Re: [PATCH v3 2/2][BNX2]: Add iSCSI support to BNX2 devices.

On Tue, 25 Sep 2007 10:39:17 +0200
Hannes Reinecke [off-list ref] wrote:

Hi Tomo,

FUJITA Tomonori wrote:

quoted

On Sat, 8 Sep 2007 13:00:36 +0100
Christoph Hellwig [off-list ref] wrote:

quoted

On Sat, Sep 08, 2007 at 07:32:27AM -0400, Jeff Garzik wrote:

quoted

FUJITA Tomonori wrote:

quoted

Yeah, iommu code ignores the lld limitations (the problem is that the
lld limitations are in request_queue and iommu code can't access to
request_queue). There is no way to tell iommu code about the lld
limitations.

This fact very much wants fixing.

Absolutely.  Unfortunately everyone wastes their time on creating workarounds
instead of fixing the underlying problem.

Any ideas on how to fix this?

I chatted to Jens and James on this last week.

- we could just copies the lld limitations to device structure. it's
hacky but device structure already has hacky stuff.

- we could just link device structure to request_queue structure so
that iommu code can see request_queue structure.

- we could remove the lld limitations in request_queue strucutre and
have a new strucutre (something like struct io_restrictions). then
somehow we could link the new structure with request_queue and device
strucutres.

I'd prefer the latter. These struct io_restrictions could then be used
by dm (which has it's own version right now) to merge queue capabilities.

Yeah, we could nicely handle lld's restrictions (especially with
stacking devices). But iommu code needs only max_segment_size and
seg_boundary_mask, right? If so, the first simple approach to add two
values to device structure is not so bad, I think.