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

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Date:   Mon, 4 Nov 2019 06:51:08 -0800
From:   Charles Machalow <csm10495@...il.com>
To:     Marta Rybczynska <mrybczyn@...ray.eu>
Cc:     Christoph Hellwig <hch@....de>,
        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.

For this one yes, UAPI size changes. Though I believe this IOCTL
hasn't been in a released Kernel yet (just RC). Technically it may be
changeable as a fix until the next Kernel is released. I do think its
a useful enough
change to warrant a late fix.

- Charlie Scott Machalow

On Mon, Nov 4, 2019 at 6:34 AM Marta Rybczynska <mrybczyn@...ray.eu> wrote:
>
>
>
> ----- 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