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

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Message-ID: <20191104150151.GA26808@redsun51.ssa.fujisawa.hgst.com>
Date:   Tue, 5 Nov 2019 00:01:51 +0900
From:   Keith Busch <kbusch@...nel.org>
To:     Marta Rybczynska <mrybczyn@...ray.eu>
Cc:     Charles Machalow <csm10495@...il.com>,
        Christoph Hellwig <hch@....de>,
        linux-nvme <linux-nvme@...ts.infradead.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 Mon, Nov 04, 2019 at 03:56:57PM +0100, Marta Rybczynska wrote:
> ----- On 4 Nov, 2019, at 15:51, Charles Machalow csm10495@...il.com wrote:
> 
> > 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.
> 
> The old one is in UAPI for years. The new one is not yet, right. I'm OK
> to change the new structure. To have compatibility you would have to use
> the new structure (at least its size) in the user space code. This is
> what you'd liek to do?

Charles is proposing only to modify the recently introduced 64-bit ioctl
struct without touching the existing 32 bit version. He just wanted the
lower 32-bits of the 64-bit result to occupy the same space as the 32-bit
ioctl's result. That space in the 64-bit version is currently occupied
by an implicit struct padding.