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Date:   Mon, 22 May 2023 09:16:54 +0900
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Subject: Re: [PATCH 10/13] fs: factor out a direct_write_fallback helper
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To:     Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Xiubo Li <xiubli@redhat.com>,
        Ilya Dryomov <idryomov@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-block@vger.kernel.org, ceph-devel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
        "open list:F2FS FILE SYSTEM" <linux-f2fs-devel@lists.sourceforge.net>,
        cluster-devel@redhat.com, linux-xfs@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-mm@kvack.org
References: <20230519093521.133226-1-hch@lst.de>
 <20230519093521.133226-11-hch@lst.de>
From:   Damien Le Moal <dlemoal@kernel.org>
Organization: Western Digital Research
In-Reply-To: <20230519093521.133226-11-hch@lst.de>
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On 5/19/23 18:35, Christoph Hellwig wrote:
> Add a helper dealing with handling the syncing of a buffered write fallback
> for direct I/O.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks OK. One comment below.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

> +	/*
> +	 * We need to ensure that the page cache pages are written to disk and
> +	 * invalidated to preserve the expected O_DIRECT semantics.
> +	 */
> +	end = pos + buffered_written - 1;
> +	err = filemap_write_and_wait_range(mapping, pos, end);
> +	if (err < 0) {
> +		/*
> +		 * We don't know how much we wrote, so just return the number of
> +		 * bytes which were direct-written
> +		 */
> +		return err;
> +	}
> +	invalidate_mapping_pages(mapping, pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
> +	return direct_written + buffered_written;

Why not adding here something like:

	if (buffered_written != iov_iter_count(from))
		return -EIO;

	return direct_written + buffered_written;

to have the same semantic as plain DIO ?

-- 
Damien Le Moal
Western Digital Research