Re: New version of frlock (now called seqlock)

[Andrew Morton <akpm@digeo.com>]

Stephen Hemminger wrote:
> 
> This is an update to the earlier frlock.
> 

Sorry, but I have lost track of what version is what.  Please
let me get my current act together and then prepare diffs
against (or new versions of) that.

You appear to have not noticed my earlier suggestions wrt
coding tweaks and inefficiencies in the new implementation.

- SEQ_INIT and seq_init can go away.

- do seq_write_begin/end need wmb(), or mb()?  Probably, we
  should just remove these functions altogether.

-
	+static inline int seq_read_end(const seqcounter_t *s, unsigned iv)
	+{
	+       mb();
	+       return (s->counter != iv) || (iv & 1);
	+}

  So the barriers changed _again_!  Could we please at least
  get Richard Henderson and Andrea to agree that this is the
  right way to do it?

-
	+typedef struct {
	+       volatile unsigned counter;
	+} seqcounter_t;

  Why did this become a struct?

  Why is it volatile?
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