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Date:   Mon, 4 Nov 2019 15:34:40 +0100 (CET)
From:   Marta Rybczynska <mrybczyn@kalray.eu>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Charles Machalow <csm10495@gmail.com>,
        linux-nvme <linux-nvme@lists.infradead.org>,
        kbusch <kbusch@kernel.org>, axboe <axboe@fb.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        linux-kernel <linux-kernel@vger.kernel.org>
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In-Reply-To: <20191031133921.GA4763@lst.de>
References: <20191031050338.12700-1-csm10495@gmail.com> <20191031133921.GA4763@lst.de>
Subject: Re: [PATCH] nvme: change nvme_passthru_cmd64's result field.
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Thread-Topic: nvme: change nvme_passthru_cmd64's result field.
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----- On 31 Oct, 2019, at 14:39, 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.

That would change the size of a structure in UAPI, won't it? 
I wanted to avoid it when adding the *64 ioctls and that's why
I added separate ones instead of extending the ones that exist.

Marta