on an executable or a shared object ?
<camm`> executable
<braunr> 000f5580 looks very low
<camm`> This is using a linker script.  The default setup works just fine.
<camm`> I think it (might) make sense for hurd to silently do this give the
  placement of the C stack, but the assumptions behind my algorithm need
  changing (perhaps). 
<camm`> (I probe in configure the allowable range of __executable_start,
  and then choose a value to either ensure a large free signed range around
  NULL, or a low data start to maximize heap)
<camm`> braunr: are there any guarantees of sbrk(0)==.data+size without a
  linker script?
<braunr> camm`: i'm not sure at all
<braunr> sbrk isn't even posix
<camm`> thanks

IRC, freenode, #hurd, 2014-02-22

<ignaker> i'm trying to implement proc/maps 
<ignaker> actually I can't well evaluate complexity of tasks. However, I
  appreciate your comments
<braunr> the complexity can be roughly estimated from the number of
  components involved
<braunr> proc/maps involves procfs, ports, virtual memory, and file systems
<braunr> the naive implementation would merely be associating names to
  memory objects, and why not, but a more complete one would go ask file
  system servers about them
<braunr> perhaps more
<braunr> although personally i'd go for the naive one because less
  dependencies usually means better reliability
<braunr> something similar to task_set_name could do the job


Needed by glibc's pldd tool (commit 11988f8f9656042c3dfd9002ac85dff33173b9bd).


IRC, freenode, #hurd, 2012-06-30

* pinotree has a local work to add the /proc/$pid/cwd symlink, but relying
    on "internal" (but exported) glibc functions

CPU Usage

IRC, freenode, #hurd, 2013-01-30

<gnu_srs> Hi, htop seems to report CPU usage correct, but not top, is that
  a known issue? 
<youpi> does your /proc have the -c flag?
<gnu_srs> /hurd/procfs -c
<youpi> I don't remember which way it works, but iirc depending on whether
  -c is there or not, it will work or not
<youpi> problem being that nothing says linux' clock is 100Hz, but a lot of
  programs assume it
<gnu_srs> seems like htop gets it right though
<youpi> possibly just by luc
<youpi> k

IRC, freenode, #hurd, 2013-01-31

<braunr> both htop and top seem to have problems report the cpu time
<braunr> so i expect the problem to be in procfs

IRC, freenode, #hurd, 2013-10-03

<braunr> teythoon: any reason the static variable translator_exists isn't
  protected by a lock in procfs/rootdir.c ?

IRC, freenode, #hurd, 2013-10-04

<braunr> teythoon: can you tell me why translator_exists isn't protected
  from shared access in rootdir_mounts_exists ?
<teythoon> braunr: hm, dunno tbh, I probably thought the race was harmless
<braunr> it probably is
<braunr> settrans -Rg doesn't work on procfs :(

Kernel PID

IRC, freenode, #hurd, 2013-09-25

<braunr> hm cute, htop layout has become buggy, top just won't start
<teythoon> braunr: make sure your procfs knows the correct kernel pid
<teythoon> # showtrans /proc
<teythoon> /hurd/procfs -c -k 3
<teythoon> we could have handled this nicer if procfs were integrated
<teythoon> we should probably just update the default
<braunr> teythoon: mhm
<braunr> $ fsysopts /proc
<braunr> /hurd/procfs --stat-mode=444 --fake-self=1
<braunr> $ showtrans /proc
<braunr> /hurd/procfs -c
<pinotree> -c == --stat-mode=444 --fake-self=1
<braunr> better indeed
<braunr> teythoon: thanks

IRC, freenode, #hurd, 2013-10-04

<braunr> youpi: i fixed procfs on ironforge and exodar to be started as
  procfs -c -k 3
<braunr> without -k 3, many things as simple as top and uptime won't work

IRC, freenode, #hurd, 2013-10-24

<gg0> braunr: i'm using your repo and i can't see cpu percentage in htop
  anymore, all zeroes, confirmed?
<braunr> gg0: no
<braunr> gg0: you probably need to reset procfs
<braunr> gg0: settrans /proc /hurd/procfs -c -k 3