[PATCH] nvme: add DIX support for nvme-rdma

[Keith Busch]

On Mon, Aug 29, 2022 at 05:56:39PM +0300, Max Gurtovoy wrote:
> On 8/29/2022 4:16 PM, Chao Leng wrote:
> > On 2022/8/29 18:43, Max Gurtovoy wrote:
> > > On 8/29/2022 11:12 AM, Chao Leng wrote:
> > > 
> > > You can mention that also in iser, if supported, the default is to
> > > use IP_CHECKSUM for DIX and not CRC.
> > According to DIX define:DIX = IP_CHECKSUM.
> > To reduce CPU utilization, the end-to-end DIF for SCSI protocols is
> > DIX-DIF when supported by hardware.
> 
> From what I re-call DIX was protection between host_buff -> host_device and
> DIF was protection between host_device -> target_device.
> 
> If now its defined as DIX == IP_CHECKSUM and DIF == CRC please mention it
> somehow in the commit message.

Where is this coming from? The NVMe command set spec says this is the
difference between DIF and DIX:

  The primary difference between these two mechanisms is the location of the
  protection information. In DIF, the protection information is contiguous with
  the logical block data and creates an extended logical block, while in DIX,
  the protection information is stored in a separate buffer.

Regarding CRC vs IP Checksum, the spec also says this:

  In addition to a CRC-16, DIX also specifies an optional IP checksum that is
  not supported by the NVM Express interface.

So DIX support doesn't imply IP checksum. Even if the host device can support
it, the target device can not report it uses that guard type.