On Fri, Jan 13, 2017 at 11:33:18AM -0800, Linus Torvalds wrote: > What am I missing?
The fact that we want to free the _tail_, not the beginning of the damn thing. > Why is "pipe_advance()" written in that incomprehensible form? Why > don't we do the pipe_buf_release() as we advance through it, instead > of doing it at the end? > > Also, the line > > buf->len = size; > > in that pipe_advance() function looks buggy. "size" is how much we > *remove* from buf->len, shouldn't we update buf->len by subtracting > size? 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.
