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Date:   Wed, 5 Sep 2018 23:13:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
        Stephen Bates <sbates@raithlin.com>,
        Keith Busch <keith.busch@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Dan Williams <dan.j.williams@intel.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and
 check support for requests
Message-ID: <20180905211351.GA2927@lst.de>
References: <20180905195647.GA1626@lst.de> <bcc1b3cf-2fd9-fa61-9cfb-b0e4d84e5d94@kernel.dk> <20180905201152.GA1893@lst.de> <eb42fb94-9da6-955b-8524-0a0f5ac4bd19@deltatee.com> <2a3394bd-5f13-4818-43f4-dfc61f501e05@kernel.dk> <e3ef26e6-6c8d-25b8-fa64-14594a51263c@deltatee.com> <3af4d1d4-da07-c0a6-8464-9ddc1378f2f4@kernel.dk> <f9e660cd-b597-bb6e-56a2-82fe71cb3649@deltatee.com> <34d9b2f7-9e6d-4a0a-77e5-ec0e99610f5c@kernel.dk> <c41c802c-9235-5383-2dfa-af9c1553f11b@deltatee.com>
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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.