Re: Merging relayfs?

[Andrew Morton <akpm@osdl.org>]

Steven Rostedt <rostedt@goodmis.org> wrote:
>
> I will also admit that my ring buffers lost one byte per page.  Because
>  I wanted to save on space with the accounting, and only had a start and
>  end pointer per page.  So when start and end were equal, the buffer was
>  considered empty and when end was one less than start, it was considered
>  full. But since end always pointed to an empty spot, it would still be
>  empty when the buffer was full, thus wasting one byte per page. But to
>  solve this, I would either have to add another variable in the buffer
>  page descriptor (adding at least one byte, but probably 4 bytes) which
>  would just be more waste, or I would have to make a complex system even
>  more complex (ie. adding a flag on the end pointer at the MSB to
>  differentiate between end being empty or filled).

Nope.  Just make the indices 32-bit numbers and let them wrap.

Full:		(tail - head) == size
Empty:		(tail - head) == 0
Add item:	buf[head++ & (size-1)] = item;
Remove item:	buf[tail++ & (size-1)]
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