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Date:   Mon, 20 Jul 2020 18:09:45 +0200
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <wqu@suse.com>
Cc:     linux-btrfs@vger.kernel.org, Christian Zangl <coralllama@gmail.com>
Subject: Re: [PATCH 1/2] btrfs-progs: convert: Prevent bit overflow for
 cctx->total_bytes
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On Mon, Jul 20, 2020 at 08:51:08PM +0800, Qu Wenruo wrote:
> --- a/convert/source-ext2.c
> +++ b/convert/source-ext2.c
> @@ -87,7 +87,8 @@ static int ext2_open_fs(struct btrfs_convert_context *cctx, const char *name)
>  	cctx->fs_data = ext2_fs;
>  	cctx->blocksize = ext2_fs->blocksize;
>  	cctx->block_count = ext2_fs->super->s_blocks_count;
> -	cctx->total_bytes = ext2_fs->blocksize * ext2_fs->super->s_blocks_count;
> +	cctx->total_bytes = (u64)ext2_fs->blocksize *
> +			    (u64)ext2_fs->super->s_blocks_count;

Do you need to cast both? Once one of the types is wide enough for the
result, there should be no loss.