Re: [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 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?
> 

scsi_do/wait_req could do the checking and submit mutliple requests for sg I
mean.