MFC r236507, r237931, r238120, r238538:

MFC r236507, r237931, r238120, r238538:

r236507 (pjd):

Simplify the code by using snprlcat().

r237931 (pjd):

Check if there is cmsg at all.

r238120 (pjd):

Make use of GEOM Gate direct reads feature. This allows HAST to serve
reads with native speed of the underlying provider.
There are three situations when direct reads are not used:
1. Data is being synchronized and synchronization source is the secondary
   node, which means secondary node has more recent data and we should read
   from it.
2. Local read failed and we have to try to read from the secondary node.
3. Local component is unavailable and all I/O requests are served from the
   secondary node.

Sponsored by:	Panzura, http://www.panzura.com

r238538:

Metaflush on/off values don't need quotes.

Reviewed by:	pjd

git-svn-id: svn://svn.freebsd.org/base/stable/8@240270 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f