Rightfully is does...
But is think it is a prototype of a function.
But think about it - it does not makes sense to have an
extern declarationof a variable in an exported header.
There is no way that userspace can access this variable
from user-space and therefore the declaration of the variable
needs to be moved to a kernel-only header file.
So if you touch this I would ask you not to consider a single line
in jffs-user.h - but rather take a critiacal look at the whole
file and fix any issues there is.
And then to send it to the mtd people (dwmw2).
I did not look at the file but just looking at yout patch
the "undef jemode_to_cpu" looks fishy in an exported header.