linux-kernel - Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests

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Date:   Wed, 5 Sep 2018 23:13:51 +0200
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and
 check support for requests

On Wed, Sep 05, 2018 at 03:03:18PM -0600, Logan Gunthorpe wrote:
> There is no special p2p submission process. In the nvme-of case we are
> using the existing process and with the code in blk-core it didn't
> change it's process at all. Creating a helper will create one and I can
> look at making a pci_p2pdma_submit_bio() for v6; but if the developer
> screws up and still calls the regular submit_bio() things will only be
> very subtly broken and that won't be obvious.

I thought about that when reviewing the previous series, and even
started hacking it up.  In the end I decided against it for the above
reason - it just adds code, but doesn't actually help with anything
as it is trivial to forget, and not using it will in fact just work.