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

[James Lentini]

Replies below:

On Fri, 10 Nov 2006, Ralph Campbell wrote:

<snip>
> > > +  Remote processes should use the same address for 'remote_addr'
> > > +  as the local kernel's address as returned by the mapping functions
> > > +  listed above.  The only difference is the local kernel uses the
> > > +  'lkey' and the remote kernel uses the 'rkey'.
> > 
> > I found the above paragraph difficult to understand on the first 
> > read. How about structuring the text similar to the user space 
> > explanation above:
> > 
> >  The addresses returned by these mapping functions should be 
> >  used for a struct ib_send_wr's 'remote_addr' field with the 
> >  appropriate rkey.
> 
> OK.
> I guess I was trying to point out that the address used with the
> lkey or rkey will always be the same when accessing the same byte
> of memory. It is just that the lkey is used when accessing memory
> locally and the rkey is used to access the memory remotely.

That is a good way of looking at it.

<snip>
> > > +  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?

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). 

> I modified the text as follows:
> 
> The 'iova' argument can be used by the caller to set the address
> of the first byte of the address region.  The addresses used
> with struct ib_sge 'addr' and struct ib_send_wr 'remote_addr' are
> thus 'iova' plus offset within the length of the memory region.
> The 'lkey' and 'rkey' fields for the above structs should be set
> with the values returned in the struct ib_mr 'lkey' and 'rkey' fields.