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© FUOC • P07/M2101/02709 133 Free Software
Another one of Torvalds' innovative ideas was to develop two branches of
the kernel in parallel: the stable one (the second number of the version is
usually even, such as 2.4.18) and the unstable one (the second number of the
version is odd, such as 2.5.12) As ever, Torvalds is the person that decides what
goes into which branch (many of the most controversial decisions are related
precisely to this point). In any case, Linux doesn't have any planned deliveries,
in fixed timeframes: it will be ready when it is ready and in the meantime
we'll just have to wait. Surely by now, most readers will have realised that the
decision on whether the system is ready or not will be made solely by Linus.
The development method used in Linux has proven to be very effective in
terms of results: Linux is very stable and any bugs are corrected extremely
quickly (sometimes in minutes), as it has thousands of developers. In this si-
tuation, when there is a bug, the probability that someone will find it is very
high, and if the person that discovers it is not able to correct it, someone will
appear who will hit on the solution very quickly. To summarise, this shows
how Linux has thousands of people working on its development every month,
which is why its success is not altogether surprising.
It should be noted, however, that this way of working is very expensive where
resources are concerned. It is not unusual for there to be many mutually-ex-
clusive proposals for a new function or that a dozen patches are received for
the same bug. In most cases, only one of the patches will finally be included
in the kernel, which means that the rest of the time and effort put into the
patches by the other developers will have all been in vain. Linux's develop-
ment model is, therefore, a model that works very well in Linux but which
not all projects can permit themselves.
9.1.3. Linux's current status
In early 2007, Linux was at version 2.6, which included, in terms of impro-
vements made to version 2.4, NUMA (Non-Uniform Memory Access, used a
lot in multiprocessors), new filesystems, improvements to communication in
wireless networks and sound architectures (ALSA) and many other improve-
ments (if you're interested in the details of the changes in respect of previous
versions, you may consult "The wonderful world of Linux 2.6" [186]).
Linux's development model has undergone some changes over recent years.
Although the development mailing list is still the soul of the project, the code
no longer has to pass through the list, necessarily. One of the things that have
contributed to this in a large way is BitKeeper, a proprietary system that per-
forms revision control, developed by the company BitMover, strictly following
Linus Torvalds' recommendations. The use of this proprietary tool generated a
lot of controversy, in which Linus, true to form, demonstrated his pragmatism
again, as for him and many others, the CVS version control system was very
antiquated. The disagreements were brought to an end with the development
of git, a revision control system with similar features to BitKeeper that is cur-