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diff --git a/open_issues/bpf.mdwn b/open_issues/bpf.mdwn index 73f73093..98b50430 100644 --- a/open_issues/bpf.mdwn +++ b/open_issues/bpf.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2009 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2009, 2012 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 @@ -70,3 +70,373 @@ This is a collection of resources concerning *Berkeley Packet Filter*s. * [[!GNU_Savannah_patch 6622]] -- pfinet uses the BPF filter * [[!GNU_Savannah_patch 6851]] -- fix a bug in BPF + + +# IRC + +## IRC, freenode, #hurd, 2012-01-13 + + <braunr> hm, i think the bpf code needs a complete redesign :p + <braunr> unless it's actually a true hurdish way to do things + <braunr> antrik: i need your help :) + <braunr> antrik: I need advice on the bpf "architecture" + <braunr> the current implementation uses a translator installed at /dev/bpf + <braunr> which means packets from the kernel are copied to that translator + and then to client applications + <braunr> does that seem ok to you ? + <braunr> couldn't the translator be used to set a direct link between the + kernel and the client app ? + <braunr> which approach seems the more Hurdish to you ? (<= this is what I + need your help on) + <pinotree> braunr: so there would be a roundtrip like kernel → bpf + translator → pfinet? + <antrik> braunr: TBH, I don't see why we need a BPF translator at all... + <braunr> antrik: it handles the ioctls + <braunr> pinotree: pfinet isn't involved (it was merely modified to use the + "new" filter format to specify it used the old packet filter, and not + bpf) + <antrik> braunr: do we really need to emulate the ioctl()s? can't we assume + that all packages using BPF will just use libpcap? + <antrik> (and even if we *do* want to emulate ioctl()s, why can't we handle + this is libc?) + <braunr> antrik: that's what i'm wondering actually + <braunr> even if assuming all packages use libpcap, i'd like our bpf + interface to be close to what bsds have, and most importantly, what + libpcap expects from a bpf interface + <antrik> well, why? if we already have a library handling the abstraction, + I don't see much point in complicating the design and use by adding + another layer :-) + <braunr> so you would advise adapting libpcap to include a hurd specific + module ? + <antrik> there are two reasons for adding translators: more robustness or + more flexibility... so far I don't see how a BPF translator would add + either + <braunr> right + <antrik> yes + <braunr> so we'd end up with a bpf-like interface, the same instructions + and format, with different control calls + <antrik> right + <antrik> note that I had more or less the same desicion to make for KGI + (emulate Linux/BSD ioctl()s, or implement a backend in libggi for + handling Hurd-specific RPC; and after much consideration, I decided on + the latter) + + +## IRC, freenode, #hurd, 2012-01-16 + + <braunr> antrik: is there an existing facility to easily give a send right + to the device master port to a task ? + <braunr> another function of the bpf translator is to handle the /dev/bpf + node, and most importantly its permissions + <braunr> so that users which have read/write access to the node have access + to the packet filter + <braunr> i guess the translator could limit itself to that functionality + <braunr> and then provide a device port on which libpcap operates directly + by means of device_{g,s}et_status/device_set_filter + <antrik> braunr: I don't see the point in seperating permissions for filter + from permissions from general network device access... + <antrik> as for device master port, all root tasks can obtain it from proc + IIRC + <braunr> antrik: yes, but how do we allow non-root users to access that + facility ? + <braunr> on a unix like system, it's a matter of changing the permissions + of /dev/bpf + <antrik> with devnode, non-root users can get access to specific device + nodes, including network devices + <braunr> i can't imagine the hurd being less flexible for that + <braunr> ah devnode + <braunr> good + <antrik> so we can for example make /dev/eth0 accessible by users of some + group + <braunr> what's devnode exactly ? + <antrik> it's a very simple translator that implements an FS node that + looks somewhat like a file, but the only operation it supports is + obtaining a pseudo device master port, giving access to a specific Mach + device + <braunr> is it already part of the hurd ? + <braunr> or hurdextras maybe ? + <antrik> it's only in zhengda's branch + <braunr> ah + <antrik> needed for both eth-multipexer and DDE + <braunr> and bpf soon i guess + <antrik> indeed :-) + <braunr> "obtaining a pseudo device master port", i believe you meant a + pseudo device port + <antrik> I must admit that I don't remember exactly whether devnode proxies + device_open(), so clients direct get a port to the device in question, or + whether it implements a pseudo device master port... + <antrik> but definitely not a pseudo device port :-) + <braunr> i'm almost positive it gives the target device port, otherwise i + don't see the point + <braunr> i don't understand the user of the "pseudo" word here either + <braunr> s/user/use/ + <braunr> aiui, devnode should be started as root (or in any way which gives + it the device master port) + <antrik> the point is that the client doesn't need to know the Mach device + name, and also is not bound to actual kernel devices + <braunr> and when started, implement the required permissions before giving + clients a device port to the specific device it was installed for + <braunr> right + <braunr> but it mustn't be a proxy + <antrik> yes, devnode needs access to either the real master device port + (for kernel devices), or one provided by eth-multiplexer or the DDE + network driver + <braunr> well, a very simple proxy for deviceopen + <braunr> ok + <braunr> that seems exactly what i wanted to do + <braunr> we now need to see if we can integrate it separately + <braunr> create a separate branch that works for the current gnumach code, + and merge dde/other specific code later on + <antrik> you mean independent of eth-multiplexer or DDE? yes, it was + generally agreed that devnode is a good idea in any case. I have no idea + why there are no device nodes for network devices on other UNIX + systems... + <braunr> i've been wondering that for years too :) + <antrik> zhengda's branch has a pfinet modified to a) use devnode, and b) + use BPF + <braunr> why bpf ? + <braunr> for more specific filters maybe ? + <antrik> hm... don't remember whether there was any technical reason for + going with BPF; I guess it just seemed more reasonable to invest new work + in BPF rather than obsolete Mach-specific NPF... + <braunr> cspf could be removed altogether, i agree + <antrik> another plus side of his modified pfinet is that it actually sets + an appropriate filter for TCP/IP and the IP in use, rather than just + setting a dummy filter catching app packets (including those irrelevant + to the specific pfinet instance) + <antrik> err... catching all packets + <braunr> that's what i meant by "for more specific filters maybe ?" + <braunr> he was probably more comfortable with the bpf interface to write + his filter rules + <antrik> well, it would probably be doable with NPF too :-) so by itself + it's not a reason for switching to BPF... + <antrik> it's rather the other way around: as it was necessary to implement + filters in eth-multiplexer, and implementing BPF seemed more reasoable, + pfinet had to be changed to use BPF... + <braunr> antrik: where is zhengda's branch btw ? + <antrik> (I guess using proper filters with eth-multiplexer is not strictly + necessary; but it would be a major performance hit not to) + <antrik> it's in incubator.git + <antrik> but it's very messy + <braunr> ok + <antrik> at some point I asked him to provide cleaned up branches, and I'm + pretty sure he said he did, but I totally fail to remember where he + published them :-( + <braunr> hm, i don't like how devnode is "architectured" :/ + <braunr> but it makes things a little more easy to get working i guess + <LarstiQ> antrik: any idea what to grep the logs on for that? + <braunr> ok never mind, devnode is fine + <braunr> exactly what i need + <braunr> i wonder however if it shouldn't be improved to better handle + permissions + <braunr> ok, never mind either, permission handling is fine + <braunr> so what are we waiting for ? :) + <antrik> I remember that there were some issues with permission handling, + but I don't remember whether all were fixed :-( + <antrik> LarstiQ: hm... good question... + <braunr> ah ? + <braunr> hm actually, there could be issues for packet filters, yes + <braunr> i guess we want to allow e.g. read-only opens for capture only + <antrik> braunr: that would have to be handled by the actual BPF + implementation I'd say + <braunr> it should already be the case + <antrik> what's the problem then? + <braunr> but when the actual device_open() is performed, the appropriate + permissions must be provided + <braunr> and checking those is the responsibility of the proxy, devnode in + this case + <antrik> and it doesn't do that? + <braunr> apparently not + <braunr> the only check is against the device name + <braunr> i'll begin playing with that first + <antrik> I vaguely remember that there has been discussion about the + relation of underlying device open mode and devnode open mode... but I + don't remember the outcome. in fact it was probably one of the + discussions I never got around to follow up on... :-( + <antrik> before you begin playing, take a look at the relevant messages in + the ML archive :-) + <antrik> must have been around two years ago + <braunr> ok + <antrik> some thread with me and scolobb (Sergiu Ivanov +- spelling) and + probably zhengda + <antrik> there might also be some outstanding patch(es) from scolobb, not + sure + + +## IRC, freenode, #hurd, 2012-01-17 + + <braunr> antrik: i think i found the thread you mentioned about devnode + <braunr> neither sergiu nor zhengda considered the use of a read-only + device for packet filtering + <braunr> leading to assumptions such as "only receiving packets + <braunr> is not terribly useful, in view of the fact that you have to at + least + <braunr> request them, which implies *sending* packets :-) + <braunr> " + <braunr> IMO, devnode should definitely check its node permissions to build + the device open flags + <braunr> good news is that it doesn't depend on anything specific to other + incubator projects + <braunr> making it almost readily mergeable in the hurd + <braunr> i'm not sure devnode is an appropriate name though + <braunr> maybe something like device, or devproxy + <braunr> proxy-devopen maybe + <antrik> braunr: well, I don't remember the details of the disucssion; but + as I mentioned in some mail, I did actually want to write a followup, + just didn't get around to it... so I was definitely not in agreement with + some of the statements made by others. I just don't remember on which + point :-) + <antrik> which thread was it? + <antrik> anyways, this should in no way be specific to network + devices... the idea is simply that if the client has only read + permissions on the device node, it should only get to open the underlying + device for read. it's up to the kernel to handle the read-only status for + the device once it's opened + <antrik> as for the naming, the idea is that devnode simply makes Mach + devices accessible through FS nodes... so the name seemed appropriate + <antrik> you may be right though that just "device" might be more + straightforward... I don't agree on the other variants + <braunr> antrik: + http://lists.gnu.org/archive/html/bug-hurd/2009-12/msg00155.html + <braunr> antrik: i agree with the general idea behind permission handling, + i was just referring to their thoughts about it, which probably led to + the hard coded READ | WRITE flags + <antrik> braunr: unfortunately, I don't remember the context of the + discussion... would take me a while to get into this again :-( + <antrik> the discussion seems to be about eth-multiplexer as much as about + devnode (if not more), and I don't remember the exact interaction + + +## IRC, freenode, #hurd, 2012-01-18 + + <braunr> so, does anyone have an objection to getting devnode into the hurd + and calling it something else like e.g. device ? + <youpi> braunr: it's Zhengda's work, right? + <braunr> yes + <youpi> I'm completely for it, it just perhaps needs some cleanup + <braunr> i have a few changes to add to what already exists + <braunr> ok + <braunr> well i'm assigning myself to the task + <antrik> braunr: I'm still not convinced just "device" is preferable + <antrik> perhaps machdevice ;-) + <antrik> but otherwise, I'd LOVE to see it in :-) + <braunr> i don't know .. what if the device is actually eth-multiplexer or + a dde one ? + <braunr> it's not really "mach", is it ? + <braunr> or do we only refer to the interface ? + <youpi> that translator is only for mach devices + <braunr> so you consider dde devices as being mach devices too ? + <braunr> it's a simple proxy for device_open really + <youpi> will these devices use that translator? + <youpi> ah + <youpi> I thought it was using a mach-specific RPC + <braunr> so we can consider whatever we want + <antrik> braunr: yes, the translator is for Mach device interface only. it + might be provided by other servers, but it's still Mach devices + <youpi> then drop the mach, yes + <braunr> i'd tend to agree with antrik + <youpi> antrik: I'd say the device interface is part of the hur dinterfaces + <braunr> then machdev :p + <braunr> no, it's really part of the mach interface + <youpi> it's part of the mach interface, yes + <youpi> but also of the Hurd, no? + <antrik> DDE network servers also use the Mach device interface + <braunr> no + <youpi> can't we say it's part of it? + <youpi> I mean + <youpi> even if we change the kernel + <braunr> dde is the only thing that implements it besides the kernel that i + know of + <youpi> we will probably want to keep the same interface + <braunr> yes but that's a mach thing + <youpi> what we have now is not necessarily a reason + <antrik> as for other DDE drivers, I for my part believe they should export + proper Hurd (UNIX) device nodes directly... but for some reason zhengda + insisted on implementing it as Mach devices too :-( + <braunr> antrik: i agree with you on that too + <braunr> i was a bit surprised to see the same interface was reused + <braunr> youpi: we can, we just have to agree on what we'll do + <braunr> what do you mean by "even if we change the kernel" ? + <antrik> the problem with "machdev" is that it might suggest the translator + actually implements the device... not sure whether this would cause + serious confusion + <antrik> "devopen" might be another option + <antrik> or "machdevopen" to be entirely verbose ;-) + <braunr> an option i suggested earlier which you disagreed on :p + <braunr> but devopen is the one i'd choose + <antrik> youpi: as I already mentioned in the libburn thread, I don't + actually think the Mach device interface is very nice; IMHO we should get + rid of it as soon as we can, rather than port it to other + architectures... + <antrik> but even *if* we decided to reuse it after all, it would still be + the Mach device interface :-) + <braunr> actually, zheng da already suggested that name a long time ago + <braunr> http://lists.gnu.org/archive/html/bug-hurd/2008-08/msg00005.html + <braunr> no actually antrik did eh + <braunr> ok let's use devopen + <antrik> braunr: you suggested proxy-devopen, which I didn't like because + of the "proxy" part :-) + <braunr> not only, but i don't have the logs any more :p + <antrik> oh, I already suggested devopen once? didn't expect myself to be + that consistent... ;-) + <antrik> braunr: you suggested device, devproxy or proxy-devopen + <braunr> ah, ok + <braunr> devopen is better + <antrik> I wonder whether it's more important for clarity to have "mach" in + there or "open"... or whether it's really too unweildy to have both + + +## IRC, freenode, #hurd, 2012-01-21 + + <braunr> oh btw, i made devopen run today, it shouldn't be hard getting it + in properly + <braunr> patching libpcap will be somewhat trickier + <braunr> i don't even really need it, but it allows having user access to + mach devices, which is nice for the libpcap patch and tcpdump tests + <braunr> permission checking is actually its only purpose + <braunr> well, no, not really, it also allows opening devices implemented + by user space servers transparently + + +## IRC, freenode, #hurd, 2012-01-27 + + <braunr> hmm, bpf needs more work :( + <braunr> or we can use the userspace bpf filter in libpcap, so that it + works with both gnumach and dde drivers + <antrik> braunr: there is a userspace BPF implementation in libpcap? I'm + surprised that zhengda didn't notice it, and ported the one from gnumach + instead... + <antrik> what is missing in the kernel implementation? + <braunr> antrik: filling the bpf header + <braunr> frankly, i'm not sure we want to bother with the kernel + implementation + <braunr> i'd like it to work with both gnumach and dde drivers + <braunr> and in the long run, we'll be using userspace drivers anyway + <braunr> the bpf header was one of the things the defunct translator did + <braunr> which involved ugly memcpy()s :p + <antrik> braunr: well, if you want to get rid of the kernel implementation, + basically you would have to take up eth-multiplexer and get it into + mainline + <antrik> (and make sure it's used by default in Debian) + <antrik> I frankly believe it's the better design anyways... but quite a + major change :-) + <braunr> not that major to me + <braunr> in the meantime i'll use the libpcap embedded implementation + <braunr> we'll have something useful faster, with minimum work when + eth-multiplexer is available + <antrik> eth-multiplexer is ready for use, it just needs to go upstream + <antrik> though it's probably desirable to switch it to the BPF + implementation from libpcap + <braunr> using the libpcap implementation in libpcap and in eth-multiplexer + are two different things + <braunr> the latter is preferrable + <braunr> (and yes, by available, i meant upstream ofc) + <antrik> eth-mulitplexer is already using libpcap anyways (for compiling + the filters); I'm sure zhengda just didn't realize it has an actual BPF + implementation too... + <braunr> we want the filter implementation as close to the packet source as + possible + <antrik> I have been using eth-multiplexer for at least two years now + <braunr> hm, there is a "snoop" source type, using raw sockets + <braunr> too far from the packet source, but i'll try it anyway + <braunr> hm wrong, snoop was the solaris packet filter fyi |