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From:   Charles Machalow <csm10495@gmail.com>
Date:   Thu, 31 Oct 2019 06:59:10 -0700
Message-ID: <CANSCoS-RzcutTWHN1t1iyW3GjqNcY5xFUZtJhAThDp5SPPrDAA@mail.gmail.com>
Subject: Re: [PATCH] nvme: change nvme_passthru_cmd64's result field.
To:     Christoph Hellwig <hch@lst.de>
Cc:     linux-nvme@lists.infradead.org, marta.rybczynska@kalray.eu,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
        Sagi Grimberg <sagi@grimberg.me>, linux-kernel@vger.kernel.org
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On Thu, Oct 31, 2019, 6:39 AM Christoph Hellwig <hch@lst.de> wrote

> 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.

Not quite sure what you mean by check for zero in the ioctl handler. I
like the idea of being able to use the same struct for either the
original or 64 ioctls from userspace. I don't believe adding the
explicit rsvd field allows that

- Charlie Scott Machalow

On Thu, Oct 31, 2019 at 6:39 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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.