From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/4] fs: split update_time() into update_time() and
	write_time()
Date: Mon, 24 Nov 2014 07:21:01 -0800
Message-ID: <20141124152101.GA12575@infradead.org>
References: <1416599964-21892-1-git-send-email-tytso@mit.edu>
	<1416599964-21892-2-git-send-email-tytso@mit.edu>
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Cc: linux-fsdevel@vger.kernel.org,
	Ext4 Developers List <linux-ext4@vger.kernel.org>,
	linux-btrfs@vger.kernel.org, xfs@oss.sgi.com
To: Theodore Ts'o <tytso@mit.edu>
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On Fri, Nov 21, 2014 at 02:59:21PM -0500, Theodore Ts'o wrote:
> We needed to preserve update_time() because btrfs wants to have a
> special btrfs_root_readonly() check; otherwise we could drop the
> update_time() inode operation entirely.

Can't btrfs just set the immutable flag on every inode that is read
when the root has the BTRFS_ROOT_SUBVOL_RDONLY flag?  That would
cut down the places that need this check to the ioctl path so that
we prevent users from clearling the immutable flag.

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