Re: Merging relayfs?

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 2005-07-12 at 16:55 -0700, Andrew Morton wrote:
> 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)]

You know I knew someone would have an answer.  Look for version 0.2.1
comming soon :-)

Thanks,

-- Steve


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