linux-kernel - Re: [dm-devel] [PATCH v11 2/9] block: Add copy offload support infrastructure

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Date:   Mon, 29 May 2023 22:06:13 +0530
From:   Nitesh Shetty <nitheshshetty@...il.com>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Nitesh Shetty <nj.shetty@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-block@...r.kernel.org, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-mm@...ck.org,
        gost.dev@...sung.com, anuj20.g@...sung.com,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        ming.lei@...hat.com, James.Bottomley@...senpartnership.com,
        linux-fsdevel@...r.kernel.org, dlemoal@...nel.org,
        joshi.k@...sung.com, bvanassche@....org
Subject: Re: [dm-devel] [PATCH v11 2/9] block: Add copy offload support infrastructure

> > +/*
> > + * @bdev_in: source block device
> > + * @pos_in:  source offset
> > + * @bdev_out:        destination block device
> > + * @pos_out: destination offset
> > + * @len:     length in bytes to be copied
> > + * @endio:   endio function to be called on completion of copy operation,
> > + *           for synchronous operation this should be NULL
> > + * @private: endio function will be called with this private data, should be
> > + *           NULL, if operation is synchronous in nature
> > + * @gfp_mask:   memory allocation flags (for bio_alloc)
> > + *
> > + * Returns the length of bytes copied or error if encountered
> > + *
> > + * Description:
> > + *   Copy source offset from source block device to destination block
> > + *   device. Max total length of copy is limited to MAX_COPY_TOTAL_LENGTH
> > + */
> > +int blkdev_issue_copy(struct block_device *bdev_in, loff_t pos_in,
>
> I'd have thought you'd return ssize_t here.  If the two block devices
> are loopmounted xfs files, we can certainly reflink "copy" more than 2GB
> at a time.
>
> --D
>

Sure we will add this to make API future proof, but at present we do have
a limit for copy. COPY_MAX_BYTES(=128MB) at present. This limit is based
on our internal testing, we have plans to increase/remove with this
limit in future phases.

Thank you,
Nitesh Shetty