linux-kernel - Re: [PATCH] nvme: change nvme_passthru

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Message-ID: <1977598237.90293761.1572878080625.JavaMail.zimbra@kalray.eu>
Date:   Mon, 4 Nov 2019 15:34:40 +0100 (CET)
From:   Marta Rybczynska <mrybczyn@...ray.eu>
To:     Christoph Hellwig <hch@....de>
Cc:     Charles Machalow <csm10495@...il.com>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        kbusch <kbusch@...nel.org>, axboe <axboe@...com>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvme: change nvme_passthru_cmd64's result field.



----- On 31 Oct, 2019, at 14:39, Christoph Hellwig hch@....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