linux-kernel - Re: [PATCH v6 2/4] Add support for SCT Write Same

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Message-ID: <CAJVOszDOPpMZgooKHc9+Tnjyd6a+sbMCJb0xeLyAD5n1vLT8nw@mail.gmail.com>
Date:   Thu, 25 Aug 2016 02:31:22 -0500
From:   Shaun Tancheff <shaun.tancheff@...gate.com>
To:     Tom Yan <tom.ty89@...il.com>
Cc:     Shaun Tancheff <shaun@...cheff.com>, linux-ide@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Hellwig <hch@....de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Damien Le Moal <damien.lemoal@...t.com>,
        Hannes Reinecke <hare@...e.de>,
        Josh Bingaman <josh.bingaman@...gate.com>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH v6 2/4] Add support for SCT Write Same

On Thu, Aug 25, 2016 at 1:23 AM, Tom Yan <tom.ty89@...il.com> wrote:
> You only fill the bytes that you want to to set explicitly:
>
> +       put_unaligned_le16(0x0002,  &sctpg[0]); /* SCT_ACT_WRITE_SAME */
> +       put_unaligned_le16(0x0101,  &sctpg[1]); /* WRITE PTRN FG */
> +       put_unaligned_le64(lba,     &sctpg[2]);
> +       put_unaligned_le64(num,     &sctpg[6]);
> +       put_unaligned_le32(0u,      &sctpg[10]);
>
> What I doubted is, if you don't memset (zero-fill) the buffer first,
> will other bytes have indeterministic value that causes random
> unexpected behavior?

No.
If there is random or unexpected behaviour the device is broken
and some other remedy, such as blacklisting, is required.

---
Shaun