[Lustre-devel] Needed: insight on obd_set_info_async()

[Andreas Dilger <adilger@sun.com>]

On Oct 04, 2009  12:11 -0500, Nicolas Williams wrote:
> On Sun, Oct 04, 2009 at 01:34:27AM -0600, Andreas Dilger wrote:
> > On Oct 02, 2009  17:06 -0500, Nicolas Williams wrote:
> > > I'm trying to find out which uses of obd_set_info_async() involve values
> > > that come from a PTLRPC message buffer, and which ones don't.  It would
> > > help to know what obd_set_info_async() is for...  It seems it's a
> > > glorified ioctl()...
> > 
> > Sort of, yes, though I would characterize it more like a "get/set system
> > xattr".  It can get/set key,value pairs on a local or remote node.  The
> > "async" part means that the caller is the one in charge of handling waiting
> > for completion of the operation.  This is important when doing an operation
> > that may involve many OSTs, since we want the RPCs to happen in parallel
> > instead of in series.
> 
> But does it always go over the wire?  Is it always executed with a 'val'
> that came off the wire?

No, getinfo/setinfo also operate locally in many places.  The caller isn't
supposed to know at what lower layer the request will be processed.

In that regard, the early design goal of the Lustre stack was that it
has a single API throughout the stack and is transparent whether the
operations are happening on a local or remote node, but I wasn't at all
involved in the 2.0 development and that goal has fallen by the wayside.

> > > I'm tempted to augment it to always take a struct ptlrpc_request *req
> > > argument, so that req == NULL || val == NULL, and when req != NULL the
> > > value will be obtained using req_capsule_*_get().  Between that and
> > > enhancements to req_capsule_extend() and what not we might be able to
> > > ensure that 'val' is always swabbed by capsule code.
> > 
> > I can't comment on the HEAD capsule code, maybe someone else can...
> 
> That's OK, I can take care of the capsule conversion for this function.
> But I need to understand it and the contexts when it's called a bit
> better.
> 
> Nico
> -- 

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.