linux-ext4 - Re: [PATCH 1/3] vfs: Add page_cache_seek_hole

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Message-ID: <20170626104156.GA23149@infradead.org>
Date:   Mon, 26 Jun 2017 03:41:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 1/3] vfs: Add page_cache_seek_hole_data helper

On Fri, Jun 23, 2017 at 02:19:31AM +0200, Andreas Gruenbacher wrote:
> Both ext4 and xfs implement seeking for the next hole or piece of data
> in unwritten extents by scanning the page cache, and both versions share
> the same bug when iterating the buffers of a page: the start offset into
> the page isn't taken into account, so when a page fits more than two
> filesystem blocks, things will go wrong.  For example, on a filesystem
> with a block size of 1k, the following command will fail:
> 
>   xfs_io -f -c "falloc 0 4k" \
>             -c "pwrite 1k 1k" \
>             -c "pwrite 3k 1k" \
>             -c "seek -a -r 0" foo

Can you wire this up for xfstests, please?