How to apply patches without a full source tree?

["Damon McMahon" <inst_karma_(_at_)_hotmail_(_dot_)_com>]

Greetings,

I'm wondering if there is a reliable way for a non-developer such as I to 
figure out what parts of the source are required to recompile userland code 
after applying a patch?

My situation is an old Pentium-75 box acting as a firewall for a small 
workgroup. Due to lack of HDD space and the general bad-ideaness of having a 
complete source tree sitting on such a box, I want to be able to extract 
only the necessary parts of the source in order to patch and rebuild.

With most patches I can do this, but every 1 in 6 or so seems to have 
dependencies which I can't work out. In this case it was one of the cvs 
patches [eventually compiled by progressivley extracting more and more of 
the source until it built] and the 009_kerberos.patch [still no luck].

> From my reading of the anoncvs FAQ the only workaround seems to be to 
extract the complete source from src.tar.gz to a CD-R and then perform a 
union mount:

% mount -t union -o -b /mnt/cdrom /usr/src

I guess if I have to do this then I will, but is there an easy way to 
predict the dependencies from a cursory examination of the contents of the 
source tree?

Many thanks in advance for any wisdom provided.

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