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Date:   Tue, 28 Jun 2022 18:34:14 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     James Yonan <james@openvpn.net>
Cc:     linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] namei: implemented RENAME_NEWER flag for renameat2()
 conditional replace
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On Mon, Jun 27, 2022 at 04:11:07PM -0600, James Yonan wrote:

> 	    && d_is_positive(new_dentry)
> 	    && timespec64_compare(&d_backing_inode(old_dentry)->i_mtime,
> 				  &d_backing_inode(new_dentry)->i_mtime) <= 0)
> 		goto exit5;
> 
> It's pretty cool in a way that a new atomic file operation can even be
> implemented in just 5 lines of code, and it's thanks to the existing
> locking infrastructure around file rename/move that these operations
> become almost trivial.  Unfortunately, every fs must approve a new
> renameat2() flag, so it bloats the patch a bit.

How is it atomic and what's to stabilize ->i_mtime in that test?
Confused...