This post is both an attempt at replying to
a bug against
telepathy-glib, but also an attempt at explaining what
Requires.private do (and don't).
I am using Evolution as my example here, not to pick on Evolution or its
authors in any way, but because it's a convenient example. Currently,
on Ubuntu Hardy,
evolution links against 75 different libraries.
Amongst those, we find
libz.so.1,
libXinerama.so.1 and many more.
I'll go out on a limb here and claim that Evolution does not call any of
the functions in libXinerama directly. Let that be the assumption from
here on.
An obvious question then is, why does
evolution link against
libXinerama.so.1 if it doesn't use it? To answer that question, we
need to go back in time to before we had dynamic linking. If you wanted
to build a binary like
evolution you had to have 75
-l statements
when you linked and you ended up with the whole code for Xinerama
embedded in your email and calendar client. For various reasons, we
stopped doing that and switched to dynamic linking where the
evolution
binary just contains a reference to
libXinerama. At some point we
also grew the ability for libraries to contain those references to other
libraries, so you don't have to hunt down all the dependencies of
libfoo when you are linking with it. We also got tools such as
libtool which try to abstract away a lot of the problems of building
on older platforms which don't support inter-library dependencies.
Now, since
evolution still doesn't use anything directly in
libXinerama.so.1 but just uses a library which in turn links against
libXinerama.so.1, it shouldn't be linking against it. Then why is it
linked with it? Again, we need to look back at history, and for this
part I am at least partially responsible.
pkg-config was originally written as a replacement for
gnome-config
and various other
-config utilities. Lots of libraries and
applications now ship
.pc files and we have a standardised interface
for querying those files. One of the problems the original authors of
pkg-config faced was the problem of dependencies. They added
dependencies so the authors of
gst-python-0.10 could say "We need
pygtk-2.0 too" and so the compilation flags needed for
gst-python-0.10
would also include those for
pygtk-2.0. Note that I'm using
"compilation flags" loosely here, I am not just talking about CFLAGS.
This did not fix the problem of inflated dependencies. Not at all. I
talked with some of the Debian Release Managers back in 2004/2005 and
we worked out a solution which should help us have correct, uninflated
dependencies since the then-current way of handling dependencies caused
big problems for migrations of packages between
unstable and
testing.
The plan was to introduce a new field,
Requires.private which would
not show up unless you passed
--static to the
pkg-config invocation
(since you need all libraries if you are linking statically). This
definition of
Requires.private was mostly useless since GNOME and GTK+
have a habit of including each other's headers. To make a long story
short, I changed the semantics so the
Cflags field from private
dependencies were included even when not linking statically.
A problem which
pkg-config does nothing to guard against in this case
is if you have
libfoo.so.2 linking against
libbar.so.1 and
libfoo.so.2 exports some of libbar's types in its ABI (and not just as
pointers, but actual structs and such). If libbar's soname is then
bumped to
libbar.so.2 and libfoo is rebuilt, libfoo's ABI has changed
without a soname bump. This is bad and will cause problems. If your
application is linked against both
libfoo.so.2 and
libbar.so.1,
you'll still get problems since
libfoo.so.2 then suddenly pulls in
symbols from
libbar.so.2. If you used symbol versioning, you would at
least not get symbol conflicts and your application would continue to
work, but you would have a spurious dependency and the package
containing
libbar.so.1 would be kept around until your application was
recompiled.
With this background, you might ask the question why we still have
Requires since it is seemingly useless. For C, it is useless in all
but the most special cases, just use
Requires.private instead (and its
sibling
Libs.private). Other languages have different semantics.
Some people use
.pc files for other purposes such as
gnome-screensaver having variables defining where themes and
screensavers go.
Hopefully this blog post has explained a bit about why we have
Requires.private and what the difference between this and their
regular counterpart is. If there's anything unclear, please do not
hesitate to
contact me.
Dear lazyweb, I have a question with regard to image manipulation. Given an rectangle image with a continous function on it (in my case, walking distance from a certain point), I can easily draw the contour lines of the function, i.e. for a given distance from the center mark all points that have this distance. This looks very similar to the contour lines of height map. I d like to morph this image now that all these contour lines are circles around the centers, but I don t have a good idea how to do that with a minimum amount of distorting. Any suggestions or pointers to algorithms are welcome.
For a long time I wanted to play with IPv6, but I never liked any of the tunnels I saw. This evening I started wondering if my Cisco 837 ADSL router cannot handle some form of tunnel.
I’ve been using an EEE PC since december, and people keep asking me if they should buy one. So here are some things you should know before making a decision.
Screen
The screen is small, but that’s OK. I couldn’t find many applications that didn’t work in 800×480. And for the remaining ones, you can usually use hacks such as running the app in a larger virtual desktop. Not ideal, but it works. Regarding usability, it’s not a too big problem. Jut expect to use many apps maximized, and use scrolling and virtual desktops a lot. (Important note: Xmoto doesn’t work!!)
Keyboard
The keyboard is probably a bigger problem than the screen (I hadn’t expected it to be a so big problem before buying the laptop). Every other keyboard seems to have HUGE keys after typing on the EEE PC keyboard. But with some training, you can type quite fast, even if probably not as fast as with a full size keyboard. The layout of the “special” keys is quite good (esp. the PgUp/Down, Home and End keys on the arrows. I should remap my other keyboard like that).
Battery, power consumption
One big problem with the EEE PC is that it consumes a lot of power while sleeping (using suspend to RAM). If you leave it sleeping for more than a few hours, expect the battery to be empty. That really sucks, especially since suspend to disk isn’t really a good option on such a device. Another problem related to power is that charging the battery is quite slow.
SDHC card reader
If you want to expand the storage capacity of your EEE PC with the SDHC port, choose your SDHC card carefully. There are only a few cards that work. The other ones will cause write error (they will work in read-only mode, so I’m using an external card reader to write, which sucks). A list of supported cards is available in the EEE PC manual.
Random Q&A
Q: I don’t have a laptop. Should I buy it?
A: If you want to do a lot of real work on it, it’s probably not a very good idea. There are faster (but bigger) laptops at around 450-500 EUR. They are probably a much better option. The EEE PC is perfect as a the second laptop you only bring to places where you want to stay connected, read email and surf on the web (like conferences and meetings).
Q: Does the VGA output works well?
A: Yes. And it uses an Intel video card which works like a charm with xrandr. I already gave several presentations and classes using it. The laptop can output 1280×1024 (maybe 1600×1200, not sure). The only problem is that you will only have the top-left part of your slides on the laptop’s screen, because of the smaller resolution there. Annoying if you plan to read your slides.
There is one particular aspect of Microsoft’s document format going through ISO process that I had a hard time to find a counter-argument against: “Well it is better to have multiple open formats, isn’t it?”. Last night when I was presenting in a Document Freedom Day event, I finally got one. When multiple standards exist in the same area, two options can exist:
I handle bug reports and email communication as soon as possible, but it
does not mean that it may take month or even more to get reply. I'm not
working full time on my free software projects, I do it only in my free
time. Besides this I have regular job and I also have a real life with
another hobbies.
So if you wrote me something, just try to be patient, sending another
emails to urge your issue won't help anybody. I will just have more
unread mail to process until I get to real work.
I am looking for a charity to receive regular donations. I would
like to support the environment and wildlife, rather than people
directly, and the 