linux-ext4 - Re: [PATCH 07/17] vfs: Introduce new helpers for syncing after writing to O_SYNC file or IS

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Date:	Sun, 30 Aug 2009 17:35:51 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	hch@....de, linux-fsdevel@...r.kernel.org,
	Evgeniy Polyakov <zbr@...emap.net>, ocfs2-devel@....oracle.com,
	Joel Becker <joel.becker@...cle.com>,
	Felix Blyakher <felixb@....com>, xfs@....sgi.com,
	Anton Altaparmakov <aia21@...tab.net>,
	linux-ntfs-dev@...ts.sourceforge.net,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 07/17] vfs: Introduce new helpers for syncing after writing to O_SYNC file or IS_SYNC inode

Christoph Hellwig wrote:
> int generic_write_sync(struct file *file, loff_t pos, loff_t count)
> {
> 	if (!(file->f_flags & O_SYNC) && !IS_SYNC(file->f_mapping->host))
> 		return 0;
> 	return vfs_fsync_range(file, file->f_path.dentry, pos,
> 			       pos + count - 1, 1);
> }
> 
> and we can look into replacing the datasync flag with something more
> meaningfull later through the whole fsync stack.

I like that.  It looks really clear and self-documenting, if
vfs_fsync_range does what it sounds like, which is a nice change.

If I've guessed right what that code does, proper O_RSYNC will be easy:

int generic_sync_before_read(struct file *file, loff_t pos, loff_t count)
{
	int is_sync = ((file->f_flags & O_SYNC)
		       || IS_SYNC(file->f_mapping->host));
	int is_dsync = is_sync || (file->f_flags & O_DSYNC);

	if (!is_dsync || !(file->f_flags & O_RSYNC))
		return 0;
	return vfs_fsync_range(file, file->f_ath.denty, pos,
			       pos + count - 1, is_sync);
}

(By the way, did I mention Irix has range-fsync and range-fdatasync
system calls too :-) (actually fcntls))

-- Jamie
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