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Date:   Thu, 31 Oct 2019 14:39:21 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Charles Machalow <csm10495@gmail.com>
Cc:     linux-nvme@lists.infradead.org, marta.rybczynska@kalray.eu,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nvme: change nvme_passthru_cmd64's result field.
Message-ID: <20191031133921.GA4763@lst.de>
References: <20191031050338.12700-1-csm10495@gmail.com>
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On Wed, Oct 30, 2019 at 10:03:38PM -0700, Charles Machalow wrote:
> Changing nvme_passthru_cmd64's result field to be backwards compatible
> with the nvme_passthru_cmd/nvme_admin_cmd struct in terms of the result
> field. With this change the first 32 bits of result in either case
> point to CQE DW0. This allows userspace tools to use the new structure
> when using the old ADMIN/IO_CMD ioctls or new ADMIN/IO_CMD64 ioctls.

All that casting is a pretty bad idea.  please just add an explicit
reserved field before the result, and check that it always is zero
in the ioctl handler.