Re: wireless notes / pre d80211 merge
On Wed, 2006-11-15 at 01:11 +0100, Jiri Benc wrote: I wouldn't say useless. It's actually a hack (and you yourself described in (7) why it is currently necessary). We'll need to live with it or cripple the stack to support only very basic features or rewrite the Linux networking core. Choose your own favorite solution :-) I'd be fine with living with what you think of as a hack for a while if the medium- to long-term plan is to rewrite the networking core to get rid of it. I'm just not sure it makes sense. During the tx handlers phase that copy of skb-cb is extended quite a lot with other information determined in the tx handlers. The result is a structure that doesn't fit into cb anymore. This is a reason for not using cb to pass tx information to drivers. Actually, no, it isn't :) The part that is passed to drivers does fit, only the internal stuff doesn't. Straying a bit from the discussion of frames and similar, let me describe the wiphy concept we currently have. Currently, in sysfs we have class/ieee80211/phy%d/ and below that a wealth of information not only about various hardware related things but also, for example, a list of all stations associated to any virtual access points intermixed with those 'stations' that we are associated to on any virtual interface. Also, we here find 'add_iface' and 'remove_iface', knobs to create and destroy virtual interfaces. The second wiphy concept is currently present in cfg80211 which currently requires this concept in the userspace interface and should effectively replace the 'add_iface' and 'remove_iface' hooks and make them more generically available for non-d80211 drivers. I was thinking of ipw2200 when I wrote it which allows adding a monitor device (currently through some config option I think). Not a big problem to combine these two wiphys into just one. Right, that's no biggie. I was just trying to describe what we currently have an forgot to mention it. Please note that master interface has been always considered as a hack. Of course, this perception can be changed if it's desirable. Has it? Simon seems to disagree ;) The master netdev and wiphy create two orthogonal interfaces to userspace that nonetheless pretty much represent the same thing---the underlying hardware. Yup. You just say it like that. Aren't you unhappy about that at all? There is one thing you haven't mentioned and which was probably the key reason for not believing this concept was wrong: we want to make the transition to the new stack as smooth to the users as possible. Users are not used to use the master interface. But since we're going to have a new set of userspace tools anyway, this point is no longer valid. No, wait! We're transitioning from something that only supports one interface to something that supports many virtual ones. As long as we can represent the semantics of the previous single one as the default virtual one, we're fine. Which is actually very possible and cfg80211's WE compat code tries to show that. I don't think the master interface matters here at all. It's just an additional netdev that users previously didn't have, but so what? If this is your biggest problem with d80211 you're really happy :-) Try to fix some locking issue ;-) Let me qualify to externally visible problems :) I'm not too concerned about the internal stuff. That can be cleaned up with some effort, but the externally visible stuff can't actually just be cleaned up without thought and a plan. A full conversion to 802.11 protocol should do much more things and is not possible until we rewrite bridging. You converted the master interface only. That's not what I would call converting d80211 to a 802.11 protocol. I've said this before but let me repeat. There are two ends to d80211 top:virtual interfaces, most likely 802.3 for at least a while if not forever bottom: communication with hardware, qdiscs, etc. I've never wanted to change the top part (so far anyway :) ). It's orthogonal. And whether d80211 behaves as an 802.11 protocol is something that's visible only in the RX path really, struct packet_type and associated things. This seems quite elegant, but there are a couple of problems with it: - skb-cb is sort of abused, and might be too small in the future. If This is a blocker issue for me. it becomes too small, we could put a pointer into skb-cb instead and do lifetime management with an skb desctructor. Not very effective but will work. Not really less effective than copying it around all the time as we do now and then kmalloc()ing it in some circumstances. johannes - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
On Tue, 14 Nov 2006 18:10:50 -0800, Simon Barber wrote: I disagree that the master device is a hack It's a clever hack but still a hack. The Linux network interfaces wasn't designed for the sort of things we do with master interface. Actually, the networking core doesn't support the concept of wiphys at all. Yes, Jouni found a really clever way around this. But the most correct solution is different. In particular: - The operations that make sense for user to perform on wiphy/master interface are different than the ones on virtual interfaces. It isn't this way now. - Why should master interface appear in ifconfig and similar tools the same way as virtual interfaces? If you want to know how users are confused by this, just search some forums. - Does attaching of qdiscs to virtual interfaces make sense? - Etc. To me, the master interface in its current shape is a nice workaround of kernel limitations, but still not a clean solution. I also disagree that we should use 802.11 format frames anywhere but internally inside the 802.11 stack. The 802.11 specification does not use 802.11 format frames to communicate with the upper layers - it uses almost exactly the same interface as 802.3 ethernet does. This is a 2 address interface. I believe that using the standard 2 address format to talk with upper layers matches well with the spec and is the right way to do things. This is a different thing. See the difference between SOCK_RAW and SOCK_DGRAM. The interface you are talking about is SOCK_DGRAM. Except it supports only one address. The correct solution would be extending sockaddr_ll (that's not possible, I know) or introduce a new SOCK_SOMETHING type (not possible either, at least in a short term). If you put 802.11 frame format directly into the L3 protocols then you make all these protocols depend on the MAC - since they will now implement part of the MAC inside the L3 protocol. I don't think this is the right thing to do. I believe that the mapping of 3 and 4 address frames to a particular virtual 2 address port is the right way to do this mapping. For some kind of applications SOCK_RAW on 802.11 interfaces makes sense. (Actually, that's not so simple as they need to specify other things like tx rate but that's an another story.) It is normal to have a single interface to represent the physical hardware network interface. Except that all other hardware doesn't need things that we need. They need just one virtual interface - so their master and virtual interface is merged. This is net_device. We need to split it into two things. This is exactly the pattern that many other physical network devices use. Things like sniffing should go on on this physical interface - and the changes that johannes proposes are exactly the right things to enable this. I would go further - and perhaps move some of the meta-data that is in the skb-cb into a d80211 specific hardware header. This would allow sniffers to directly attach to the master device and both send and receive frames complete with the meta data. It would also reduce the amount of cb space we need. Virtual devices could be created in order to use sniffers that use a different hardware header format (with a small performance penalty when using those). This seems as a really bad solution to me. I fully agree with Johannes regarding this. Thanks, Jiri -- Jiri Benc SUSE Labs - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: wireless notes / pre d80211 merge
I would go further - and perhaps move some of the meta-data that is in the skb-cb into a d80211 specific hardware header. This would allow sniffers to directly attach to the master device and both send and receive frames complete with the meta data. It would also reduce the amount of cb space we need. Virtual devices could be created in order to use sniffers that use a different hardware header format (with a small performance penalty when using those). I'm not sure this is a good idea, it locks us in to some format because user-space uses it and we'd need to serialise to that format to be extensible. On the other hand, we could fix some part of the structure to be user-space visible, make it a real struct that just lives before the 802.11 header and don't serialise like it would be necessary with something that is extensible. On RX, we could do the same. For TX, this would allow applications to control whatever we put into that struct (I would not, for example, allow tx status notifications to ever go over a netdev as we do now), while for RX it would allow apps to see almost everything. It might complicate code a bit because different things would come from different places (some things from a special header and some from skb-cb), but I don't think it would be bad. Other than this, I agree with you. johannes - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
On Wed, 15 Nov 2006 10:16:18 +0100, Johannes Berg wrote: During the tx handlers phase that copy of skb-cb is extended quite a lot with other information determined in the tx handlers. The result is a structure that doesn't fit into cb anymore. This is a reason for not using cb to pass tx information to drivers. Actually, no, it isn't :) The part that is passed to drivers does fit, only the internal stuff doesn't. Sorry, I was wrong here. I rechecked it now and starting from the last diet (made by me long time ago, grr) it fits. Please note that master interface has been always considered as a hack. Of course, this perception can be changed if it's desirable. Has it? Simon seems to disagree ;) And I disagree with Simon :-) The master netdev and wiphy create two orthogonal interfaces to userspace that nonetheless pretty much represent the same thing---the underlying hardware. Yup. You just say it like that. Aren't you unhappy about that at all? I wasn't in times when there was no cfg80211. But now... yes, you're right. The sysfs ieee80211 class exports just some interesting informations (we already agreed that add_interface and remove_interface would go away). Feel free to move it wherever you think is appropriate. I don't think the master interface matters here at all. It's just an additional netdev that users previously didn't have, but so what? As I said, my pre-cfg80211 arguments are not valid now. Let me qualify to externally visible problems :) Okay :-) I've never wanted to change the top part (so far anyway :) ). It's orthogonal. And whether d80211 behaves as an 802.11 protocol is something that's visible only in the RX path really, struct packet_type and associated things. I just said it's a confusing term, nothing against the idea. it becomes too small, we could put a pointer into skb-cb instead and do lifetime management with an skb desctructor. Not very effective but will work. Not really less effective than copying it around all the time as we do now and then kmalloc()ing it in some circumstances. That's true. Thanks, Jiri -- Jiri Benc SUSE Labs - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
On Wed, 2006-11-15 at 10:43 +0100, Jiri Benc wrote: In particular: - The operations that make sense for user to perform on wiphy/master interface are different than the ones on virtual interfaces. It isn't this way now. Which particular operations do you have in mind? Granted, you won't ever be able to specify the master device as the default route for IP, but hey. I'd almost bet there are other devices that you can't do this with. - Why should master interface appear in ifconfig and similar tools the same way as virtual interfaces? If you want to know how users are confused by this, just search some forums. Because it manages the qdiscs and frames actually show up there. Even now, you can there see what you're transmitting :) - Does attaching of qdiscs to virtual interfaces make sense? Yes, I do think so. Why not? This is a different thing. See the difference between SOCK_RAW and SOCK_DGRAM. The interface you are talking about is SOCK_DGRAM. Except it supports only one address. The correct solution would be extending sockaddr_ll (that's not possible, I know) or introduce a new SOCK_SOMETHING type (not possible either, at least in a short term). I still haven't quite understood this argument. Could you elaborate? Except that all other hardware doesn't need things that we need. They need just one virtual interface - so their master and virtual interface is merged. This is net_device. We need to split it into two things. That's not really true, if you have a 802.1q network then the raw netdev is useless without vlan virtuals above unless you unpack the vlan on the switch giving you a non-802.1q network again. johannes - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
On Wed, 2006-11-15 at 11:05 +0100, Jiri Benc wrote: I wasn't in times when there was no cfg80211. But now... yes, you're right. The sysfs ieee80211 class exports just some interesting informations (we already agreed that add_interface and remove_interface would go away). Feel free to move it wherever you think is appropriate. Even with cfg80211 we have the wiphy concept embedded in there. Not much difference because we still have to do tc on wmasterN and wiconf on wiphyN. So that doesn't really change anything. Now, we could of course drop the wiphy concept from cfg80211 easily and require doing all these things on wmasterN. That's the option I considered in section (8). I don't like it too much, but I think I could live with it. johannes - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
Simon Barber wrote: I disagree that the master device is a hack - I also disagree that we should use 802.11 format frames anywhere but internally inside the 802.11 stack. The 802.11 specification does not use 802.11 format frames to communicate with the upper layers - it uses almost exactly the same interface as 802.3 ethernet does. This is a 2 address interface. I The 802.11 specification doesn't communicate with any layer :) The Linux kernel code in question does that. In Linux it is generally bad form to emulate something (802.3 ethernet, in this case). Overhead increases, performance decreases, and there are inevitably emulation bugs. 802.11 /is not ethernet/, and you are already breaking assumptions by pretending that it is. It is normal to have a single interface to represent the physical hardware network interface. This is exactly the pattern that many other physical network devices use. Things like sniffing should go on on this physical interface - and the changes that johannes proposes are exactly the right things to enable this. Sure... when it behaves like a normal interface. Stuff like TX goes through the interface, but not RX is definitely /not/ normal. Jeff - To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wireless notes / pre d80211 merge
On Tue, 14 Nov 2006 23:19:57 +0100, Johannes Berg wrote: 1. master netdev Currently, we have the 'master' netdev wmasterN which is created as native 802.11 device but is essentially useless. It is exported to userspace but only supports wireless extensions and, depending on what the drivers do, ethtool ops. It isn't really useful for network functionality although outgoing frames can be seen on it. See section (3) for why. I wouldn't say useless. It's actually a hack (and you yourself described in (7) why it is currently necessary). We'll need to live with it or cripple the stack to support only very basic features or rewrite the Linux networking core. Choose your own favorite solution :-) [1] why we didn't make a static inline ieee80211_rx() that calls an exported __ieee80211_rx() until we get rid of the other ieee80211 is beyond me. Would have been good but I guess we can also just convert all the drivers when we change the name again. Yes, it's just temporary and it doesn't matter. 3. skb path during tx This is more complicated. When a frame is created in one of the virtual interfaces, it first goes through through conversion from 802.3 into 802.11, some tx control is added on and the frame is queued to the master netdev. This is why we see outgoing frames in tcpdump. After getting queued to the master netdev, the frame goes through the qdiscs and some more info is tacked on into skb-cb by the 802.11 qdisc. Afterwards, if the frame is not dropped, it shows up in ieee80211_master_start_xmit where skb-cb is copied onto the stack and cleared afterwards. Then, the frame goes through all the tx handlers including fragmentation and encryption and is finally given to the lowlevel driver via the hardware description's tx() call. During the tx handlers phase that copy of skb-cb is extended quite a lot with other information determined in the tx handlers. The result is a structure that doesn't fit into cb anymore. This is a reason for not using cb to pass tx information to drivers. 4. wiphy concept Straying a bit from the discussion of frames and similar, let me describe the wiphy concept we currently have. Currently, in sysfs we have class/ieee80211/phy%d/ and below that a wealth of information not only about various hardware related things but also, for example, a list of all stations associated to any virtual access points intermixed with those 'stations' that we are associated to on any virtual interface. Also, we here find 'add_iface' and 'remove_iface', knobs to create and destroy virtual interfaces. The second wiphy concept is currently present in cfg80211 which currently requires this concept in the userspace interface and should effectively replace the 'add_iface' and 'remove_iface' hooks and make them more generically available for non-d80211 drivers. I was thinking of ipw2200 when I wrote it which allows adding a monitor device (currently through some config option I think). Not a big problem to combine these two wiphys into just one. 5. so it works, what's wrong? Pretty broad question I asked myself here, but let me try to answer it anyway. For one, I think that having the master device in its current form is useless. It sees outgoing frames that are to be sent to the hardware for transmission, and in that way represents the actual underlying hardware. However, it never sees incoming frames, so there again it doesn't represent the hardware. Not seeing incoming frames makes it useless, and even through it sees outgoing frames you cannot send frames to it. Also, if the master netdev is thought of as representing the hardware (which I don't think it fully does), it collides with the notion of the 'wiphy' as described above. Please note that master interface has been always considered as a hack. Of course, this perception can be changed if it's desirable. Personally, I tried to make this interface uninteresting for users as much as possible - so we can tell ordinary users: That's just an annoying internal thing, don't touch it and don't care about it. Of course, advanced users need to care (because of qdiscs). This is not optimal (although I'm not sure there exists an optimal solution here) and I'm not strongly attached to this. The master netdev and wiphy create two orthogonal interfaces to userspace that nonetheless pretty much represent the same thing---the underlying hardware. Yup. As said previously, the master netdev represents the hardware when it comes to qdisc manipulation, but the wiphy represents the hardware when it comes to manipulation of virtual interfaces. I believe that this is fundamentally wrong because they both manipulate operation of the underlying hardware. There is one thing you haven't mentioned and which was probably the key reason for not believing this concept was wrong: we want to make the transition to the new stack as smooth to the users as possible. Users are not used to use the master
RE: wireless notes / pre d80211 merge
Hi Jiri, I disagree that the master device is a hack - I also disagree that we should use 802.11 format frames anywhere but internally inside the 802.11 stack. The 802.11 specification does not use 802.11 format frames to communicate with the upper layers - it uses almost exactly the same interface as 802.3 ethernet does. This is a 2 address interface. I believe that using the standard 2 address format to talk with upper layers matches well with the spec and is the right way to do things. If you put 802.11 frame format directly into the L3 protocols then you make all these protocols depend on the MAC - since they will now implement part of the MAC inside the L3 protocol. I don't think this is the right thing to do. I believe that the mapping of 3 and 4 address frames to a particular virtual 2 address port is the right way to do this mapping. It is normal to have a single interface to represent the physical hardware network interface. This is exactly the pattern that many other physical network devices use. Things like sniffing should go on on this physical interface - and the changes that johannes proposes are exactly the right things to enable this. I would go further - and perhaps move some of the meta-data that is in the skb-cb into a d80211 specific hardware header. This would allow sniffers to directly attach to the master device and both send and receive frames complete with the meta data. It would also reduce the amount of cb space we need. Virtual devices could be created in order to use sniffers that use a different hardware header format (with a small performance penalty when using those). Simon -Original Message- From: Jiri Benc [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 14, 2006 6:11 PM To: Johannes Berg Cc: netdev; Jeff Garzik; John W. Linville; Simon Barber; Michael Buesch; Ivo van Doorn; Michael Wu; Jouni Malinen; Daniel Drake; Hong Liu; Luis R. Rodriguez; James Ketrenos; David Kimdon; Udayan Singh Subject: Re: wireless notes / pre d80211 merge On Tue, 14 Nov 2006 23:19:57 +0100, Johannes Berg wrote: 1. master netdev Currently, we have the 'master' netdev wmasterN which is created as native 802.11 device but is essentially useless. It is exported to userspace but only supports wireless extensions and, depending on what the drivers do, ethtool ops. It isn't really useful for network functionality although outgoing frames can be seen on it. See section (3) for why. I wouldn't say useless. It's actually a hack (and you yourself described in (7) why it is currently necessary). We'll need to live with it or cripple the stack to support only very basic features or rewrite the Linux networking core. Choose your own favorite solution :-) [1] why we didn't make a static inline ieee80211_rx() that calls an exported __ieee80211_rx() until we get rid of the other ieee80211 is beyond me. Would have been good but I guess we can also just convert all the drivers when we change the name again. Yes, it's just temporary and it doesn't matter. 3. skb path during tx This is more complicated. When a frame is created in one of the virtual interfaces, it first goes through through conversion from 802.3 into 802.11, some tx control is added on and the frame is queued to the master netdev. This is why we see outgoing frames in tcpdump. After getting queued to the master netdev, the frame goes through the qdiscs and some more info is tacked on into skb-cb by the 802.11 qdisc. Afterwards, if the frame is not dropped, it shows up in ieee80211_master_start_xmit where skb-cb is copied onto the stack and cleared afterwards. Then, the frame goes through all the tx handlers including fragmentation and encryption and is finally given to the lowlevel driver via the hardware description's tx() call. During the tx handlers phase that copy of skb-cb is extended quite a lot with other information determined in the tx handlers. The result is a structure that doesn't fit into cb anymore. This is a reason for not using cb to pass tx information to drivers. 4. wiphy concept Straying a bit from the discussion of frames and similar, let me describe the wiphy concept we currently have. Currently, in sysfs we have class/ieee80211/phy%d/ and below that a wealth of information not only about various hardware related things but also, for example, a list of all stations associated to any virtual access points intermixed with those 'stations' that we are associated to on any virtual interface. Also, we here find 'add_iface' and 'remove_iface', knobs to create and destroy virtual interfaces. The second wiphy concept is currently present in cfg80211 which currently requires this concept in the userspace interface and should effectively replace the 'add_iface' and 'remove_iface' hooks and make them more generically available for non-d80211 drivers. I was thinking of ipw2200 when I wrote it which allows adding a monitor device (currently
