[openib-general] [kernel verbs] u64 vs dma_addr_t

[James Lentini]

On Fri, 30 Dec 2005, Caitlin Bestler wrote:

> openib-general-bounces at openib.org wrote:
> > sean> James Lentini wrote:
> > sean> > Why is the ib_sge's addr a u64 and not a dma_addr_t?
> > sean>
> > sean> It's the same address that the user can transfer to the remote
> > sean> side. 
> > 
> > It can be the same address, but does it have to be?
> > 
> > A user can directly map local addresses to InfiniBand I/O
> > virtual addresses, but I don't think it is a requirement. In
> > other words, I thought that user could register address x and
> > request an InfiniBand I/O virtual address of y, x != y, for
> > the mapping.
> > 
> > I understand why the ib_send_wr's rdma.remote_addr needs to
> > be a u64, since it ultimately winds up on the wire.
> > 
> > In the case of the ib_sge's addr, I didn't think these values
> > left the local node. My assumption (based on looking at the
> > mthca driver) is that they are supposed to contain "local"
> > I/O addresses (bus addresses). Therefore, my confusion over
> > why dma_addr_t wasn't used.
> 
> A privileged user, such as an NFS Daemon or iSER iSCSI Target, can 
> and will create Memory Regions that are not part of its own address 
> space out of page buffers. Even running on a 32-bit kernel it might 
> create a memory region larger than 2**32.
> 
> Admittedly, that isn't very likely unless it is the *only* daemon 
> running on the machine. But it is legal.

How does the size of a region relate to my original question on the 
type of an ib_sge.addr?