[[!meta copyright="Copyright © 2010, 2011, 2013 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] [[!tag open_issue_porting]] * * , * Will need to have something like Linux' [*cgroups*](http://git.kernel.org/gitweb.cgi?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/cgroups/cgroups.txt;hb=HEAD). Introduction: [*Ressourcen-Verwaltung mit Control Groups (cgroups)* (german)](http://www.pro-linux.de/artikel/2/1464/ressourcen-verwaltung-mit-control-groups-cgroups.html), Daniel Gollub, Stefan Seyfried, 2010-10-14. Likely there's also some other porting needed. # IRC, OFTC, #debian-hurd, 2011-05-19 pochu: http://news.gmane.org/gmane.comp.gnome.desktop - the "systemd as dependency" and all the messages in it don't give me a bright future for gnome on hurd... yeah, I've read the thread it's only a proposal so far... hopefully it'll be rejected, or they will only accept the interfaces that other OSes can implement... we'll see you can always help me with kde on hurd, would be nice ;) hehe pochu: well, even if the depenency is rejected, the whole «don't give a damn about non-linux and only bless linux for the "gnome os"» is a bit... worrying attitude yeah... it doesn't come from all the community though I'm sure some people have always thought that way Or we could get systemd going? :-) good luck with that :p tschwinge: haha!? :) That bad? tschwinge: if you mean by that forking indefinitely then maybe tschwinge: upstream has expressely stated multiple times, no interest whatsoever in any kind of portability to anything non-Linux or even older Linux versions! to the point of rejecting patches, because they "clutter" the source code... Well, then let's ``just'' implement the Linux interfaces. :-) tschwinge: then you'll be always playing catch up tschwinge: for example several of the Linux-only things upstream makes heavy use of, are pretty recent Linux-only additions to the kernel, but equivalents have been present on FreeBSD for years Yeah. I'm half-serious, half-joking. I haven't looked at the systemd code at all. https://mail.gnome.org/archives/desktop-devel-list/2011-May/msg00447.html for a list of its dependencies some are just glibc extensions though and some are IMO optional and should be conditionalized, but... pochu: I don't think that attitude is that old, there was a time when Linux was not used widely, or even that functional, I think it has been taking strength since the Linux Plumbers Cartel started :) as in one thing is not caring about anything non-Linux, the other is outright rejecting portability fixes tschwinge: in any case, these "recent" events are "pissing me off" to the point of having considered several times implementing portable replacements for some of those Utopia projects, the problem as always is time though :) tschwinge: and the issue is not only with systemd, upstart's upstream has the same approach to portability, if you want to port it, you'll have to maintain a fork let's create our own init system, make it better than anyone else, and when people start switching to it, let's start using hurd-only APIs :) We already had someone work on that. Like ten years ago. DMD. Daemon Managing Daemons. the real problem with that attitude is not the lack of care for portabilty, the real problem is that these people are pushing for their stuff all over the stack, and most of the time deprecating their own stuff after a while when they have rewritten it from scratch, leaving the burden of maintaining the old stuff to the other ports witness HAL, ConsoleKit, etc etc (anyway enough ranting I guess :) Yeah, it's true, though. agreed ## IRC, freenode, #hurd, 2013-01-18 systemd relies on linux specific stuff that is difficult to implement notably cgroups to isolate the deamons it starts so it knows when they stopped regardless of their pid just assume you can't use systemd on anything else than linux ## IRC, OFTC, #debian-hurd, 2013-08-12 huh, Lennert Poettering just mentioned the Hurd in his systmd talk well, in the context of you IPC in Unix sucks and kdbus s/you/how/ QED what did you expect? :) I didn't quite get it, but he seemed to imply the Hurd was a step in the right direction over Unix (which is obvious, but it wasn't obvious he had that opinion) ## IRC, OFTC, #debian-hurd, 2013-08-13 so cgroups seems to be most prominent thing the systemd people think the Hurd lacks azeem: In 2010, I came to the same conclusion, . ;-) heh I don't think of any show-stopper for implementing that -- just someone to do it. azeem: which part of cgroups, like being able to kill a cgroup? it shouldn't be very hard to implement what systemd needs probably also the resource allocation etc. the questions are I guess (i) do the cgroups semantics make sense from our POV and/or do we accept that cgroups is the "standard" now and (ii) should systemd require concrete implementations or just the concept in a more abstract sense being the first non Linux OS that runs systemd would be a nice showcase of Hurds flexibility maybe upstart is less trouble azeem: possibly teythoon: can you just include upstart in your GSOC? kthxbye at least libnih (the library with base utilities and such used by upstart) required a working file monitor (and the current implementation kind of exposes a fd) and certain semantics for waitid libnih/upstart have "just" the issue of being under CLA... pinotree: yeah, true I suggested "startup" as a name for a fork imho there would be no strict need to fork azeem: but upstart is a lot less interesting. last time I used it it wasn't even possible to disable services in a clean way pinotree: is that still so now that Scott works for google? pochu: yeah, since it's a Canonical CLA, not rally something tied to a person (iirc) sure, but scott is the maintainer... shrug nah, scott left upstart AFAIK at least James Hunt gave a talk earlier with Steve Langasek and introduced himself as the upstart maintainer also I heard in the hallway track that the upstart people are somewhat interested in BSD/Hurd support as they see it as a selling point against systemd pochu: it's just like FSF CLA for GNU projects: even if the maintainers/contributors change altogether, copyright assignment is still FSF but their accents were kinda annoying/hard to follow so I didn't follow their talk closesly to see whether they brought it up pinotree: well, it's not azeem: looking at https://code.launchpad.net/libnih, I'm not sure libnih has a maintainer anymore... pinotree: first off, you're not signing over the copyright with their CLA, just giving them the right to relicense pinotree: but more importantaly, the FSF announced in a legally binding way that they will not take things non-free anyway, I'll talk to the upstart guys about libnih ## IRC, OFTC, #debian-hurd, 2013-08-15 btw, I talked to vorlon about upstart and the Hurd so the situation with libnih is that it is basically feature-complete, but still maintained by Scott upstart is leveraging it heavily and Scott was (back in the days) against patches for porting for upstart proper, Steve said he would happily take porting patches ## IRC, freenode, #hurd, 2013-08-26 < youpi> teythoon: I tend to agree with mbanck < youpi> although another thing worth considering would be adding something similar to control groups < youpi> AIUI, it's one of the features that systemd really requires < braunr> uhg, cgroups already < braunr> youpi: where is that discussion ? < youpi> it was a private mail < braunr> oh ok < teythoon> right, so about upstart < teythoon> to be blunt, I do not like upstart, though my experience with it is limited and outdated < braunr> that was quick :) < braunr> i assume this follows your private discussion with youpi and mbank ? < teythoon> I used it on a like three years old ubuntu and back then it couldn't do stufft hat even sysvinit could do < teythoon> there was not much discussion, mbank suggested that I could work on upstart < teythoon> b/c it might be easier to support than systemd < teythoon> which might be very well true, then again what's the benefit of having upstart? I'm really curious, I should perhaps read up on its features < pinotree> event-based, etc < youpi> it is also about avoiding being pushed out just because we don't support it? < teythoon> yes, but otoh systemd can do amazing things, the featurelist of upstart reads rather mondane in comparison < youpi> I don't really have an opinion over either, apart from portability of the code < braunr> teythoon: the system requirements for systemd would take much time to implement in comparison to what we already have < braunr> i still have maksym's work on last year gsoc on my list < braunr> waiting to push in the various libpager related patches first < teythoon> so you guys think it's worthwile to port upstart? < braunr> no idea < braunr> teythoon: on another subject < azeem_> teythoon: I like systemd more, but the hallway track at Debconf seemed to imply most people like Upstart better except for the CLA < azeem_> which I totally forgot to address < youpi> CLA ? < azeem_> contributor license agreement < braunr> since you've now done very good progress, is your work available in the form of ready-to-test debian packages ? < teythoon> braunr: it is < teythoon> braunr: http://teythoon.cryptobitch.de/gsoc/heap/debian/ < braunr> i remember urls in some of your mails < braunr> ah thanks < braunr> "cryptobitch" hum :) < azeem_> in any case, everbody assumed either Upstart or Systemd are way ahead of systemvinit < braunr> sysvinit is really ancient :) < azeem_> apart from the non-event-driven fundamental issue, a lot of people critized that the failure rate at writing correct init-scripts appears to be too high < azeem_> one of the questions brought up was whether it makes sense to continue to ship/support systemvinit once a switch is made to systemd/upstart for the Linux archs < azeem_> systemvinit scripts might bitrot < azeem_> but anyway, I don't see a switch happen anytime soon < teythoon> well, did upstart gain the capability of disabling a service yet? < azeem_> teythoon: no idea, but apparently: http://askubuntu.com/questions/19320/recommended-way-to-enable-disable-services/20347#20347 < teythoon> azeem_: then there is hope yet ;) < azeem_> the main selling point of Upstart is that it shipped in several LTS releases and is proven technology (and honestly, I don't read a lot of complaints online about it) < azeem_> (I don't agree that SystemD is unproven, but that is what the Upstart guys implied) < teythoon> am I the only one that thinks that upstart is rather unimpressive? * azeem_ doesn't have an opinion on it < azeem> teythoon: http://penta.debconf.org/dc13_schedule/events/1027.en.html has slides and the video < azeem> teythoon: eh, appears the link to the slides is broken, but they are here: http://people.canonical.com/~jhunt/presentations/debconf13/upstart-debconf-2013.pdf < braunr> teythoon: actually, from the presentation, i'd tend to like upstart < braunr> dependency, parallelism and even runlevel compatibility flows naturally from the event based model < braunr> sysv compatibility is a great feature < braunr> it does look simple < braunr> i admit it's "unimpressive" but do we want an overkill init system ? < braunr> teythoon: what makes you not like it ? < azeem> Lennart critized that upstart doesn't generate events, just listens to them < azeem> (which is a feature, not a bug to some) < braunr> azeem: ah yes, that could be a lack < azeem> braunr: http://penta.debconf.org/dc13_schedule/events/983.en.html was the corresponding SystemD talk by Lennart, though he hasn't posted slides yet I think < teythoon> braunr: well, last time I used it it was impossible to cleanly disable a service < teythoon> also ubuntu makes such big claims about software they develop, and when you read up on them it turns out that most of the advertised functionality will be implemented in the near future < teythoon> then they ship software as early as possible only to say later that is has proven itself for so many years < teythoon> and tbh I hate to be the one that helped port upstart to hurd (and maybe kfreebsd as a byproduct) and later debian choses upstart over systemd b/c it is available for all debian kernels < kilobug> teythoon: ubuntu has a tendency to ship software too early when it's not fully mature/stable, but that doesn't say anything about the software itself < pinotree> teythoon: note the same is sometimes done on fedora for young technologies (eg systemd) < azeem> teythoon: heh, fair enough < p2-mate> braunr: I would prefer if my init doesn't use ptrace :P < teythoon> p2-mate: does upstart use ptrace? < p2-mate> teythoon: yes < teythoon> well, then I guess there won't be an upstart for Hurd for some time, no? < kilobug> p2-mate: why does it use ptrace for ? < p2-mate> kilobug: to find out if a daemon forked < kilobug> hum I see < azeem> p2-mate: the question is whether there's a Hurdish way to accomplish the same < p2-mate> http://bazaar.launchpad.net/~upstart-devel/upstart/trunk/view/head:/init/job_process.c < p2-mate> see job_process_trace_new :) < kilobug> azeem: it doesn't seem too complicated to me to have a way to get proc notify upstart of forks < p2-mate> azeem: that's a good question. there is a linuxish way to do that using cgroups < azeem> right, there's a blueprint suggesting cgroups for Upstart here: https://blueprints.launchpad.net/ubuntu/+spec/foundations-q-upstart-overcome-ptrace-limitations < teythoon> yes, someone should create a init system that uses cgroups for tracking child processes >,< < teythoon> kilobug: not sure it is that easy. who enforces that proc_child is used for a new process? isn't it possible to just create a new mach task that has no ties to the parent process? < teythoon> azeem: what do you mean by "upstart does not generate events"? there are "emits X" lines in upstart service descrpitions, surely that generates event X? < azeem> I think the critique is that this (and those upstart-foo-bridges) are bolted on, while SystemD just takes over your systems and "knows" about them first-hand < azeem> but as I said, I'm not the expert on this < teythoon> uh, in order to install upstart one has to remove sysvinit ("yes i am sure...") and it fails to bring up the network on booting the machine < teythoon> also, both systemd and upstart depend on dbus, so no cookie for us unless that is fixed first, right? < pinotree> true < teythoon> well, what do you want me to do for the next four weeks? < youpi> ideally you could make both upstart and systemd work on hurd-i"86 < pinotree> both in 4 weeks? < youpi> so hurd-i386 doesn't become the nasty guy that makes people tend for one or the other < youpi> I said "ideally" < youpi> I don't really have any idea how much work is required by either of the two < youpi> I'd tend to think the important thing to implement is something similar to control groups, so both upstart (which is supposed to use them someday) and systemd can be happy about it < teythoon> looks like upstarts functionality depending on ptrace is not required, but can be enabled on a per service base < teythoon> so a upstart port that just lacks this might be possible < teythoon> youpi: the main feature of cgroups is that a process cannot escape its group, no? i'm not sure how this could be implemented atop of mach in a secure and robust way < teythoon> b/c any process can just create mach tasks < youpi> maybe we need to add a feature in mach itself, yes < teythoon> ok, implementing cgroups sounds fun, I could do that < youpi> azeem: are you ok with that direction? < azeem> well, in general yes; however, AIUI, cgroups is being redesigned upstream, no? < youpi> that's why I said "something like cgroups" < azeem> ah, ok < youpi> we can do something simple enough to avoid design quesetions, and that would still be enough for upstart & systemd < azeem> (http://www.linux.com/news/featured-blogs/200-libby-clark/733595-all-about-the-linux-kernel-cgroups-redesign) btw < braunr> p2-mate: upstart uses ptrace ? < p2-mate> yes < youpi> teythoon: and making a real survey of what needs to be fixed for upstart & systemd < p2-mate> see my link posted earlier < braunr> ah already answered < braunr> grmbl < braunr> it's a simple alternative to cgroups though < braunr> teythoon: dbus isn't a proble < braunr> problem < braunr> it's not that hard to fix < youpi> well, it hasn't been fixed for a long time now :) < braunr> we're being slow, that's all < braunr> and interested by other things < gg0> 12:58 < teythoon> btw, who is this heroxbd fellow and why has he suddenly taken interest in so many debian gsoc projects? < gg0> http://lists.debian.org/debian-hurd/2013/05/msg00133.html < gg0> i notice nobody mentioned openrc < pinotree> he's the debian student working on integrating openrc < gg0> pinotree: no, the student is Bill Wang, Benda as he says is a co-mentor https://wiki.debian.org/SummerOfCode2013/Projects#OpenRC_init_system_in_Debian < pinotree> whatever, it's still the openrc gsoc < azeem> well, they wanted to look at it WRT the Hurd, did they follow-up on this? < gg0> btw wouldn't having openrc on hurd be interesting too? < pinotree> imho not really < gg0> no idea whether Bill is also trying to figure out what to do, probably not < azeem> somebody could ping that thread you mentioned above to see whether they looked at the Hurd and/or need help/advice < gg0> azeem: yeah somebody who could provide such help/advice. like.. you? for instance * gg0 can just paste urls < azeem> they should just follow-up on-list ## IRC, freenode, #hurd, 2013-08-28 anyone knows a user of cgroups that is not systemd? so far I found libcg, that looks like a promising first target to port first, though not surprisingly it is also somewhat linux specific teythoon: OpenRC optionally uses cgroups IIRC. Not mandatory because unlike systemd it actually tries (at all) to be portable. ## IRC, freenode, #hurd, 2013-09-02 braunr: I plan to patch gnumach so that the mach tasks keep a reference to the task that created them and to make that information available braunr: is such a change acceptable? teythoon: what for ? braunr: well, the parent relation is currently only implemented in the Hurd, but w/o this information tracked by the kernel I don't see how I can prevent malicious/misbehaving applications to break out of cgroups also I think this will enable us to fix the issue with tracking which tasks belong to which subhurd in the long term ah cgroups yes cgroups should partly be implemented in the kernel ... teythoon: that doesn't surprise me i mean, i think it's ok the kernel should implement tasks and threads as closely as the hurd (or a unix-like system) needs it braunr: ok, cool braunr: I made some rather small and straight forward changes to gnumach, but it isn't doing what I thought it would do :/ braunr: http://paste.debian.net/33717/ you added a field to task_basic_info thereby breaking the ABI braunr: my small test program says: my task port is 1(pid 13) created by task -527895648; my parent task is 31(pid 1) braunr: no, it is not. I appended a field and these structures are designed to be extendable hm ok although i'm not so sure there are macros defining the info size, depending on what you ask you may as well get garbage have you checked that ? i initialized my struct to zero before calling mach teythoon: can you put some hardcoded value, just to make sure data is correctly exported ? braunr: right, good idea braunr: my task port is 1(pid 13) created by task 3; my parent task is 31(pid 1) -- so yes, hardcoding 3 works ok braunr: also I gathered evidence that the convert_task_to_port thing works, b/c first I did not have the task_reference call just before that so the reference count was lowered (convert... consumes a reference) and the parent task was destroyed braunr: I must admit I'm a little lost. I tried to return a reference to task rather than task->parent_task, but that didn't work either braunr: I feel like I'm missing something here maybe I should get aquainted with the kernel debugger err, the kernel debugger is not accepting any symbol names, even though the binary is not stripped o_O err, neither the kdb nor gdb attached to qemu translates addresses to symbols, gdb at least translates symbols to addresses when setting break points how did anyone ever debug a kernel problem under these conditions? teythoon: i'll have a look at it when i have some time ## IRC, freenode, #hurd, 2013-09-03 :/ I believe the startup_notify interface is ill designed... an translator can defer the system shutdown indefinitely it can that's bad yes the hurd has a general tendency to trust its "no mutual trust required" principle to rely on it a bit too much well, at least it's a privileged operation to request this kind of notification, no? why ? teythoon: it normally is used mostly by privileged servers but i don't think there is any check on the recipient braunr: b/c getting the port to /hurd/init is done via proc_getmsgport teythoon: ? braunr: well, in order to get the notifications one needs the msgport of /hurd/init and getting that requires root privileges teythoon: oh ok then teythoon: what's bad with it then ? braunr: even if those translators are somewhat trusted, they can (and do) contain bugs and stall the shutdown I think this even happened to me once, I think it was the pfinet translator teythoon: how do you want it to behave instead ? braunr: well, /hurd/init notifies the processes sequentially, that seems suboptimal, better to send async notifications to all of them and then to collect all the answers braunr: if one fails to answer within a rather large time frame (say 5 minutes) shutdown anyway i agree with async notifications but i don't agree with the timeout for reference, a (voluntary) timeout of 1 minute is hardcoded in /hurd/init the timeout should be a parameter it's common on large machines to have looong shutdown delays of the notification? the answer means "ok i'm done you can shutdown" well this can take long most often, administrators simply prefer to trust their program is ok and won't take longer than it needs to, even if it's long and not answering at all causes the shutdown / reboot to fail making the system hang i know in a state where it is not easily reached if you do not have access to it but since it only concerns essential servers, it should befine essential servers are expected to behave well it concerns servers that have requested a shutdown notification ok so no essential but system servers essential servers are only exec, proc, / yes the same applies init and auth too, no? yes you expect root not to hang himself I do expect all software to contain bugs yes but you also expect them to provide a minimum level of reliability otherwise you can just throw it all away no, not really well I know, that's my dilemma basically ;) if you don't trust your file system, you make frequent backups if you don't trust your shutdown code, you're ready to pull the plug manually (or set a watchdog or whatever) what i mean is we should NEVER interfere with a program that is actually doing its job just because it seems too long timeouts are almost never the best solution they're used only when necessary e.g. across networks it's much much much worse to interrupt a proper shutdown process because it "seems too long" than just trust it behaves well 99999%%%% of the time in particular because this case deals with proper data flushing, which is an extremely important use case it's hard/theoretically impossible to distinguish between taking long and doing nothing it's impossible agreed => trust if you don't trust, you run real time stuff and you don't flush data on disk ^^ (which makes a lot of computer uses impossible as well) there are only 2 people I trust, and the other one is not /hurd/pfinet if this shutdown procedure is confined to the TCB, it's fine to trust it goes well tcb? trusted computing base http://en.wikipedia.org/wiki/Trusted_computing_base * teythoon shudders "trust" is used way to much these days and I do not like the linux 2.0 ip stack to be part of our TCB basically, on a multiserver system like the hurd, the tcb is every server on the path to getting a service done from a client then make it not request to be notified or make two classes of notifications because unprivileged file systems should be notified too indeed by the way, we should have a hurdish libnotify or something for this kind of notifications but in any case, it should really be policy we should ... :) ^^ ## IRC, freenode, #hurd, 2013-09-04 braunr: btw, I now believe that no server that requested shutdown notifications can stall the shutdown for more than 1 minute *unless* its message queue is full so any fs should better sync within that timeframe where is this 1 min defined ? init/init.c search for 60000 ew did I just find the fs corruption bug everyone was looking for? no what corruption bug ? not sure, I thought there was still some issues left with unclean filesystems every now and then *causing yes but we know the reasons ah involving some of the funniest names i've seen in computer terminology : writeback causing "message floods", which in turn create "thread storms" in the servers receiving them ^^ it's usually the other way around, storms causing floods >,, teythoon: :) let's say it's a bottom-up approach then the fix is easy, compile mach with -DMIGRATING_THREADS :) teythoon: what ? well, that would solve the flood/storm issue, no? no the real solution is proper throttling which can stem from synchronous rpc (which is the real property we want from migrating threads) but the mach writeback interface is async :p ## IRC, freenode, #hurd, 2013-09-05 teythoon: oh right, forgot about your port issue don't worry, I figured by now that this must be a pointer and I'm probably missing some magic that transforms this into a name for the receiver (though I "found" this function by looking at the mig transformation for ports) i was wondering why you called the convert function manually instead of simply returning the task and let mig do the magic b/c then I would have to add another ipc call, no? let me see the basic info call again my problem with this code is that it doesn't take into account the ipc space of the current task which means you probably really return the ipc port the internal kernel address of the struct indeed, ipc_port_t convert_task_to_port(task) i'd personally make a new rpc instead of adding it to basic info basic info doesn't create rights what you want to achieve does you may want to make it a special port i.e. a port created at task creation time y? it also means you need to handle task destruction and reparent yes, I thought about that see http://www.gnu.org/software/hurd/gnumach-doc/Task-Special-Ports.html#Task-Special-Ports for now you may simply turn the right into a dead name when the parent dies although adding a call and letting mig do it is simpler mig handles reference counting, users just need to task_deallocate once done o_O mig does reference counting of port rights? mig/mach_msg is there anything it *doesn't* do? i told you, it's a very complicated messaging interface coffee ? fast ? ^^ mig knows about copy_send/move_send/etc... so even if it doesn't do reference counting explicitely, it does take care of that true in addition, the magic conversions are intended to both translate names into actual structs, and add a temporary reference at the same time teythoon: everything clear now ? :) braunr: no, especially not why you suggested to create a special port. but this will have to wait for tomorrow ;) ## IRC, OFTC, #debian-hurd, 2013-09-06 teythoon: hi there so I've been following your blog entries about cgroups on hurd... very impressive :) but I think there's a misunderstanding about upstart and cgroups... your "conjecture" in https://teythoon.cryptobitch.de/posts/what-will-i-do-next-cgroupfs-o/ is incorrect cgroups does not give us the interfaces that upstart uses to define service readiness; adding support for cgroups is interesting to upstart for purposes of resource partitioning, but there's no way to replace ptrace with cgroups for what we're doing vorlon: hi and thanks for the fish :) vorlon: what is it exactly that upstart is doing with ptrace then? .,oO( your nick makes me suspicious for some reason... ;) service readiness, what does that mean exactly? teythoon: so upstart uses ptrace primarily for determining service readiness. The idea is that traditionally, you know an init script is "done" when it returns control to the parent process, which happens when the service process has backgrounded/daemonized; this happens when the parent process exits in practice, however, many daemons do this badly so upstart tries to compensate, by not just detecting that the parent process has exited, but that the subprocess has exited (for the case where the upstart job declares 'expect daemon') cgroups, TTBOMK, will let you ask "what processes are part of this group" and possibly even "what process is the leader for this group", but doesn't really give you a way to detect "the lead process for this group has changed twice" now, it's *better* in an upstart/systemd world for services to *not* daemonize and instead stay running in the foreground, but then there's the question of how you know the service is "ready" before moving on to starting other services that depend on it systemd's answer to this is socket-based activation, which we don't really endorse for upstart for a variety of reasons hm, okay so upstart does this only if expect daemon is declared in the service description? (in part because I've seen security issues when playing with the systemd implementation on Fedora, which Lennart assures me are corner-cases specific to cups, but I haven't had a chance to test yet whether he's right) and it is not used to track children, but only to observe the daemonizing process? yes and it then detaches from the processes? yes once it knows the service is "ready", upstart doesn't care about tracking it; it'll receive SIGCHLD when the lead process dies, and that's all it needs to know ok, so I misunderstood the purpose of the ptracing, thanks for clarifying this my pleasure :) I realize that doesn't really help with the problem of hurd not having ptrace no, but thanks anyway fwiw, the alternative upstart recommends for detecting service readiness is for the process to raise SIGSTOP when it's ready doesn't require ptracing, doesn't require socket-based activation definitions; does require the service to run in a different mode than usual where it will raise the signal at the correct time right, but that requires patching it, same as the socket activation stuff of systemd (this is upstart's 'expect stop') yes though at DebConf, there were some evil ideas floating around about doing this with an LD_PRELOAD or similar ;) (overriding 'daemonize') er, 'daemon()' ^^ and hey, what's suspicious about my /nick? vorlons are always trustworthy ;) sure they are but could this functionality be reasonably #ifdef'ed out for a proof of concept port? hmm, you would need to implement some kind of replacement... if you added cgroups support to upstart as an alternative that could work i.e., you would need upstart to know when the service has exited; if you aren't using ptrace, you don't know the "lead pid" to watch for, so you need some other mechanism --> cgroups and even then, what do you do for a service like openssh, which explicitly wants to leave child processes behind when it restarts? right... oh, I was hoping you knew the answer to this question ;) Since AFAICS, openssh has no native support for cgroups >,< I don't, but I'll think about what you've said... gotta go, catch what's left of the summer ;) fwiw I consider fork/exec/the whole daemonizing stuff fubar... see you around :) later :) ## IRC, OFTC, #debian-hurd, 2013-09-07 vorlon: I thought about upstarts use of ptrace for observing the daemonizing process and getting hold of the child vorlon: what if cgroup(f)s would guarantee that the order of processes listed in x/tasks is the same they were added in? vorlon: that way, the first process in the list would be the daemonized child after the original process died, no? teythoon: that doesn't tell you how many times the "lead" process has changed, however you need synchronous notifications of the forks in order to know that, which currently we only get via ptrace ## IRC, OFTC, #debian-hurd, 2013-09-08 vorlon: ok, but why do the notifications have to be synchronous? does that imply that the processes need to be stopped until upstart does something? teythoon: well, s/synchronous/reliable/ you're right that it doesn't need to be synchronous; but it can't just be upstart polling the status of the cgroup because processes may have come and gone in the meantime vorlon: ok, cool, b/c the notifications of process changes I'm hoping to introduce into the proc server for my cgroupfs do carry exactly this kind of information cool are you discussing an API for this with the Linux cgroups maintainers? otoh it would be somewhat "interesting" to get upstart to use this b/c of the way the mach message handling is usually implemented :) no, I meant in order for me to be able to implement cgroupfs I had to create these kind of notifications, it's not an addition to the cgroups api is upstart multithreaded? no threads are evil ;) ^^ I mostly agree it uses a very nice event loop, leveraging signalfd among other things uh oh, signalfd sounds rather Linuxish it is I think xnox mentioned when he was investigating it that kfreebsd now also supports it but yeah, AFAIK it's not POSIX it isn't, yes but it darn well should be :) it's the best improvement to signal handling in a long time systemd also uses signalfd umm, it seems I was wrong about Hurd not having ptrace, the wiki suggests that we do have it FSVO "have" ^^ vorlon: teythoon: so ok kFreeBSD/FreeBSD ideally I'd be using EVFILT_PROC from kevent which allows to receive events & track: exit, fork, exec, track (follow across fork) upstart also uses waitid() so a ptrace/waitid should be sufficient to track processes, if Hurd has them. ## IRC, freenode, #hurd, 2013-09-09 teythoon: yes, the shutdown notifications do stall the process but no more than a minute, or so teythoon: btw, did you end up understanding the odd thing in fshelp_start_translator_long? I haven't had the time to have a look youpi: what odd thing? the thing about being implemented by hand instead of using the mig stub? the thing about the port being passed twice XXX this looks wrong to me, please have a look in the mach_port_request_notification call ah, that was alright, yes ok so I can drop it from my TODO :) this is done on the control port so that a translator is notified if the "parent" translator dies was that in fshelp_start_translator_long though? I thought that was somewhere else that's what the patch file says +++ b/libfshelp/start-translator-long.c @@ -293,6 +293,7 @@ fshelp_start_translator_long (fshelp_open_fn_t underlying_open_fn, + /* XXX this looks wrong to me, bootstrap is used twice as argument... */ bootstrap, MACH_NOTIFY_NO_SENDERS, 0, right I remember that when I got a better grip of the idea of notifications I figured that this was indeed okay I'll have a quick look though ok ah, I remember, this notifies the parent translator if the child dies, right and it is a NO_SENDERS notification, so it is perfectly valid to use the same port twice, as we only hold a receive right ## IRC, freenode, #hurd, 2013-09-10 braunr: are pthreads mapped 1:1 to mach threads? teythoon: yes I'm reading the Linux cgroups "documentation" and it talks about tasks (Linux threads) and thread group IDs (Linux processes) and I'm wondering how to map this accurately onto Hurd concepts... apparently on Linux there are PIDs/TIDs that can be used more or less interchangeably from userspace applications the Linux kernel however knows only PIDs, and each thread has its own, and those threads belonging to the same (userspace) PID have the same thread group id aiui on Mach threads belong to a Mach task, and there is no global unique identifier exposed for threads, right? braunr: ^ teythoon: There is its thread port, which in combination with its task port should make it unique? (I might be missing context.) Eh, no. The task port's name will only locally be unique. * tschwinge confused himself. tschwinge, braunr: well, the proc server could of course create TIDs for threads the same way it creates PIDs for tasks, but that should probably wait until this is really needed for the most part, the tasks and cgroup.procs files contain the same information on Linux, and not differentiating between the two just means that cgroupfs is not able to put threads into cgroups, just processes that might be enough for now ## IRC, freenode, #hurd, 2013-09-11 ugh, some of the half-backed Linux interfaces will be a real pain in the ass to support they do stuff like write(2)ing file descriptors encoded as decimal numbers for notifications :-/ teythoon: for cgroup ? braunr: yes, they have this eventfd based notification mechanism