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Date:   Mon, 2 Nov 2020 16:03:29 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <wqu@suse.com>
Cc:     linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: fix build warning due to u64 devided by u32 for
 32bit arch
Message-ID: <20201102150329.GC6756@twin.jikos.cz>
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On Mon, Nov 02, 2020 at 03:31:14PM +0800, Qu Wenruo wrote:
> [BUG]
> When building the kernel with subpage preparation patches, 32bit arches
> will complain about the following linking error:
> 
>    ld: fs/btrfs/extent_io.o: in function `release_extent_buffer':
>    fs/btrfs/extent_io.c:5340: undefined reference to `__udivdi3'
> 
> [CAUSE]
> For 32bits, dividing u64 with u32 need to call div_u64(), not directly
> call u64 / u32.
> 
> [FIX]
> Instead of calling the div_u64() macros, here we introduce a helper,
> btrfs_sector_shift(), to calculate the sector shift, and we just do bit
> shift to avoid executing the expensive division instruction.

I've refreshed and pushed the series adding fs_info::sectorsize_bits so
you can use it for the subpage patches.