[openib-general] [PATCH] IB/documentation - add new file to Documentation/infiniband

[James Lentini]

On Fri, 10 Nov 2006, Ralph Campbell wrote:

> > > > > +  ib_reg_phys_mr()  This function returns a pointer to struct ib_mr.
> > > > > +  It takes an array of device DMA addresses and lengths which are used
> > > > > +  to describe the memory region.  These addresses are created by
> > > > > +  calling the mapping functions listed for ib_get_dma_mr().
> > > > 
> > > > The iova is an in/out parameter. I recommend including a description 
> > > > of how to initialize it:
> > > > 
> > > >  The 'iova' argument can be used by the caller to request an address 
> > > >  to associate with the first byte of the address region. Upon return, 
> > > >  the 'iova' argument is the ... <continue with below>
> > > 
> > > Iova was at one point in time an in/out parameter but was changed
> > > to be just an in parameter some time ago.
> > 
> > At what point was this changed?
> 
> Maybe a year ago. I tried to find it in the SVN log but
> didn't find which revision changed it.
> 
> > In the 1.2 IBTA spec, it is described as an in/out.
> > 
> > For mthca, the iova value is an input (see mthca_reg_phys_mr). 
> 
> The IBTA spec. wasn't changed.
> The open-fabrics code was changed since none of the HCAs
> returned a modified iova value.  

Where did this change? All the versions of include/rdma/ib_verbs.h 
(kernel 2.6.18, svn, Roland's git) define ib_reg_phys_mr() as

struct ib_mr *ib_reg_phys_mr(struct ib_pd *pd,
                             struct ib_phys_buf *phys_buf_array,
                             int num_phys_buf,
                             int mr_access_flags,
                             u64 *iova_start)

indicating to me that iova_start is an in/out parameter.

> Also, there are currently no callers of ib_reg_phys_mr() that I know 
> of.

The NFS-RDMA client calls ib_reg_phys_mr() in certain configurations. 
See the code at http://www.sourceforge.net/projects/nfs-rdma.