Combining ikiwiki and Twitter’s bootstrap
Just because Julien did it, I moved my website to almost the same design now. Still using ikiwiki, of course. I’m still missing a few things, such as marking the currently active page in the menu, but I hope to get that done as well soon. Go to http://jak-linux.org/ to see it.
Looking for HP Touchpad, Intel tablets, and other devices
If someone in Germany (or want to send it to Germany [at low costs]) still has (new) Touchpads to sell, I’d buy one or two of them at the reduced price (16GB: 99€, 32GB: 129€), or take them for free.
I promise that I will not sell them to others. I’m interested in WebOS, in running Debian and/or Ubuntu on those devices (for the extra fun factor), and lend it to family members for surfing, etc.
I also take other tablets and smart phones and various kinds of ARM and PowerPC hardware (I guess that’s all that’s interesting for me) for free, just send me an email if you have some and want to give them to me. This applies to Intel stuff as well, I’d really like to get some kind of WeTab/ExoPC, but can’t buy one currently (and they’re probably to outdated hardware-wise for buying to make sense).
World, Space, and Licenses
Common licenses for software include the term “worldwide”. Now, what does worldwide mean? The problem with the term worldwide is that it is ambigous and depending on it’s interpretation, violates against DFSG 6 which states: “No Discrimination Against Fields of Endeavor”.
The reason: Space travel. If we take the term worldwide to mean “everywhere on earth”, the license becomes non-free, as it prohibits the use outside of this planet. Affected by this problem are the patent section of GPL-3, the Apache 2.0 license, the CC licenses, the GFDL, and probably also others.
Now what should be used instead? Universal? No, that wouldn’t work in case there are multiple ones (while travelling between them (if they exist) could be impossible, it would still be a restriction). The correct team would probably be “omniversal” meaning “everywhere in the omniverse”. But really, avoiding locations is probably the best way.
In any case, if you have received software from me under a license that uses the term “worldwide”, you can treat worldwide as everywhere, and are thus free to use it outside of earth (and other planets).
dh-autoreconf v4 released, patching ltmain.sh for as-needed support
Yesterday I released version 4 of dh-autoreconf, fixing two bugs, and introducing a new feature: Patching ltmain.sh to make -Wl,–as-needed work.
For this new feature, run dh_autoreconf with the –as-needed option. dh_autoreconf will then patch all ltmain.sh equal to the system one (which should be all ltmain.sh files if libtoolize ran before or via dh_autoreconf). On clean, dh_autoreconf_clean reverses the patch again.
So, if your package runs autoreconf, and patches ltmain.sh via a patch you can now do this automatically via dh-autoreconf and be future-proof.
The only problem is that this might break once the patch no longer applies to libtool, at which point I need to update the package to include an updated patch. A solution for this problem would be to include the patch in libtool itself, as I proposed in Bug#347650.
In case this works well, the option could also become the default which would make things even easier.
0x15 + 1/365
Yesterday was my 21st birthday, and I received all “Hitchhiker’s Guide to the Galaxy” novels, the five ones in one book, and the sixth one written by Eoin Colfer in another book. Needless to say, the first book weights more than an N900. I did not read them yet, so now is the perfect chance to do so. Yes, I did not know that 25th is towel day, sorry for that.
I also bought a Toshiba AC100 before my birthday, a Tegra 2 based notebook/netbook/”web companion” with 1 GHz dual core ARM Cortex A9 chip and 512 MB RAM. It runs Android by default, and had a price of 160€ which is low compared to anything else with Cortex A9. It currently runs Ubuntu 11.04 with a specialised kernel 2.6.37 from time to time, without sound and accelerated video (and not functioning HDMI). Mostly waiting for Nvidia to release a new binary blob for the video part (And yes, if you just want to build packages, you can probably get happy without those things).
Another thing happening last week is the upload of python-apt 0.8.0 to unstable, marking the beginning (or end) of the API transition I started more than a year ago. Almost all packages not supporting it have proper Breaks in python-apt [most of them already fixed, only 2 packages remaining, one of which is "maintained" (well, not really maintained right now) by me], but there may be some which do not work correctly despite being fixed (or at least thought to be fixed).
If you know any other interesting thing I did last week, leave a comment, I wrote enough now. And yes, WordPress wants to write a multiplication sign instead of an x, so I had to use x instead.
Project APT2: new cache format and small things
I did not write much code or merge much of my prototype code, but some things happened since the last blog post about APT2 specific things in August and I forgot to write about them.
First of all, I dropped the GVariant-based cache. The format strings were simply getting ugly long and were not very understandable, performance was just much too slow (needing more than a few nanoseconds for a package lookup is obviously too slow for solving dependency problems); furthermore, building the cache was also slow and complicated because we needed all attributes of an object at once to pass them to GVariant, leading to ugly API.
I replaced the GVariant cache with one that can be easily mmap()ed and is described completely in C. It’s derived from APT’s cache design (but more robust, as it includes the size of the cache and we can thus detect to small files, although that’s scheduled for the next ABI break in APT as well), but has fewer duplicate data, and uses arrays where APT uses linked lists. The reason for arrays is simple: They take up less space and can be represented naturally in Python and other languages using array-based lists. The cache also contains a coalesced hash table which does use a linked list, but that one is a bit different, as it is for searching only and not exposed. Everything non-stringy is 64-bit aligned in order to keep things as simple as possible. All integers are fixed size, thus the format is architecture-independent if you fix byte orders. The format is described at http://people.debian.org/~jak/apt2-doc/apt-Cache-Format.html.
I stole one more idea from cupt and changed the configuration system to verify types of variables. APT2′s configuration system knows more types than cupt’s, though, including regular expressions, directory and filenames (i.e. it does not let you store a value /d/ in a file variable), strings (which store everything), unsigned and signed integers, and boolean options; all of which are checked when parsing files (producing warnings) or command-line options (producing errors).
I have also simplified the type world by removing all iterator types except for one, replacing them with get_thing() and n_things() functions in the objects holding the arrays. Makes cool bindings slightly harder, but makes the C API much easier to use from C.
Most things expected from a package manager are still missing, but what is there looks good in most cases (especially AptConfiguration has a nice API, and no complaints from valgrind anywhere). Currently I am working on Python bindings so I can interact with the functions easily and check things in an interactive fashion; and I am also writing a document explaining the concepts behind APT2, drafts at http://people.debian.org/~jak/midlevel.pdf. I also have some more code pending further thoughts (including complete index parsing), but it might still take some time before I have something usable in the wild.
On other package managers: From time to time I also use Cupt, look at Cupt code, hack Cupt code, and report bugs against Cupt. I still do not really understand the (extreme) nesting of directory structures in the source code, why there are so (extremely) many source files split all over them, or the general concepts of Cupt, but I can hack together what I need for my personal testing. I also play with yum whenever I end up on a Fedora system (which happens from time to time).
underscores and undefined behavior
As everyone should know, underscores in C are not cool, as they cause undefined behavior per 7.1.3:
All identifiers that begin with an underscore and either an uppercase letter or another underscore are always reserved for any use.
[...]
If the program declares or defines an identifier in a context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved identifier as a macro name, the behavior is undefined.
Yet, they are widely used everywhere. Here are some examples:
- inclusion guards in GLib:
__G_VARIANT_H__ - internal Python functions:
_PyUnicode_AsString - various macros in APT:
__deprecated,__hot
All of this triggers undefined behavior and is thus uncool. Of course in APT, it’s most stupid, as we do not have any namespace and could thus
end up redefining things we should not much more likely then the other two.
But why were those solutions chosen in the first place, and what is the alternative? I cannot answer the first question, but for the second one, the obvious alternative is to use trailing underscores:
- inclusion guards, defined behavior:
G_VARIANT_H__ - internal functions, defined behavior:
PyUnicode_AsString_ - various macros, defined behavior:
deprecated__,hot__
Then there is another class of reserved identifiers with underscores:
All identifiers that begin with an underscore are always reserved for use as identifiers
with file scope in both the ordinary and tag name spaces.
Meaning that everything except for parameters, local variables and members of structs/unions that starts with an underscore is reserved. So, if you happen to create a variable _mylibrary_debug_flag, you trigger undefined behavior as well. And while we’re at it, do not think you can create a type ending in _t: POSIX reserves all identifiers ending in _t for its own use.
In summary, whenever you write C and want to be 100% safe of undefined-behavior-because-of-naming, do not start any identifier with an underscore and do not end any identifier with _t.
last two weeks
The last two weeks, two new python-apt releases were made. 0.8.0~exp3 did not add much, but 0.8.0~exp4 added some new bindings for our friends at the mancoosi project. I also committed several fixes to the APT repository, but did not upload them yet.
In #debian-devel, some people (including me and others on the Debian side; and sladen, sabdfl for the Ubuntu side) discussed the Ubuntu font license which is considered non-free by Debian, due to extreme naming restrictions in section 2 (unmodified versions must keep the name, slightly modified versions must keep the name and add something). Some consider those restrictions equivalent to invariant sections. After we discusses the font license, we quickly got to discuss Doctor Who and time travel, as those two are obviously connected.
Some other things happened as well, like closing more bugs, but all in all, the last two weeks where a bit less intensive than the two weeks before them.
this week: apt 0.8.14 (regex pinning), stable updates, and bug triaging
python-apt 0.8.0~exp2 bug fix release
On Tuesday, I uploaded python-apt 0.8.0~exp2 to experimental, fixing about 10 bugs reported in Ubuntu and Debian bug trackers. It should know even convert integers correctly on all architectures, previously we could have passed long via varargs where int was expected.
Bugs
Until Thursday, I went through the bug list in Launchpad and closed/fixed/reassigned/merged about 100 bugs in APT and python-apt.
APT & python-apt updates for squeeze
Today, I uploaded updates of apt and python-apt to stable. They include support for xz and parsing multi-arch dependencies, as wanted by ftpmasters.
APT 0.8.14 and wildcards/regular expression pinning
Today, I uploaded apt 0.8.14 to Debian unstable, introducing support for pinning using glob() like Syntax and POSIX extended regular expressions. Let’s say we want to pin all packages starting with gnome or kde to 990. The following example does this, using glob-like patterns for gnome, and a regular expression enclosed in / for kde:
Package: gnome* /^kde/
Pin: release a=experimental
Pin-Priority: 990
This closes 10-year-old Bug#121132 in Debian. Have fun with this feature, but please note that it may not be the fastest thing on earth, as it checks every package in the cache on initialization of such queries, which may take a few 10 ms.
Since some time already, it’s also possible to use such expressions for the Pin field. Thus users of Ubuntu releases could use the following piece of preferences to pin all packages in archives starting with lucid (e.g. lucid, lucid-updates) to 990:
Package: *
Pin: release a=lucid*
Pin-Priority: 990
Those types of pins do not have the negative performance impact of complex expressions in the Package header, as they are only checked against a smaller set of packages, or if “Package: *”, simply checked against the package files in the cache.
