verity: short circuit once you hit a verified node

verity: short circuit once you hit a verified node

Since we set the VERIFIED bits top-down we can short circuit once
we hit a VERIFIED node.

BUG=9752
TEST=Ran tests in verity.git. Ran platform_DMVerityCorruption on H/W.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>;
kernel.git Review URL: http://codereview.chromium.org/6670008

TBRing because code has already been LGTMed and committed to kernel.git.

Change-Id: Ib8fe833668a62bdc21946e2b274f970b0955cd8c

TBR=wad@chromium.org,taysom@chromium.org,ups@chromium.org

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=f9d2bfb

[Paul T, 2011-03-23 17:19:28]

LGTM

http://codereview.chromium.org/6721017/diff/1/dm-bht.c
File dm-bht.c (right):

http://codereview.chromium.org/6721017/diff/1/dm-bht.c#newcode694
dm-bht.c:694: /* TODO(msb,wad): would be nice to avoid two atomic reads */
I'd like to understand this comment better. From what I understand, atomic read
is just a volatile read. So once the value is in cache, the second read should
be fast or is something else going on?

[Mandeep Singh Baines, 2011-03-23 20:12:33]

On 2011/03/23 17:19:28, Paul T wrote:
> LGTM
> 
> http://codereview.chromium.org/6721017/diff/1/dm-bht.c
> File dm-bht.c (right):
> 
> http://codereview.chromium.org/6721017/diff/1/dm-bht.c#newcode694
> dm-bht.c:694: /* TODO(msb,wad): would be nice to avoid two atomic reads */
> I'd like to understand this comment better. From what I understand, atomic
read
> is just a volatile read. So once the value is in cache, the second read should
> be fast or is something else going on?

You're correct. The purpose was more for code cleanup than for performance. Will
pointed out a simple way of only reading the state in one place. Since
implemented and committed.