searching code for combination of vector

For a given numeric vector v of length n and sum s, is there a 
ready-to-run code that returns every combination of v in n summing up to 
s? Example for n=3 and s=2:

v <- c(2, 0, 0)
# find some coding here that returns
[1] 2 0 0
[2] 1 1 0
[3] 1 0 1
[4] 0 2 0
[5] 0 1 1
[6] 0 0 2

Thanks

S?ren