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• Stop duplicate icmp echo replies when bridging to a dummy interface?

  - by mbrownnyc

  I recently configured a bridge br0 with members as eth0 (real if) and dummy0 (dummy.ko if). When I ping this machine, I receive duplicate replies as: # ping SERVERA PING SERVERA.domain.local (192.168.100.115) 56(84) bytes of data. 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=114 ms (DUP!) 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms (DUP!) Using tcpdump on SERVERA, I was able to see icmp echo replies being sent from eth0 and br0 itself as follows (oddly two echo request packets arrive "from" my Windows box myhost): 23:19:05.324192 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324212 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324217 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324221 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324264 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324272 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 It's worth noting, testing reveals that hosts on the same physical switch do not see DUP icmp echo responses (a host on the same VLAN on another switch does see a dup icmp echo response). I've read that this could be due to the ARP table of a switch, but I can't find any info directly related to bridges, just bonds. I have a feeling my problem lay in the stack on linux, not the switch, but am opened to any suggestions. The system is running centos6/el6 kernel 2.6.32-71.29.1.el6.i686. How do I stop ICMP echo replies from being sent in duplicate when dealing with a bridge interface/bridged interfaces? Thanks, Matt [edit] Quick note: It was recommended in #linux to: [08:53] == mbrownnyc [gateway/web/freenode/] has joined ##linux [08:57] <lkeijser> mbrownnyc: what happens if you set arp_ignore to 1 for the dummy interface? [08:59] <lkeijser> also set arp_announce to 2 for that interface [09:24] <mbrownnyc> lkeijser: I set arp_annouce to 2, arp_ignore to 2 in /etc/sysctl.conf and rebooted the machine... verifying that the bits are set after boot... the problem is still present I did this and came up empty. Same dup problem. I will be moving away from including the dummy interface in the bridge as: [09:31] == mbrownnyc [gateway/web/freenode/] has joined #Netfilter [09:31] <mbrownnyc> Hello all... I'm wondering, is it correct that even with an interface in PROMISC that the kernel will drop /some/ packets before they reach applications? [09:31] <whaffle> What would you make think so? [09:32] <mbrownnyc> I ask because I am receiving ICMP echo replies after configuring a bridge with a dummy interface in order for ipt_netflow to see all packets, only as reported in it's documentation: http://ipt-netflow.git.sourceforge.net/git/gitweb.cgi?p=ipt-netflow/ipt-netflow;a=blob;f=README.promisc [09:32] <mbrownnyc> but I do not know if PROMISC will do the same job [09:33] <mbrownnyc> I was referred here from #linux. any assistance is appreciated [09:33] <whaffle> The following conditions need to be met: PROMISC is enabled (bridges and applications like tcpdump will do this automatically, otherwise they won't function). [09:34] <whaffle> If an interface is part of a bridge, then all packets that enter the bridge should already be visible in the raw table. [09:35] <mbrownnyc> thanks whaffle PROMISC must be set manually for ipt_netflow to function, but [09:36] <whaffle> promisc does not need to be set manually, because the bridge will do it for you. [09:36] <whaffle> When you do not have a bridge, you can easily create one, thereby rendering any kernel patches moot. [09:36] <mbrownnyc> whaffle: I speak without the bridge [09:36] <whaffle> It is perfectly valid to have a "half-bridge" with only a single interface in it. [09:36] <mbrownnyc> whaffle: I am unfamiliar with the raw table, does this mean that PROMISC allows the raw table to be populated with packets the same as if the interface was part of a bridge? [09:37] <whaffle> Promisc mode will cause packets with {a dst MAC address that does not equal the interface's MAC address} to be delivered from the NIC into the kernel nevertheless. [09:37] <mbrownnyc> whaffle: I suppose I mean to clearly ask: what benefit would creating a bridge have over setting an interface PROMISC? [09:38] <mbrownnyc> whaffle: from your last answer I feel that the answer to my question is "none," is this correct? [09:39] <whaffle> Furthermore, the linux kernel itself has a check for {packets with a non-local MAC address}, so that packets that will not enter a bridge will be discarded as well, even in the face of PROMISC. [09:46] <mbrownnyc> whaffle: so, this last bit of information is quite clearly why I would need and want a bridge in my situation [09:46] <mbrownnyc> okay, the ICMP echo reply duplicate issue is likely out of the realm of this channel, but I sincerely appreciate the info on the kernels inner-workings [09:52] <whaffle> mbrownnyc: either the kernel patch, or a bridge with an interface. Since the latter is quicker, yes [09:54] <mbrownnyc> thanks whaffle [edit2] After removing the bridge, and removing the dummy kernel module, I only had a single interface chilling out, lonely. I still received duplicate icmp echo replies... in fact I received a random amount: http://pastebin.com/2LNs0GM8 The same thing doesn't happen on a few other hosts on the same switch, so it has to do with the linux box itself. I'll likely end up rebuilding it next week. Then... you know... this same thing will occur again. [edit3] Guess what? I rebuilt the box, and I'm still receiving duplicate ICMP echo replies. Must be the network infrastructure, although the ARP tables do not contain multiple entries. [edit4] How ridiculous. The machine was a network probe, so I was (ingress and egress) mirroring an uplink port to a node that was the NIC. So, the flow (must have) gone like this: ICMP echo request comes in through the mirrored uplink port. (the real) ICMP echo request is received by the NIC (the mirrored) ICMP echo request is received by the NIC ICMP echo reply is sent for both. I'm ashamed of myself, but now I know. It was suggested on #networking to either isolate the mirrored traffic to an interface that does not have IP enabled, or tag the mirrored packets with dot1q.

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• Is there a bash shortcut for traversing similar directory structures?

  - by Steve Weet

  The Korn shell used to have a very useful option to cd for traversing similar directory structures e.g. given the following directorys /home/sweet/dev/projects/trunk/projecta/app/models /home/andy/dev/projects/trunk/projecta/app/models Then if you were in the /home/sweet.... directory then you could change to the equivalent directory in andy's structure by typing cd sweet andy So if ksh saw 2 arguments then it would scan the current directory path for the first value, replace it with the second and cd there. Is anyone aware of similar functionality in bash. EDIT 1 Following on from Michal's excellent answer I have now created the following bash function called scd (For Sideways cd) function scd { cd "${PWD/$1/$2}" } EDIT 2 Thanks to @digitalross I can now reproduce the ksh functionality exactly with the code from below (With the addition of a pwd to tell you where you have changed to) cd () { if [ "x$2" != x ]; then builtin cd ${PWD/$1/$2} pwd else builtin cd "$@" fi }

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• Java framework "suggestion" for persisting the results from an Oracle 9i stored procedure using Apac

  - by chocksaway

  Hello, I am developing a Java servlet which calls an Oracle stored procedure. The stored procedure is likely to "grow" over time, and I have concerns the amount of time taken to "display the results on a web page". While I am at the implementation stage, I would like some suggestions of a Persistence framework which will work on Apache Tomcat 5.5? I see two approaches to persisting the database results. A scheduled database query every N minutes, or something which utilises triggers. Hibernate seems like the obvious answer, but I have never called stored procedures from Hibernate (HQL and Criteria). Is there a more appropriate framework which can be used? Thank you. cheers Miles.

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• Application Server or Lightweight Container?

  - by Jeff Storey

  Let me preface this by saying this is not an actual situation of mine but I'm asking this question more for my own knowledge and to get other people's inputs here. I've used both Spring and EJB3/JBoss, and for the smaller types of applications I've built, Spring (+Tomcat when needed) has been much simpler to use. However, when scaling up to larger applications that require things like load balancing and clustering, is Spring still a viable solution? Or is it time to turn to a solution like EJB3/JBoss when you start to get big enough to need that? I'm not sure if I've scoped the problem well enough to get a good answer, so please let me know. Thanks, Jeff

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• JavaScript distributed computing project

  - by Ben L.

  I made a website that does absolutely nothing, and I've proven to myself that people like to stay there - I've already logged 11+ hours worth of cumulative time on the page. My question is whether it would be possible (or practical) to use the website as a distributed computing site. My first impulse was to find out if there were any JavaScript distributed computing projects already active, so that I could put a piece of code on the page and be done. Unfortunately, all I could find was a big list of websites that thought it might be a cool idea. I'm thinking that I might want to start with something like integer factorization - in this case, RSA numbers. It would be easy for the server to check if an answer was correct (simply test for modulus equals zero), and also easy to implement. Is my idea feasible? Is there already a project out there that I can use?

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• Reported error code considered SQL Injection?

  - by inquam

  SQL injection that actually runs a SQL command is one thing. But injecting data that doesn't actually run a harmful query but that might tell you something valuable about the database, is that considered SQL injection? Or is it just used as part to construct a valid SQL injection? An example could be set rs = conn.execute("select headline from pressReleases where categoryID = " & cdbl(request("id")) ) Passing this a string that could not be turned into a numeric value would cause Microsoft VBScript runtime error '800a000d' Type mismatch: 'cdbl' which would tell you that the column in question only accepts numeric data and is thus probably of type integer or similar. I seem to find this in a lot of pages discussing SQL injection, but don't really get an answer if this in itself is considered SQL injection. The reason for my question is that I have a scanning tool that report a SQL injection vulnerability and reports a VBScript runtime error '800a000d' as the reason for the finding.

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• Diagonal of polygon is inside or outside?

  - by Himadri

  I have three consecutive points of polygon, say p1,p2,p3. Now I wanted to know whether the orthogonal between p1 and p3 is inside the polygon or outside the polygon. I am doing it by taking three vectors v1,v2 and v3. And the point before the point p1 in polygon say p0. v1 = (p0 - p1) v2 = (p2 - p1) v3 = (p3 - p1) With reference to this question, I am using the method shown in the accepted answer of that question. It is only for counterclockwise. What if my points are clockwise. I am also knowing my whole polygon is clockwise or counterclockwise. And accordingly I select the vectors v1 and v2. But still I am getting some problem. I am showing one case where I am getting problem. This polygon is counterclockwise. and It is starting from the origin of v1 and v2.

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• What was the most surprising failure of your 'Engineer's intuition'?

  - by Bubba88

  Hi! This may seem as an open-ended question but I'll surely accept the most impressive and upvoted answer ;) Basically, I could describe my own case - I just fail 5 times a day with my intuition cause very frequently I can be just not up-to-the-speed with my requirements/manager/team/etc. and I just have to make code quickly - that's why proper formalization in many cases stands aside. I want to gather some experience of yours - what was the most epic failure when you did rely on you implicit reasoning/intuitive knowledge/immediate perception etc. of course everything you describe should be related to programming/computers. It's mostly just to measure the danger of using that 'it's obvious..' words. I've made it com. wiki to be properly transformed after gathering enough views count. Thank you!

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• Which tutorial on Clojure is best?

  - by Steve Rowe

  I'm interested in learning Clojure. The Getting Started page on Clojure.net is pretty minimal. Is there a good language introduction or tutorial out there? Which would you recommend? Answer: I have watched the videos on youtube called Intro to Clojure. I don't recommend those. They are a little too brief and don't give a lot of background. The talks by Clojure creater Rich Hickey. I am finding the "for Java developers" version very useful.

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• My helper methods in controller

  - by FancyDancy

  My app should render html, to answer when a user clicks ajax-link. My controller: def create_user @user = User.new(params) if @user.save status = 'success' link = link_to_profile(@user) #it's my custom helper in Application_Helper.rb else status = 'error' link = nil end render :json => {:status => status, :link => link} end My helper: def link_to_profile(user) link = link_to(user.login, {:controller => "users", :action => "profile", :id => user.login}, :class => "profile-link") return(image_tag("/images/users/profile.png") + " " + link) end I have tried such methods: ApplicationController.helpers.link_to_profile(@user) # It raises: NoMethodError (undefined method `url_for' for nil:NilClass) and: class Helper include Singleton include ApplicationHelper include ActionView::Helpers::TextHelper include ActionView::Helpers::UrlHelper include ApplicationHelper end def help Helper.instance end help.link_to_profile(@user) # It also raises: NoMethodError (undefined method `url_for' for nil:NilClass) In addition, yes, I KNOW about :helper_method, and it works, but i don't want to overload my ApplicationController with a plenty of that methods

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• Named semaphores in Python?

  - by Boaz

  Hi, I have a script in python which uses a resource which can not be used by more than a certain amount of concurrent scripts running. Classically, this would be solved by a named semaphores but I can not find those in the documentation of the multiprocessing module or threading . Am I missing something or are named semaphores not implemented / exposed by Python? and more importantly, if the answer is no, what is the best way to emulate one? Thanks, Boaz PS. For reasons which are not so relevant to this question, I can not aggregate the task to a continuously running process/daemon or work with spawned processed - both of which, it seems, would have worked with the python API.

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• Code to make div appear after a certain amount of time.

  - by user307783

  Hi, I'm looking for code that makes a div appear after a certain amount of time on a site. Here's the sort of thing I'm talking about: <div class="container"> <div class="secretpopout"> This is the div I want to pop out after a couple of minutes. </div> </div> I'm relatively new to javascript and jQuery, but I'm assuming I will need to use the setTimeout or something similar. I've tried finding the answer online, but if someone could explain it in a way a designer (as opposed to a programmer) would get it, that would be great - ANY LIGHT shed on this would be greatly appreciated. Thank you.

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• How do I handle a JSON request returning a String in JQuery?

  - by knt

  Hi all, New to json/jQuery so sorry if this has an obvious answer. I'm doing an ajax request in jQuery that's something like: $.ajax({ url: theURL, dataType: 'jsonp', type: 'get', success: function(data) { alert("it's there"); } }); The request asks whether a given object is in a database. If it is, it returns something of the format: { "text": "duck", "canonical_name": "duck", "language": { "id": "en" }} However, if the object isn't there, it returns: Not Found As in...literally that exact string, not in any kind of json format as far as I know. Is there any way I can get my ajax to detect this? Right now it doesn't even seem to be acknowledging that it got anything back in the latter case. The json code wasn't written by me. It can possibly be fixed if this is not the correct format and there's absolutely nothing I can do from my end to work with this, but I'd really like to try to find some kind of workaround if possible. Thanks very much!

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• Convert mediawiki to LaTeX syntax

  - by Amit Kumar

  I need to convert mediawiki into LaTeX syntax. The formulas should stay the same, but I need to transform, for example = something = into \chapter{something}. Although this can be obtained with a bit of sed, things get a little dirty with the itemize environment, so I was wondering if a better solution can be produced. Anything that can be useful for this task ? This is the reverse of this question (graciously copied). Pandoc was the answer to that question, but probably not yet for this.

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• Desktop mono app and MVC/MVP framework

  - by tempy

  I am looking for a MVC/MVP (mvp prefferably) framework for my first mono app. There doesn't seem to be too much out there, but I have found the following: http://www.mvcsharp.org/ http://desktoprails.osl.ull.es/doku.php I've been looking into both for some time, and MVC# seems to be closer to what I want. The issue is that MVC# seems to be a .net project and not designed specifically for mono (as opposed to desktop rails), so I'm not 100% sure how it will play with mono. Also, it is under the Microsoft Public License (MsPL), and I am not sure how well that license will play with other components I intend to use that are gpl/mit/apache/etc. So if anyone has any experience with either of these frameworks in mono and can answer any of these questions, I would appreciate any feedback.

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• Need to devise a number crunching algorithm

  - by Ravi Gupta

  I stumbled upon this question: 7 power 7 is 823543. Which higher power of 7 ends with 823543 ? How should I go about it ? The one I came up with is very slow, it keeps on multiplying by 7 and checks last 6 digits of the result for a match. I tried with Lou's code: int x=1; for (int i=3;i<=100000000;i=i+4){ x=(x*7)%1000000; System.out.println("i="+ i+" x= "+x); if (x==823543){ System.out.println("Ans "+i);} } And CPU sounds like a pressure cooker but couldn't get the answer :(

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• [BUG] Bus Error - What causes this in Ruby?

  - by viatropos

  I have run into this error 5 or 10 times over the past few years and have never found a clear answer to this problem. Here is the error: $ rake db:migrate /usr/lib/ruby/gems/1.8/gems/libxml-ruby-0.9.5/lib/libxml_ruby.bundle: [BUG] Bus Error ruby 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin9.7.0] Abort trap The app I am running this in is using RMagick. I have run into this problem when installing ImageMagick a while ago, and when installing Nokogiri, and when installing MySQL. For Nokogiri it was because I needed a more recent version of libxml. What are your thoughts on this? Any fixes? How can I check the version of RMagick the project is loading? I am on a Mac, 10.5.8. Thanks for the help, Lance

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• a full-screen UIImagePickerController with the right scale?

  - by Kay

  Hi, I'm customizing my image picker controller and I want to have a full-screen viewfinder. I think this might be pretty an old topic and I found an answer here: http://www.gorbster.net/blog/archives/144 But what I want to know is if there's a way to achieve this without distorting the scale of the image. If I scale that clipped preview image, I'm distorting its original x-y ratio, and I want to avoid it. Is there a way to prevent the preview image from being clipped so that I could retain the original 1200x1600 ratio? Thanks!

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• jquery scrollTo refuses to work

  - by hasan

  hey, ive read all the scrollTo questions and couldnt find the answer. im trying to use the scrollTo plugin for a simple horizontal scroll (the site is horizontally designed). im using the following code $(document).ready(function() { $('#contactlink').click(function(){ $.scrollTo("#conta", {duration: 8000 }); }); }); as is obvious, contactlink is the anchor link while conta is the anchor where the window should scroll to. i know im missing something very obvious, but as im a beginner with jquery, id appreciate all the help i can get. is there any way to debug the functioning of the plugin? thanks

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• First time unit testing (in silverlight)

  - by Jakob

  Hi I've searched some other posts, but most of them assumed that people knew what they were doing in their unit testing, and frankly I don't. I see the idea behind unit testing, and I'm coding an silverlight application much in the blind right now, and I'd like to write some unit tests to kind of be sure I'm on the right path. I'd like to be able to use the SL4 vs 2010 silverlight unit test project template, to keep it simple and not use external tools. So what I need an answer for are questions like: what are the methods of unit testing? what are the differences between unit tests, and automated unit tests? How do I meaningfully unit test in silverlight? What should I be aware of while unit testing (in silverlight) ? Also should I implement some kind of IRepository pattern in my silverlight app to make unit testing easier?

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• NoSql Crash Course/Tutorial

  - by Chris Thompson

  Hi all, I've seen NoSQL pop up quite a bit on SO and I have a solid understanding of why you would use it (from here, Wikipedia, etc). This could be due to the lack of concrete and uniform definition of what it is (more of a paradigm than concrete implementation), but I'm struggling to wrap my head around how I would go about designing a system that would use it or how I would implement it in my system. I'm really stuck in a relational-db mindset thinking of things in terms of tables and joins... At any rate, does anybody know of a crash course/tutorial on a system that would use it (kind of a "hello world" for a NoSQL-based system) or a tutorial that takes an existing "Hello World" app based on SQL and converts it to NoSQL (not necessarily in code, but just a high-level explanation). I see this having one solid answer, but if you guys feel like it should be community wiki, I'll be happy to change it. Thanks! Chris

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• Using emacs across many hosts

  - by mbac32768

  On a daily basis I: use multiple workstations running either Linux, Windows, or MacOS X edit files on additional Linux hosts that are not any of the workstations mentioned above The only common element here is that the internet connects all of these hosts: workstations and servers. I can keep all of the config files in sync on my workstations too and can run an X server on all of them. What's the right way of running emacs? I don't want to sacrifice any features. In my ideal world I can type 'emacs foo.txt' on a remote host and some magic happens via X forwarding to display the file in my workstation's existing emacs session. Non-solutions tramp: when I'm manipulating a remote host an editor is just part of my workflow. I need a terminal open so I can run other commands quickly. tramp is all wrong for this. ncurses emacs: sucks, I want the graphical kind If you don't have a positive answer to my question, please don't just guess. Thanks.

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• nested page-faulting of user-space address in Linux

  - by shankar

  Hi, I would like to know if it is functionally wrong to page-fault a user-space address when kernel is running fault-handler to bring in a user-page. OS is Linux 2.6.30 Assume that both user-addresses are valid ( falling within vma , rw permission ) for the task. When I check the kernel code, i find that the kernel does not mind the nested fault if the faulted-addresses are valid and the fault did not occur in atomic-context or in irq handler. (I dont think the answer is cpu-specific, but I would add that i am interested in arm and mips ). eg : The scenario can happen if I print stack-data from page-fault handler. thanks shankar

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• Handling newline character in input between Windows and Linux

  - by Fazal

  I think this is a standard problem which may have been asked before but I could not get the exact answer so posting the issue. The issue is that our server is running on a linux box. We access the server over the browser on a window box to enter data into field which is supposed to contain multiple lines which user can enter by pressing the enter key after each line Abc Def GHI When this input field (this is a text area),is read on the linux machine, we want to split the data based on new line character. I had three question on this. Does the incoming data contain "\r\n" or "\n" If incoming data does contain "\r\n", the linux line.separator property (vm property) would not work for me as it would say "\n" and therefore may leave "\r" in the data. If "\r" is left in the data, if I open the file on a windows machine, will this mean a newline character? Finally can anyone tell me the standard way to deal with this issue?

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• How do I determine the revision number of an Android build?

  - by hermo

  I know how to get the API level, android.os.Build.VERSION.SDK_INT, but there are also several revisions of each level release, e.g. for 2.1 there's rev 1 and 2. How do I determine the revision of a build? The reason i'd like to know this is that I have a workaround for a bug in Android 2.1 (and 2.2), and this workaround will break the moment the corresponding bug is fixed. So right now i'm in the odd position of hoping that the bug won't be fixed (at least not until I can find an answer to above question).

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