svn commit: r204470 - head/sys/fs/msdosfs

[Kostik Belousov]

On Sun, Feb 28, 2010 at 07:00:10PM +0100, Attilio Rao wrote:
> 2010/2/28 Konstantin Belousov <kib at freebsd.org>:
> > Author: kib
> > Date: Sun Feb 28 17:13:07 2010
> > New Revision: 204470
> > URL: http://svn.freebsd.org/changeset/base/204470
> >
> > Log:
> >  Add per-mountpoint lockmgr lock for msdosfs. It is intended to be used
> >  as fat bitmap lock and to replace global mutex protecting fileno rbtree.
> 
> Looking at this patch, it seems you can safely use a sx lock here and
> I would prefer that as we don't want to encourage more lockmgr to get
> in.
> If you are concerned about writer starvation in any way here,
> probabilly the right solution is to implement it in sx and remove
> lockmgr also from the export code.

There is no write starvation in the msdosfs case, because all locks
are acquired exclusively (this is not true for the export list locking,
and write starvation is real issue there).

I used lockmgr mostly because it is fs code.
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