FROMLIST: ring-buffer: Introducing ring-buffer writer

A ring-buffer writer is an entity outside of the kernel (most likely a
firmware or a hypervisor) capable of writing events in a ring-buffer
following the same format as the tracefs ring-buffer.

To setup the ring-buffer on the kernel side, a description of the pages
(struct trace_page_desc) is necessary. A callback (get_reader_page) must
also be provided. It is called whenever it is done reading the previous
reader page.

It is expected from the writer to keep the meta-page updated.

Bug: 357781595
Link: https://lore.kernel.org/all/20240911093029.3279154-3-vdonnefort@google.com/


Change-Id: Ib006ff19d79a5b2559b09661fba7bcd426ef8cba
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>