git equivalent of 'svn update'

[Steve Kargl]

In the git world, what is the equivalent of 'svn update' 
within a subdirectory of the /usr/src hierarchy.  In the
svn world, one could do

% cd /usr/src/sys/dev/bge
% svn update

and this would only grab the changes under sys/dev/bge.

% cd /usr/src/sys/dev/bge
% git pull

grabs all changes under /usr/src, which now means that /usr/src
does not match the installed world when I want are the recent
changes to bge(4).  

-- 
Steve