[dm-devel] Re: [PATCH RFC 0/4] use scatter lists for all block pc requests and simplify hw handlers

[Michael Christie <michaelc cs wisc edu>]

Quoting James Bottomley <James Bottomley SteelEye com>:

> On Tue, 2005-06-07 at 13:10 +0100, Christoph Hellwig wrote:
> > shouldn't blk_rq_map_kern handle a 0 buffer and do nothing more than
> > blk_get_request?  It's not exactly a criticial fastpath and that would make
> life
> > easier for the callers.
> 
> Yes ... and it should probably do bio bouncing as well, since there's
> nothing special we have to do on completion to clean it up.

ok. I just made it like the existing blk_rq_map_user which made the caller do
those things.

> 
> I also think we might need a blk_rq_kern_iovec call that would take a
> vector of user I/O's and map it to a multiple bio request.  This would

Does it need to be a multiple bio request? A single bio should be able to handle
 a request's segments and sectors limits.
 
Will the user assure that the iovec will fit in a single request to handle a
case where the iovec is greater than the phys or hw segment limits though?