Re: [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2]

From: Linus Torvalds
Date: Sun Oct 27 2019 - 10:04:03 EST

This still has signs of that earlier series:

On Wed, Oct 23, 2019 at 4:17 PM David Howells <dhowells@xxxxxxxxxx> wrote:
> if (rem >= ibuf->len) {
> *obuf = *ibuf;
> ibuf->ops = NULL;
> - pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
> - pipe->nrbufs--;
> + tail++;
> + pipe_commit_read(pipe, tail);
> } else {
> if (!pipe_buf_get(pipe, ibuf))
> goto out_free;

with those odd "pipe_commit_read/write()" helpers.

They make no sense, and they don't make things more legible.

It's shorter and more obvious to just write

pipe->head = head;

than it is to write

pipe_commit_write(pipe, head);

Even when the addition of the notifications, it's all under the
pipe->wait.lock, so it's all just regular assignments.

Now, if at some point it starts doing fancy lockless things, at _that_
point the updates might become more complex, but that's a potential
future thing that wouldn't be relevant for a while, and isn't a reason
to make the code more obscure now.