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Date: Tue, 3 Dec 2013 16:42:47 -0500
From: Rich Felker <>
Subject: Re: _PATH_LASTLOG

On Tue, Dec 03, 2013 at 01:00:26PM -0800, Nathan McSween wrote:
> You can implement this with bind mounts and containers as well, maybe 
> when Linux gets union mounts within the vfs this can be done cleanly 
> and per container.

I'm not holding my breath for union mounts. The likely candidate to go
in, overlayfs, has HORRIBLY WRONG semantics with respect to inodes and
file identity. For example if you have an open file descriptor to a
given file for read and another process opens the file for write, the
dev/inode changes and you don't see any of the changes in your
existing open file. It's as if open (for write) also performs unlink
and O_CREAT behind your back.

Making a union mount filesystem with proper semantics would require
some fairly heavy machinery to give consistent inode behavior.


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