Improving zvol support

[Andriy Gapon]

on 30/08/2013 17:22 Steven Hartland said the following:
> There's a few outstanding PR's for zvol issues such as:-
> http://www.freebsd.org/cgi/query-pr.cgi?pr=178999
> 
> I've attached a patch to this PR (also to this email)
> which helps clear quite a few issues highlighted by this
> PR and by tests in STF.
> 
> The locking side of this patch while not 100% ideal does
> prevent the common issues such as zvol renames so I think
> worth getting this committing until more time can be spent
> on it.
> 
> What do people think?

A few general comments:
- it's a good idea to describe the changes and possibly to provide a patch per
problem
- this looks like an svn diff output, for reviewers' convenience please use -x
-p options
- both I and Spectra Logic have independent patches to zvol code that
significantly change locking in it and completely remove spa_namespace_lock problem

I have never seen the Spectra's code although I did have a chance.  Will Andrews
convinced me that their approach is superior to mine and they were willing to
upstream their changes.  I think that it would be a good idea to take a look at
all proposed approaches, select or fuse the best and finally commit something.

BTW, the current zvol code has another major GEOM-related bug - it drops and
picks up g_topology_lock in zvol_geom_access, which must not be done.

P.S. message-id of my proposal is <510E9FFC.6000303 at FreeBSD.org>, it was posted
to this list.

-- 
Andriy Gapon