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Date: Thu, 09 Oct 2014 10:44:12 -0500
From: Eric Sandeen <sandeen@redhat.com>
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To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org
Subject: Re: What is the vision for btrfs fs repair?
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On 10/9/14 8:49 AM, Duncan wrote:
> Austin S Hemmelgarn posted on Thu, 09 Oct 2014 09:18:22 -0400 as
> excerpted:
> 
>> On 2014-10-09 08:34, Duncan wrote:
> 
>>> The only way a read-only
>>> mount should be writable is if it's mounted (bind-mounted or
>>> btrfs-subvolume-mounted) read-write elsewhere, and the write occurs to
>>> that mount, not the read-only mounted location.
> 
>> In theory yes, but there are caveats to this, namely:
>> * atime updates still happen unless you have mounted the fs with noatime

Getting off the topic a bit, but that really shouldn't happen:

#define IS_NOATIME(inode)       __IS_FLG(inode, MS_RDONLY|MS_NOATIME)

and in touch_atime():

        if (IS_NOATIME(inode))
                return;

-Eric