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From:   Yuxuan Shui <yshuiv7@gmail.com>
Date:   Tue, 25 Aug 2020 11:40:34 +0100
Message-ID: <CAGqt0zxoJZrYXS+wp7bwfsajfpaotu02oUy53VkQ5CTGcE_2hA@mail.gmail.com>
Subject: Re: [PATCH] iomap: iomap_bmap should accept unwritten maps
To:     Christoph Hellwig <hch@infradead.org>
Cc:     "Darrick J. Wong" <darrick.wong@oracle.com>,
        viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
        linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca
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Hi,

On Tue, Aug 25, 2020 at 11:20 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Tue, Aug 25, 2020 at 10:26:14AM +0100, Yuxuan Shui wrote:
> > Hi,
> >
> > Do we actually want to fix this bug or not? There are a number of
> > people actually seeing this bug.
>
> bmap should not succeed for unwritten extents.

Why not? Unwritten extents are still allocated extents.

>
> > If you think this is not the right fix, what do you think we should
> > do? If the correct fix is to make ext4 use iomap_swapfile_activate,
> > maybe we should CC the ext4 people too?
>
> Yes, ext4 should use iomap_swapfile_activate.

OK, let me CC the ext4 people.

Context:

https://bugzilla.kernel.org/show_bug.cgi?id=207585

> commit ac58e4fb03f9d111d733a4ad379d06eef3a24705 moved ext4_bmap from
> generic_block_bmap to iomap_bmap, this introduced a regression which
> prevents some user from using previously working swapfiles. The kernel
> will complain about holes while there are none.

> What is happening here is that the swapfile has unwritten mappings,
> which is rejected by iomap_bmap, but was accepted by ext4_get_block.

-- 

Regards
Yuxuan Shui