<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 (email@example.com) (gcc version 4.3.5) #4 Sun Dec 18 04:30:00 CET 1977 <pinotree> k
<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 know) <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 versions <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 linux <braunr> debiansets the -c compatibility flag <braunr> that's what we did <safinaskar> but /proc/version should really report kernel name and its version <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 uname <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 do <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 (firstname.lastname@example.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
<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.
<pinotree> the only glitch is that files/dirs have the right user as owner, but always with root group
<pochu> is there a reason for /proc/$pid/stat to be 400 and not 444 like on Linux? <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)
<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 1/sysconf(_SC_CLK_TCK) <antrik> so you are saying that there is some information that the Hurd proc server doesn't expose to unprivileged processes, but linux /proc does? <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
<pinotree> hm, why /proc/$pid/stat is 600 instead of 644 of linux? <jkoenig> pinotree, it reveals information which, while not that sensitive, would not be available to users through the normal proc interface. <jkoenig> (it's available through the ps command which is setuid root) <jkoenig> we discussed at some point making it 644, IIRC. <pinotree> hm, then why is it not a problem on eg linux? <jkoenig> (btw you can change it with the -s option.) <jkoenig> pinotree, it's not a problem because the information is not that sensitive, but when rewriting procfs I preferred to play it self and consider it's not procfs' job to decide what is sensitive or not. <jkoenig> IIRC it's not sensitive but you need the task port to query it. <jkoenig> like, thread times or something. <pinotree> status is 644 though <jkoenig> but status contains information which anyone can ask to the proc server anyway, I think.
< pinotree> jkoenig: btw, what do you think about providing empty /proc/mounts and /proc/$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.
<pinotree> teythoon: should procfs now have $pid/mounts files pointing to ../mounts? <teythoon> pinotree: probably yes
Needed by glibc's
pldd tool (commit
Needed by glibc's
pldd tool (commit
id:"alpine.LFD.2.02.1110111111260.2016@akari". Needed by glibc's
Also used in
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
<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 libps <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 already <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...
<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 :D <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
Also used in
Needed by glibc's
pldd tool (commit
* pinotree has a local work to add the /proc/$pid/cwd symlink, but relying on "internal" (but exported) glibc functions
<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
<braunr> both htop and top seem to have problems report the cpu time <braunr> so i expect the problem to be in procfs