From: hch@lst.de (Christoph Hellwig)
Subject: [PATCH] nvme: support bi-directional commands
Date: Wed, 7 Dec 2016 18:33:23 +0100 [thread overview]
Message-ID: <20161207173323.GA24967@lst.de> (raw)
In-Reply-To: <1481132364-20583-1-git-send-email-keith.busch@intel.com>
On Wed, Dec 07, 2016@12:39:24PM -0500, Keith Busch wrote:
> The nvme specification defines the opcode's lower 2 bits as the
> transfer direction, which allows for bi-directional commands. While
> there are no standard defined opcodes that use both data directions,
> this is something a vendor unique opcode may use.
>
> This patch adds support for bi-directional user commands. The block
> layer doesn't natively support a request with both directions, but we
> can treat it like a read and set up rq_map_data to force copying the
> user data to the kernel buffers before the transfer.
The block layer actually supports bidi commands for SCSI OSD devices
using two struct requests. But it's giant mess, and given that no
NVMe command in the spec requires it I am absoutely 100% against
supporting this in NVMe. It's just going to create a mess for everyone
involved, even worse so for fabrics.
Just don't do it.
next prev parent reply other threads:[~2016-12-07 17:33 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-07 17:39 [PATCH] nvme: support bi-directional commands Keith Busch
2016-12-07 17:33 ` Christoph Hellwig [this message]
2016-12-07 17:50 ` Keith Busch
2016-12-07 17:44 ` Christoph Hellwig
2016-12-07 18:07 ` Keith Busch
2016-12-07 17:59 ` Christoph Hellwig
2016-12-07 18:15 ` Keith Busch
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