Re: splice() from /dev/zero to a pipe does not work (5.9+)

[Linus Torvalds]

On Fri, May 7, 2021 at 12:17 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> Umm...  That would do wonders to anything that used to do
> copy_to_user()/clear_user()/copy_to_user() and got converted
> to copy_to_iter()/iov_iter_zero()/copy_to_iter()...

I didn't mean for iov_iter_zero doing this - only splice_read_zero().

> Are you sure we can shove zero page into pipe, anyway?
> IIRC, get_page()/put_page() on that is not allowed,

That's what the

    buf->ops = &zero_pipe_buf_ops;

is for. The zero_pipe_buf_ops would have empty get and release
functions, and a 'steal' function that always returns false.

That's how the pipe pages are supposed to work: there are people who
put non-page data (ie things like skbuff allocations etc) into a
splice pipe buffer. It's why we have those "ops" pointers.

              Linus