linux-ext4 - Re: [RFC PATCH 2/8] brd: use memcpy_from_page() in copy_from

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Date:   Sun, 7 Feb 2021 20:35:46 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Chaitanya Kulkarni <chaitanya.kulkarni@....com>
Cc:     linux-block@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, axboe@...nel.dk, tytso@....edu,
        adilger.kernel@...ger.ca, jaegeuk@...nel.org, chao@...nel.org,
        johannes.thumshirn@....com, damien.lemoal@....com,
        bvanassche@....org, dongli.zhang@...cle.com, clm@...com,
        dsterba@...e.com, ebiggers@...nel.org, hch@...radead.org,
        dave.hansen@...el.com
Subject: Re: [RFC PATCH 2/8] brd: use memcpy_from_page() in copy_from_brd()

On Sun, Feb 07, 2021 at 11:04:19AM -0800, Chaitanya Kulkarni wrote:
> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@....com>
> ---
>  drivers/block/brd.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index d41b7d489e9f..c1f6d768a1b3 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -220,7 +220,6 @@ static void copy_from_brd(void *dst, struct brd_device *brd,
>  			sector_t sector, size_t n)
>  {
>  	struct page *page;
> -	void *src;
>  	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
>  	size_t copy;
>  
> @@ -236,11 +235,9 @@ static void copy_from_brd(void *dst, struct brd_device *brd,
>  		sector += copy >> SECTOR_SHIFT;
>  		copy = n - copy;
>  		page = brd_lookup_page(brd, sector);
> -		if (page) {
> -			src = kmap_atomic(page);
> -			memcpy(dst, src, copy);
> -			kunmap_atomic(src);
> -		} else
> +		if (page)
> +			memcpy_from_page(dst, page, offset, copy);

Why 'offset'?

Ira

> +		else
>  			memset(dst, 0, copy);
>  	}
>  }
> -- 
> 2.22.1
>