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From:   Nitesh Shetty <nitheshshetty@gmail.com>
Date:   Mon, 14 Aug 2023 22:31:53 +0530
Message-ID: <CAOSviJ2+tUZ=jiOnPSi8=mOzjANwvuNXAkAG6f3ADGi=M=F5PQ@mail.gmail.com>
Subject: Re: [dm-devel] [PATCH v14 03/11] block: add copy offload support
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Nitesh Shetty <nj.shetty@samsung.com>,
        Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com,
        Keith Busch <kbusch@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        martin.petersen@oracle.com, linux-doc@vger.kernel.org,
        gost.dev@samsung.com, Anuj Gupta <anuj20.g@samsung.com>,
        linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, mcgrof@kernel.org, dlemoal@kernel.org,
        linux-fsdevel@vger.kernel.org
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On Sat, Aug 12, 2023 at 3:10=E2=80=AFAM Bart Van Assche <bvanassche@acm.org=
> wrote:
>
> On 8/11/23 03:52, Nitesh Shetty wrote:
> > + * Description:
> > + *   Copy source offset to destination offset within block device, usi=
ng
> > + *   device's native copy offload feature.
>
> Offloading the copy operation is not guaranteed so I think that needs to
> be reflected in the above comment.
>
Acked.
> > + *   We perform copy operation by sending 2 bio's.
> > + *   1. We take a plug and send a REQ_OP_COPY_SRC bio along with sourc=
e
> > + *   sector and length. Once this bio reaches request layer, we form a
> > + *   request and wait for dst bio to arrive.
>
> What will happen if the queue depth of the request queue at the bottom
> is one?
>
For any reason if a request reaches the driver with only one of the src/dst=
 bio,
copy will fail. This design requires only one request to do a copy,
so it should work fine.

> > +             blk_start_plug(&plug);
> > +             dst_bio =3D blk_next_bio(src_bio, bdev, 0, REQ_OP_COPY_DS=
T, gfp);
>
> blk_next_bio() can return NULL so its return value should be checked.
>
Acked.

Thank you,
Nitesh Shetty