From: Keith Busch <kbusch@kernel.org>
To: Charles Machalow <csm10495@gmail.com>
Cc: linux-nvme@lists.infradead.org
Subject: Re: nvme_passthru_cmd64 has a 4 byte hole
Date: Wed, 30 Oct 2019 15:32:33 +0900 [thread overview]
Message-ID: <20191030063233.GA16863@redsun51.ssa.fujisawa.hgst.com> (raw)
In-Reply-To: <CANSCoS8HakAy6zHgEjDiYQ87z83RJy-OC9ZfktRJwr+9kgnFKw@mail.gmail.com>
On Tue, Oct 29, 2019 at 09:43:20PM -0700, Charles Machalow wrote:
> Hey all,
>
> I noticed (via some debug) that nvme_passthru_cmd64 seems to have a 4
> byte hole that isn't currently accounted for in the struct:
> From pahole:
>
> struct nvme_passthru_cmd64 {
> __u8 opcode; /* 0 1 */
> __u8 flags; /* 1 1 */
> __u16 rsvd1; /* 2 2 */
> __u32 nsid; /* 4 4 */
> __u32 cdw2; /* 8 4 */
> __u32 cdw3; /* 12 4 */
> __u64 metadata; /* 16 8 */
> __u64 addr; /* 24 8 */
> __u32 metadata_len; /* 32 4 */
> __u32 data_len; /* 36 4 */
> __u32 cdw10; /* 40 4 */
> __u32 cdw11; /* 44 4 */
> __u32 cdw12; /* 48 4 */
> __u32 cdw13; /* 52 4 */
> __u32 cdw14; /* 56 4 */
> __u32 cdw15; /* 60 4 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> __u32 timeout_ms; /* 64 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> __u64 result; /* 72 8 */
>
> /* size: 80, cachelines: 2, members: 18 */
> /* sum members: 76, holes: 1, sum holes: 4 */
> /* last cacheline: 16 bytes */
> };
>
> (Since I doubt we can functionally change the structure at this
> point...)
Well, there is no official kernel release using this structure,
so I suppose even this late in the rc cycle, we can change it with
appropriate justification. I think an alternative to padding is to make
this a __u32[2] field, which should also be backward compatible with
the 4 byte result passthrough.
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next prev parent reply other threads:[~2019-10-30 6:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 4:43 nvme_passthru_cmd64 has a 4 byte hole Charles Machalow
2019-10-30 6:32 ` Keith Busch [this message]
2019-10-30 14:08 ` Charles Machalow
2019-10-31 2:56 ` Charles Machalow
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