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GSoC 2016: Summary

screenshot of the official GSOC 2016 Project page for this project
Screenshot of my GSoC 2016 project page

Intro, Outro and tl;dr

I participated again as a student in this years edition of the Google Summer of Code with Debian on the project APT↔dpkg communication rework. My initial proposal on the wiki details me and the plan, while this post serves as link hub and explanation of what I did. You can also find personal week-to-week posts starting with Day 0 right here on this blog, too.

The code for this project was already merged and uploaded to Debian unstable multiple times over the course of the summer, so everything described here later can be experienced directly. The official GSoC2016 final is 1.3~rc2, but APT always moves forward and I have no intention of leaving it alone, so this tag just marks the end of the GSoC2016 period and my return to "normal" contribution levels.

On a social front I finally applied for and shortly after received "Debian Developer, uploading" status. This is also the moment I want to thank Michael Vogt (mentor, apt), Julian Andres Klode (apt), Manuel A. Fernandez Montecelo (aptitude), Guillem Jover (dpkg), Enrico Zini (AM), the Debian Outreach team and the countless people I should have mentioned here, too, who have all helped me in many ways over the course of this GSoC and my entire Debian journey up to this point.

It was an overall great experience to work again on something as important as APT in Debian on a full-time basis. After two (very different) GSoCs in 2010 and now 2016 I can full heartily recommend to any student with a passion for open-source to apply next year. Perhaps in Debian and maybe in an APT project? We are waiting for YOU!


My first commit as part of GSoC was made on 25. April titled edsp: ask policy engine for the pin of the version directly (minor bugfix), the last commit I will be counting on 17. August titled methods: read config in most to least specific order (regression fix). Not all of them are directly related to the GSoC project itself (the first is), but "just" in the timeframe (like the last) but were handled as part of general emergencies or for similar reasons described later and/or in the weekly reports. This timeframe of 115 days saw a total of 222 commits authored by me + 9 commits committed by me for others (translations, patches, …). The timeframe saw 336 commits as a whole making me responsible for a bit shy of ⅔ of all APT commits in this timeframe with on average of nearly 2 commits each day. A diffstat run over my commits says "322 files changed, 11171 insertions(+), 5847 deletions(-)" consisting of code, documentation and tests (this doesn't include automatic churn like regeneration of po and pot files, which deludes the global statistic). As a special mention our tests alone changed by: "109 files changed, 2759 insertions(+), 1063 deletions(-)". In my weekly reports here on this blog I used ~10574 words (not including this post), another ~23555 words in the IRC channel #debian-apt and sometimes very long mails to deity@ and bugreports (~100 mails) [Not counting private chit-chat with mentor via IRC/mail].

APT External Installation Planner Protocol (EIPP)

The meat of the GSoC project was the ability to let libapt talk to (external) executables (called planners) which are tasked with creating a plan for the installation (and removal) of packages from the system in the order required by their various dependency relations, similar to how libapt can talk to external dependency solvers like aspcud via EDSP. The protocol (current, archive) details how apt and a planner can communicate. APT ships such an external planner already in the form of 'apt' which is "just" using the internal always existing planner implementation, but reads and talks proper EIPP. The major benefit is testing here as it is now possible to generate an EIPP request, feed it to different versions and compare results to find regressions and similar. It also helps in bugreports as such a request is now auto-generated and logged so that it can be easily attached to bugreports and a triager can use that file to reproduce the problem. Previously recreating the system state a user had before the failed upgrade was a very involved, error prune and time consuming task (actually fixing the problem still is, but at least the first step got a lot easier).

APTs good old planner implementation saw also the activation (and fixing) of many previously experimental options intended to optimize the process blocked previously by items of the next paragraph, which makes it look like a new planner now. Entirely new planners exist as prototypes, but they aren't suitable for real use yet due to not handling "edgecases" and being effected by bugs in dpkg. Summary: Everyone can create and work on his own planner in the programming language of choice and run it against realworld cases directly opening a competition space for the invention of future improvements.

APT↔dpkg communication

The other major building block and donor of much of the projects name. Assuming a planner has figured out a plan there is still much left to do which is of no concern for each planner but handled centrally in libapt: The actual calling of dpkg and interpreting its replies. That sounds easy enough, but if you imagine the need of thousand of packages to be installed/configured at once you fear hitting something as barebones as the kernels maximum allowed commandline length. That happened once in a while in the past so finding better solutions to that problem within easy reach (as in: existing in dpkg already, new interfaces for possible future use are a different matter) is in order. Other problems included the overuse of --force options, not communication the purge/removal intentions to dpkg, insufficient crossgrade handling and avoiding losing user configuration on conffile moves involving packages to be purged just to name a few. But also listening to dpkg in terms of how it processes triggers and how all this should be reported in the form of progress reports to the user especially if some steps aren't explicitly planned anymore by a planner, but left to dpkg to do at some point.

The result is mostly invisible to the user, expect that it should all be now slightly faster as e.g. triggers are run less and most "strange" errors a thing of the past.

Side projects, emergency calls and random bufixes

Not actually on my plan for GSoC and at best only marginally related if at all I ended up working on these to deal with important bugs on a "as long as we have a full-time developer" basis.

This includes hunting for strange errors if rred is involved in updating indexes, further preparing for a binary-all future, fixing SRV support, being the master of time, improving security by allowing it to be sidestepped sometimes, improving security by potentially breaking backward-compatibility a bit, stumble into libstdc++6 bugs, implement SOCKS5 proxy support and generic config fallback for acquire methods to be able to propose the mergeback of apt-transport-tor among very many other things.

A complete list can be found with the previously shared git-branch browsing starting at my first commit in the GSoC timeframe (see also statistics above).


I would love to keep working on APT full-time, but that seems rather unrealistic and all good things need to come to an end I guess, so the next weeks will have me adjust to a more "normal" contribution level of "just" in my (extended) free time again. I will also be casually "shopping" for a new money source in the form of a small job while returning to university which hasn't seen a lot of me the last few months and picking up some community work I had delayed for after GSoC. That means I will surely not keep my daily commit average up, but my journey here is far from over:

After many years in APT and Debian there is still something new in it to explore each week as both are evolving continuously – but most of it hidden in plain sight and unnoticed by the general public: Around the start of GSoC I was talking on #gsoc with an admin of another org who couldn't imagine that Debian participated at all as all projects Debian could offer would be bitsized in nature: It is just a distribution, right, not a real org producing value (slightly exaggerated for drama). I would like to concur with this view of course for obvious reasons.

My life would be massively different if I hadn't started to contribute to Debian and APT in particular ~7 years ago – even through I thought I wouldn't be "good enough" back then. I think its fair to say that I showed my past self that in fact I am. Now it is your turn!

Week 16: Constant Optimization

This week saw the release of 1.3~rc1 sporting my tor-changes disguised as general acquire methods changes I mentioned last week as well as the revamp of apt talking to dpkg (and back) I worked on the last couple weeks as part of GSoC. It doesn't include any new planner, a stub is still lying in a wip branch, but our good old planner looks and behaves slight different, so it feels like a new one – and surprising as it is: So far no bugreport related to this. Probably all user systems caught instantly fire! 🙂

So, the week was further used to get used to cmake, build and run apt on various porterboxes to fix testcase failures, fixing other incomings and especially pull some hair out while debugging the bug of the week which lends the title to this blogpost: A one word fix for an issues manifesting itself only in optimization level -O3 on ppc64el. Optimizations are evil…

Beside causing quite some time waste for this week as well as in previous years it is also closing a loop: I introduced this problem myself while being a GSoC student… in 2010. Time really flies. And I have no idea what I was thinking either… I could be describing more of these "tiny" bugs, but the commit messages tend to do a reasonable job and if you are really that damn interested: Feel free to ask. 🙂

This next week will be the last official in GSoC from a students POV as I am supposed to clean up all bases & submit my work for the final evaluation – this submit will be as a blogpost describing & linking to everything, which equals miles long and relatively soon, so that I purposefully have kept this one a very short one so you will have enough energy to bear with me for the next one.

Week 15: Onion ordering

The week started badly: I had for a long while now a dead 'e' key on my keyboard, but I didn't care that much… I just remapped CAPSLOCK, retrained my fingers and be done with it [I have some fucked up typing style anyhow]. All good, but at this week additional keys started to give up. You have no idea how annoying it is to not be able use the arrow keys. Many things I work with have at least the vim-keybindings, but even in vim picking an autocompletion becomes a nightmare (or navigating shell history)… So, replacement keyboard please! That took a while, especially replacing it as my laptop makes that extra hard it seems but oh well. All working again now! The c-key is actually working a bit too good (you have to only touch it now, which had me worried as it started out with producing and endless stream of 'c' out-of-the-box before I removed the cap once) but so be it for now.

As you might guess that wasn't the ideal work-environment and slowed me down (beside being annoying), so what I intended to do as a sideproject turned out to be covering most of the week. Mergeback of apt-transport-tor into apt? Yes, no, maybe? The first few responses by mail & IRC are in regards to the plan, but that still had the need for a lots of code to be written and refactored. I have to say, implementing SOCKS5 proxy support in apt was kinda fun and not nearly as hard as I had imagined. Slightly harder it was to get a setup working in which I could test it properly. Everyone knows netcat, but that really targets more text-based protocols, not binary ones like SOCKS5. Still, I managed to figure out how to do it with socat eventually, resulting in a testscript we can at least run manually (as it requires a specific port. Not every tool is as nice as our webserver which can be started on port 0 and reports the port it eventually picked for real). Playful as I am I even compared my implementation to others like curl, which our https method is using, where I ended up reporting minor bugs.

But why and why now you might ask: apt-transport-tor can be (surprise surprise) used to let apt talk to Tor network. Conceptionally that isn't incredibly hard: The Tor software provides a SOCKS5 proxy an application can connect to be done. Two years ago then apt-transport-tor was introduced only our curl-backed https method could do that & the intention was be able to make backports of that transport available, too, so even through I wasn't all that happy about it, we ended up with a modified copy of our https method named tor in the archive and as it is with most modified copies of code, they aren't really kept in sync with the original. I really want to get this resolved for stretch, so it slowly gets hightime to start this as if it turns out that I need to take over maintenance for it without previous-maintainer consent there is quiet a bit of waiting involved stuff like this should really not be changed last-minute before the freeze… you will find more details in the mentioned mail on the reasons for proposing this solution in the mail.

Beside, SOCKS support is actually a so much requested feature that the internet actually believes apt would support it already via Acquire::socks::proxy … which is and will also be in future wrong as there is no socks method we would configure a proxy for – if at all you configure a method like http to use a socks proxy…

Of course, bundled with this comes a bunch of other things like better redirection handling across methods and stuff, but that isn't really user visible, so I skip it here and instead refer you to the git branches if you are really interested. A few things I will surely also mention then the relevant code is in the archive so that interested peers can test…

On my actual battle front, the ordering progress was insignificant. I got lots of manual testing and review done, but not much new stuff. The problem is mostly that ordering is easy as long as the problem is easy, but as soon as Pre-Depends are entering the picture you suddenly have to account for all kinds of strange things like temporal removals, loops conflicting or-groups, … stuff you don't want to loose hair over while losing hair over your broken keyboard already. 😉

This week for realz, although target is now really more to merge the current stuff for apt 1.3. A new ordering algorithm is as detailed in the initial proposal buster material anyhow – and given all the changes in terms of trigger delaying and pending calls you are likely not to recognize our "old" ordering anymore, but more on this in the next two weeks as that will be the end of GSoC and hence I am going to look back at "the good old times" before GSoC compared to what we have now. 🙂

P.S.: This weeks weekend marks the start of a big wine festival in our state capital my family is one of the founding members of. I am "just" going to help building the booth through, so no giant timesink this time – just a couple hours – just in case you hear me saying something about wine again on IRC.

Week 14: This is CROSS!

Picture me as a messenger kicked into an endless pit of complexity by what was supposed to be an easy victim. It wasn't /that/ bad, but massaging apt to treat crossgrades right took some time – and then some more to request that dpkg would handle some of it, too, as it gets confused by multi-instance packages. Much like apt although that was just effecting apts progress reporting so not that bad… perhaps I am play-testing too much

In unrelated news I dealt with the two acquire bugs which started last week as such bugs are annoying & carry the risk of being security problems which would require immediate attention. Thankfully non of them seems to be one, but #831762 had me seriously worried for a while. Trivial in retrospective, but getting to a point in which you consider the possibility of that happening at all…

But back to the topic: There was one thing still needed to get our current internal planner a bit "smarter" by enabling options which existed for a while now, but were never activated by default, and that thing was simulation. While its kinda appealing to have the simulation only display what the planner explicitly told use to do, ignoring what would implicitly be done by the --pending calls we can't really do that as this would be an interface break. There are surely scripts out there doing funny things with this output so having it be incomplete is not an option, which in turn means that what I did internally for the progress reporting (and hook scripts) must also be done in the simulation. Easier said then done through as the implementation of it followed a direct approach running the simulation of each action as soon as the action was called rather than collecting all the actions first to post-process them (as I want to do it) and execute them only then. Add to this that this is a public class, so ABI is a concern… the solution I arrived at is slightly wrong, but is going to satisfy all existing callers (which is only aptitude in the archive thanks to codesearch.d.n) and reuses the "dpkg specific" code, which is a layer violation, but reuse is better than copy&paste without breaking ABI, so I am happy all things considered.

So, with that out of the way glory awaits: Changing the default of PackageManager::Configure from "all" to "smart"… and tada: It works! The simulation shows everything, the dpkg invocations are much shorter, trigger executions delayed, we rely more on --pending calls and progress reporting is properly moving forward as well! Not 100% production ready but good enough for a public wip branch for now (= wip aka: going to be rebased at will).

This also includes the barebones 'dpkg' planner I mentioned last week, based on that I was playing with ideas to find a more viable implementation (= handling Pre-Depends) but nothing of particular note produced yet. Maybe I can get something working this week – it is at least part of the plan beside polishing my wip branch – after leaving that pit that is… Hello, is anyone up there? Hello? Hello? …

Week 13: Progress reporting

On the public side of things I did a bunch of things this week which weren't exactly related to the GSoC project which were triggered by incoming mails (and IRC highlights) with bugreports and interesting whichlists, which isn't completed yet as there are two new responses with debug logs waiting for me next week.

I say that as I brushed up a smallish commit for merge this week which is supposed to deal better with triggers in progress reporting. That sounds boring – writing progress reporting stuff – but many people care deeply about it. While this one is more of a cosmetic change its conceptionally a big one: With the actions the planner proposed, apt builds for each package a list of states it will pass through while it is installed/upgraded/removed/purged. Triggers rain in this parade as we don't know beforehand that a package will be triggered. Instead, a status message from dpkg will tell us that a package was triggered, so if we don't want to end up in a state in which apt tells via progress report that it is done, but still has a gazillion triggers to run we have to notice this and add some progress states to the list of the triggered package – easy right? The "problem" starts with packages which are triggered but are destined to be upgraded to. A triggered package will loose its trigger state if it is unpacked, so our progress report has to skip the trigger states if the package is unpacked – we can't just exclude packages if they will be unpacked as it can easily be that a package is triggered, the trigger is acted upon and is upgraded "ages" later in this apt run.

My wip branch contains many more progress related commits as there is a big gotcha in the description above: I said "with the actions the planner proposed", so what about the actions the planner isn't proposing but will happen as part of dpkg --configure/--remove/--purge --pending calls? And what about hook scripts like apt-listbugs/changes which get told the actions to perform their own magic?

The solution is simple: We don't tell dpkg about this, but for our own usage we do trivial expansions of the --pending commands and use these for progress report planning as well as for telling the hookscripts about them. That sounds like a very simple and optional thing, but it was actually what blocked the activation of various config options I had implemented years ago which delay trigger execution, avoid explicit configuration of all packages at the end and all that which I could now all enable – a bit more on that after this hits the master branch. 🙂

I also looked into supporting crossgrades better. In apts conception a crossgrade is the remove of a package of arch A and the installation of a new package (with the same name) of arch B. dpkg on the other hand deals with it like a 'normal' upgrade, just that the architecture of the package changes. The issue with that isn't gigantic usually, but it becomes big with essential packages like if you try to crossgrade dpkg itself with apt: APT refuses to do that by default, but with enough force it will tell dpkg to remove dpkg:A and then it tells dpkg to unpack dpkg:B – just that there is no dpkg anymore which could unpack itself. At least in that case we can skip the remove of dpkg:A, but we can't do it unconditionally as that might very well be some part of an order requirement, so progress reporting should be prepared for either to (not) happen… That isn't finished yet and will surely leak into next week.

Next week will also see my freshly built planner 'dpkg' get a proper tour: With all the --pending calls it seems like a good idea to try to be extra dumb and have a planner just unpack everything in one go, let the rest be covered by --pending calls and see what breaks: Obviously the harder stuff, but I have two directions I would like to explore based on this minimal planner to make it viable. First I have to finish the crossgrading through, my usual self-review of commits and the bugreports I participated in this week want to trigger further actions, too… see you next week!

Week 11+12: Where did all the time go

Julian said that in his talk about the last year in APT in regards to (further) fixes to the performance of pdiff and apt in general. I want to say that about the last two week in general through. I was two days at the university (last two weeks of lectures even), a day helping moving, a day away with the young group, a combined day busy with mental and organisational buildup and teardown of that away-day, 5 days building, tearing down and in between manning our wine booth as well as other booths at a festival… Somehow that left only 4 days for day-to-day business like gsoc work… not ideal, especially if the plan isn't working out as it should either. I had to deal with a few issues uncovered by our testsuite caused (on non-amd64 architectures) more or less by the EIPP merge. Mind you, not actual hardcore bugs, but mostly: For some esoteric reason like additional lines in output the testcases are unhappy, but its not reproducible always and absolutely not on your local system.

Turns out that one of them was a deeper issue with how compression methods can be dynamically configured and how the testcases do this to force testing of certain aspects which interfered with me hardcoding xz-compression for EIPP – time-dependent of course as EIPP tends to run faster than /bin/false (no joke, as the errors were pipe write errors which only happen if the program we called closes the pipes aka exits). Sounds simple, but the fix is split over 6 logical commits (which all just change a few lines, but finding them is the trick…). Another dpkgs inability to change the architecture it believes to be native, while apt can do that easily and uses it in the testcases frequently.

Another issue was an a lot bigger bug in which apt ended up changing permissions, ownership & access/modification times on files it should actually only read through symlinks created by the file:// method. Finding and fixing this was an interesting walk in the kernel/libc API park as even if it isn't strictly needed to change the ownership of a symlink, it feels better too avoid to much of special casing if it can be helped and what we really don't want is singling out the Linux kernel against other kernels – I did that once accidentally (#738567) and try to avoid it ever since (that report is related by the way as that call would have been handy if it could have been used here…).

With the weeks so grossly derailed I purred some time into an issue with our relatively new SRV records support which was working only if the first connect would be successful, which is kinda against the point of SRV. Testing this was fun as I was actually convinced I would need a fullblown DNS server setup (much like we need a fullblown webserver setup so much that we implemented our own), but it turned out that its dead simple to add SRV records via dnsmasq, so that was easy to test (after I figured that out that is) at least interactively.

Also I implemented support for "install ./foo.changes" partly in response to the possibility of securing the download of individual debs question in the APT talk – now you can distribute a bunch of debs (and dscs) via a changes file, which can be signed (which the USER has to verify!) and includes the hashes of said files (which apt checks against). Mostly I was doing it for me through as I do local rebuilds at times (like dpkg with a fix for #830267) and picking the individual debs can be a bit annoying and with changes its slightly less bad.

Apart from that I looked into the progress reporting thing as intended and tried a few options, but that isn't all too easy given that apt is expecting to know EVERY action performed… I started with this, but I will probably tell you more about that next week as I fully intend to quickly make up for last two weeks, so I better get started right about now…

Week 10: That is plane wrong!

As a kid I liked Asterix as comic as well as in the animation films – I am not so fond of the actor films and haven't looked at the newer comics, but that is beside the point. I want to quote Obelix here: "These Brits are crazy!". Not because of the recent vote to leave the EU or because the english soccer team decided that this vote applies also to their play. No, I am thinking of the scene in the film in which the hero's walk down a street in search for a house and all of the houses in the street, the block, even the district look the same, but luckily they have the number, find the one and beat up the inhabitant only to be told that an 'I' is missing in the number…

After last weeks merge, I was told that "planer" doesn't mean what I thought it does. A planer is actually a type of machine to make stuff plane – which is again not making something into a plane to fly with it, but to make something plane so you don't get splinters (if its wood), all of this can be done according to a plan btw. What I meant is a "planner" – aka I was missing an 'n'. Perhaps only because I have light dyslexia, but I hate these language things. German isn't all around better in this: "The 'Planer' makes a 'Plan'." but the stuff can still be made 'plan' (even through 'planar' is what you usually hear and it hasn't the wood-meaning, you can just do this to the ground). But at least we don't drag planes or plants into this, the later being a masterpiece of word meaning all by itself… but enough of a "rant", I am pretty sure it all makes sense if I would look up history more than I did and in the end its just me trying to hide my embarrassment over such trivial mistakes being made by me for weeks…

Anyway, on the real topic of this post as I did more than just correcting this mistake (which did take a while through). Beside various things which are only slightly related or even not at all like: Not overriding an atomic file if the new file had failures in creation (oh my god, how did we miss that for so long?!?), various testing things, an overhaul of the autoremover code + implementing 'protect only the latest same-source provider' which has explicit benefits e.g. in terms of out-of-tree kernel modules (if built e.g. with module-assistant instead of dkms) as well as in other cases, fixing the handling of local deb files if it was previously already installed in that version as not behaving like a downgrade and finally a bunch of apt-key changes to make its badness more visible… which all went directly to git/master.

I started another of my wip branches for the things I am actually paid for to do: The plan was to tackle some "how apt invokes dpkg" things. Silly things like not setting --force-remove-essential on each and every remove/purge (if possible, there are non-default apt options which prevent apt from knowing which packages are essential in dpkgs view).

Also worked on codifying the --recursive usage for --unpack which sets up a symlink farm in a temporary directory and tells dpkg said directory instead of explicitly listing each and every package on the commandline explicitly (which can turn out to be quite long, see weeks earlier), but as mentioned back then this doesn't work yet unconditionally as dpkg has a bug in its ordering code, so for the time being apt needs to be nice and still help dpkg out here (that is the type of stuff I mentioned in my proposal as likely hindrance of using another planner for stretch already).

I also began saving, clearing and restoring dpkg selections before/after running dpkg so that a planner can eventually outsource the removal orders to dpkg. That is quite a dance as these selections are user settings "for the future" which we can't just discard, but we also can't just ignore them as they can include purge selections and if we would not unset them before calling dpkg in a new world order apt would implicitly instruct dpkg to perform removals the user hadn't agreed to… frankly, its a freaking mess, but the interface exists so I have to make due with what we have rather than what we "will like to be have had" if only there was a timemachine.

I am somewhere deep down in this clusterfuck, but I see light at the end of the tunnel – or perhaps that is just an oncoming train. Hopefully I am out of this by next week. I also want to give --no-triggers a chance again, a few years back I implemented support for it, but it never really saw the daylight thanks to bugs in dpkg and elsewhere, but perhaps now is a good moment for retrying. It does deal the final blow to sensible progress reporting through, so I would need to figure something out for that, too… we will see; planning plane plans isn't always working out for me.

(This weekend I have a daytrip with ~70 kids with the usual last minute emergencies and much needed decompress afterwards, so reports might be delayed and my replies/work even more off business hours than usual).

Week 9: Evaluate me please

Last week was as mentioned midterm evaluation, so my mentor is required to judge me and I am required to judge my mentor. I still remember last time so I was actually a bit surprised to see just a handful of questions and my "favorite" wasn't one of them anymore. The freeform answers even had a sizelimit of 2000 characters. Basically the same question topics through: How is the mentor & how are you doing. Most interesting perhaps is that most of the answers as I understood it aren't shared with the Orgas the students work for. Just the mentor judging is. Still, the form claims to be fillable in 10 minutes, I took considerably more time constantly rewriting and hunting for better words.

Not unlike what I did the rest of the week to the EIPP code, brushing over it, reordering and merging commits into potentially more logic units and finally testing and also fixing the bugs I ended up (re)introducing with my constant code shuffling – but enough is enough, I just pushed that stuff into master for everyone to see and work with (it was available last week in my wip branch as said, so that is just the more public-public. Still, master is always a big deal as it suddenly becomes "code which is supported" instead of "code I can freely change at will as nobody cares").

So, with the next upload of apt to experimental you will have funky stuff to play with, which you already know all about from the last weeks, but lets summarize how to opt into becoming my testlab monkey:

Individual apt(-get) calls [simulation or not] can be performed externally with the commandline switch --planner. The only available one at the moment is 'apt' which does the same as the internal one, just externally (okay, I am lying, there are two as there is also 'dump', but that isn't really a good planner…). Externally planed or not the EIPP scenario of the last request is stored (xz-compressed) in /var/log/apt/eipp.log.xz, so if you end up running into a ordering bug, you can now attach this file for perfect reproducibility which was considerably harder in the past with directing the user to grab a backup of the dpkg/status file from before the failure and hope that the mirrors are still in a state to reproduce it. Now, this file can be piped into the planner: /usr/lib/apt/apt-helper cat-file eipp.log.xz | /usr/lib/apt/planners/apt and out comes hopefully a bunch of progress messages (which in case of apt aren't displayed yet as I haven't really found a good place were it would also make sense & not sure if there is much point after all) and various actions to be performed via a protocol described in all its glory details in the documentation.

(That isn't all I did, but its the only thing you can play with … the rest is playing with you my little monkeys 😛 )

That should keep you busy for a week allowing me to continue investing some time into how dpkg itself is called by apt (with the plan in hand). There are 'old' ideas of how to change/improve it, some implemented but disabled, some not and some blocked by dpkg bugs. EOE will need some of these to work at all but that will be explained later… see you next week!

P.S.: It was also very hot & sometimes very rainy this week, a small british majority made me, themselves and the rest of the world feel sad and the french have strange number formats, but I can't and don't want to talk about everything in a little status update, can/should I…

Week 8: I have a new e-mail address

So, today I got a new e-mail address. That is an interesting development as I wasted a bit of time into stetting it all up, but as that is basically already Week 9 material, lets recap last week:

As suspected it was a bit slower than last week, due to setting up and "hanging out" at our wine booth (tear down tomorrow), so I was happy to had some buffer. Actually, I ended up not doing what I planed but "wasted" most of the week on debugging http strangeness's, avoiding libstdc++6 bugs and most importantly work on acquire system in relation to repositories apt considers insecure or weakly secured and how packages with the same "problems" are dealt with. Sounds boring and it pretty much is, but people run into this issue (there is a certain joy in fixing a bug before it is "officially" reported) and while we talked about it for a while, nobody really did it…

Anyway, that meant that my EIPP merge I was hoping for isn't done yet – it merges cleanly on top of master & all tests pass, but I hadn't the time to review it again (and again and again – attempted perfectionism isn't even close in describing what I tend to do with patches; and they are still riddled with bugs…)… so, I pushed it to a wip branch for now as it is midterm evaluation week now.

As said earlier that branch is concerned with adding EIPP itself (20 files changed, 1120 insertions(+), 22 deletions(-)) only, a lot of code already moved to master in earlier weeks as part of EDSP fixes, ordering code changes and stuff (a bit harder to calc as its intermixed with other changes I did in my free time on other things I have to subtract, but the neutralized running total in that branch should be around: 73 files changed, 2423 insertions(+), 1002 deletions(-)).

So, now that I mentioned it, with midterm this week I will have to pass some formalities (filling questionnaires mostly) I will probably talk about in the next report, I will surely get my EIPP merge done early on & start the last part of my GSoC project: Introducing the new planner 'eoe' (acronym suggested by Michael, meaning too be revealed later). Oh, and I will probably play a bit with my new account given that I should have more time this week. 🙂

Week 7: Hey, you are leaking!

Remember how I talked last week about how things should be different planners rather than option? Well, while writing I was doubting my self already and only a few hours later I actually did what I said I would probably not do. EIPP has now two options: A boolean Allow-Temporary-Removal-of-Essentials (guess what it does) and a tri-state Immediate-Configuration, which defaults to being unset, so a planner can do whatever it wants to, while yes and no activate or disable it for all packages.

That seems inconsequential, but while these options will not make sense for every planner (which is fine), for "general purpose planners" like our internal one its either this or 6 slightly differently named planners which could get messy…

Messy… remember that I said progress would be printed? Turns out, I was actually wrong, that wasn't progress. Or, well, it was, but not of the planner but of the apt instance itself. You see, the EDSP/EIPP binaries created by me all drop their privileges soon after they are called. They simple don't need root-rights. Its not much in terms of security, but it can prevent mistakes, so that is a plus. And that progress actually was a mistake prevented in normal execution by the dropping, but our testcase environment is special enough that an unprivileged user has rights well above the usual (like writing to the pretend /). So what it tried here was updating the binary caches with the protcol data… not a problem as the next apt run will see these caches as invalid and recreate them (which was the cause for the progress line), but it is a pointless action and easy to prevent. As that worked so well I also made it so that EDSP-like protocols default to privilege dropping as supposedly non of them really needs rights, but dropping is hard to implement… it is configurable through so if one of them needs rights (like dump) it can keep them a bit longer.

So, with our internal solver mostly working as an external one I shifted slowly to working on the surroundings. EDSP-like protocols can now generate and save a (compressed) copy of a scenario – in case an external solver/planner is used its input is saved like as if it would be called via tee and if the internals are used a scenario is generated and put on disk directly. That can be handy for all sorts of things, but mostly for debugging and bug reports. It was always possible to call a special 'dump' solver/planner who streamed its input to a file and produced an EDSP-understandable failure, but while for EDSP this is okay as a solution you don't like can be NACKed and the setup repeated as often as you want to (which is why logging isn't enabled for it) a bug in EIPP means usually a failure in the installation process which has modified the problem space already… so storing the scenario here allows for easy retrieval of this earlier state.

I also started on changing the way apt calls dpkg "for real". The planner is responsible for the order, but I decided that this is still rather "abstract" (e.g. no difference between remove and purge). The first thing I did is rather simple: As apt calls "dpkg --configure -a" at the end of its operation since 'recently' (= last stable release) it could stop explicitly configuring the last batch of packages before that, which tends to be a giant list. So giant, that apt actually has code to check if this all "fits" into the call as commandline have a size limit. On my system it reports ~2 MB (try e.g. with "xargs --show-limits") which seems like enough for everyone™, but that value could be (a lot) smaller and there are old stories of this happening… as with splitting it might fit again, but the chance of exploding also skyrockets. Anyway, the 1.3~exp2 release (in [surprise surprise] experimental) has this change. I also explored using --recursive on a softlinkfarm for unpack/install instead of mentioning every package explicitly as this is also in danger of hitting the limit, but while I have code working I hit (with our test-bug-740843-versioned-up-down-breaks) a dpkg bug in what Guillem identified as a problem in the Multi-Arch handling. The solution for apt would be to number the deb packages so they are sorted correctly, but that of course misses the point as ideally we (as in apt) don't want to micro-manage that much anymore meaning so we want to pretend here that we don't know the right order (as with a different planner we might really don't know).

In terms of overall progress: Our internal-as-external planner survived its first big test: It took care of an ~800 packages upgrade of my main system – that is how much I trust myself – without an issue. In fact the solution it calculated was very slightly better than what the internal produced [remember: It is the same code!] probably thanks to the reduced problem space and the different order in which versions are presented.

I also found a few file descriptor leaks (in EDSP, dpkg calling debugging and elsewhere) and cleaned up code slightly, so all in all a quite busy and good week. With an eye on the next that was pure tactic through: Next weekend is "Strawberry Festival" here which means my family is having a wine stall there which also has to be assembled first & soccer EM is running, so especially the earlier two items will eat time which is why I aimed for a "buffer" last week, so don't get your hopes up I can keep that production rate for this week. 😉

This week I will see about bringing EIPP to production state codewise to merge it to master. There are still things left which should be done, but before I do deeper modifications in the actual calling of dpkg I would like to have EIPP in so that I don't have to "maintain" two branches (and as it survived the big test, its "ready"). These call modifications surely will have effects on EIPP as well – currently a planner can only issue unpack, configure and remove commands, but there is also the unpack & configure combining --install which should be exposed (and unpack which is internally called install renamed).

See you next week!