On Fri, Jan 13, 2017 at 08:08:27PM +0000, Al Viro wrote: > Because it's "truncate to size", not "throw everything up to that point > out". > > We have some amount of data pushed into pipe (in this case - 0) and we > have some buffers allocated by ..._get_pages() past the end of it. > Some of that we want to keep (again, in this case - none) and have the next > copy_to_iter() go after those, the rest we discard.
PS: 'size' argument of iov_iter_advance() is the second "some" in the above - we tell it how much we want to advance by and everything past that point is, in case of PIPE_ITER, discarded.
