This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.
more to come soon.
What is the point of HAL?
To merge information from various sources such that desktop applications can
locate and use hardware devices. The point is that the exact set of
information to merge varies by device and bus type. In order to do this, we
need to define a format for the information, hence the HAL specification.
We may read some stuff from the hardware itself, then add some info provided
by the kernel, then add some metadata from some systemwide files, then add
some data that has been obtained by the desktop and stored per-user, then
look at some blacklist, and finally we have a complete picture of everything
known about that particular device.
An extra value is that we can do this in an operating system independent way.
Stuff like this is important to the major desktop environments.
