[Ocfs2-devel] lvb length issue [was Re: [ocfs2-tools-devel] question of ocfs2_controld (Jun 27)]

[David Teigland <teigland@redhat.com>]

On Fri, Jul 31, 2009 at 07:59:08PM +0800, Coly Li wrote:
> 
> 
> David Teigland Wrote:
> > On Wed, Jul 08, 2009 at 09:15:42AM -0500, David Teigland wrote:
> >> On Tue, Jul 07, 2009 at 10:47:42AM -0700, Joel Becker wrote:
> >>> 	In this case, it's userspace utilities locking to verify no one
> >>> else is doing anything in the cluster.  coly has noticed mkfs.ocfs2, but
> >>> tunefs.ocfs2 and fsck.ocfs2 do the same thing.
> >>> 	While a 64byte user lvb would be ideal, I think a flag to work
> >>> around it would be great.  If the flag says "I know this lockspace may
> >>> have !32byte LVBs, but I promise not to use them", and you can error
> >>> when someone tries to set/get LVBs in that case, I think it works.
> > 
> > Here's a kernel patch that I've not yet tried.  The code using libdlm will
> > need to add the flag 0x00000010 to dlm_new_lockspace().  (Until we've added
> > the new LVB64 define to libdlm.h.)
> > 
> > +#define DLM_LSFL_LVB64		0x00000010
> >
> Another difficulty is user space libdlm interface. Right now, the interface
> mkfs.ocfs2 uses to create a lock space is,
> dlm_lshandle_t dlm_create_lockspace(const char *name, mode_t mode)
> {
>         return create_lockspace(name, mode, 0);
> }
> 
> There is no way to set flags in dlm_create_lockspace() and it is set to 0 inside
> the interface.
> 
> Is it possible to export create_lockspace() and release_lockspace() from libdlm
> ? So ocfs2-tools can load these symbols with dlopen() and calls these routines
> with flags (set DLM_LSFL_LVB64).
> 
> Other 2 options might be,
> 1) add flags in dlm_create_lockspace(), which will change libdlm api.
> 2) update default lvb length from 32bytes to 64bytes.

I don't think I'll bother with the LVB64 flag hack.  Instead, I'm planning to
do a larger API change to really support variable length lvb's from userspace.

It's actually dlm_new_lockspace() that you would use to pass flags, and once
we add variable length lvb's we'll need a new third call that adds an lvblen
parameter.

Dave