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Date: Mon, 12 May 2014 14:50:27 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Fabian Frederick <fabf@skynet.be>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, jack <jack@suse.cz>,
        hch <hch@infradead.org>, Viro <viro@zeniv.linux.org.uk>,
        tytso <tytso@mit.edu>
Subject: Re: [PATCH V5 1/2] FS: Add generic data flush to fsync
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On Mon, 12 May 2014 07:20:27 +0200 Fabian Frederick <fabf@skynet.be> wrote:

> This patch issues a flush in generic_file_fsync.
> (Modern filesystems already do it)
> 
> Behaviour can be reversed using /sys/devices/.../cache_type
> or by calling __generic_file_fsync

Well OK, but why?  What effect does the patch have?  Does it make the
kernel better and if so, how?

>
> +/**
> + * generic_file_fsync - generic fsync implementation for simple filesystems
> + *			with flush
> + * @file:	file to synchronize
> + * @start:	start offset in bytes
> + * @end:	end offset in bytes (inclusive)
> + * @datasync:	only synchronize essential metadata if true
> + *
> + */
> +
> +int generic_file_fsync(struct file *file, loff_t start, loff_t end,
> +		       int datasync)
> +{
> +	struct inode *inode = file->f_mapping->host;
> +	int err;
> +
> +	err = __generic_file_fsync(file, start, end, datasync);
> +	if (err)
> +		return err;
> +
> +	return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> +
> +}

Documentation/SubmitChecklist, section 2b ;)