linux-kernel - Re: Initramfs FSID altered in 3.14

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Date:	Thu, 3 Apr 2014 15:13:07 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Dave Reisner <d@...conindy.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	thomas@...hlinux.org, P@...igbrady.com,
	alexandre.f.demers@...il.com
Subject: Re: Initramfs FSID altered in 3.14

Hello, Dave.

On Thu, Apr 03, 2014 at 01:57:44PM -0400, Dave Reisner wrote:
> With Linux 3.14, you might notice in /proc/self/mountinfo that your
> root's parent FSID is now 0, instead of the 1 that it's been for the
> last N years. Tejun wrote the change (9e30cc9595303b27b48) that caused
> this, but the change comes in a rather innocuous way. Instead of an
> internal kernel mount of sysfs being assigned 0, it's now the initramfs.
> 
> So far, this has already caused switch_root and findmnt (from
> util-linux) to break, cp (from coreutils) to break when using the -x
> flag in early userspace, and it's also been pointed out that systemd's
> readahead code makes assumptions about a device number of 0.
> 
> Are we now supposed to go and change all the assumptions in userspace
> about 0 being special? I'm conflicted. The kernel isn't supposed to
> break userspace, but it seems to me that FSIDs were never something to
> rely on -- similar to the block device numbering scheme.

I think this is the same problem Alexandre Demers reported.  Arch was
failing to boot with the commit.  There's already a patch pending to
reinstate the internal mount but I think what Thomas is proposing -
just starting allocating FSID from 1 is a better solution.  Alexandre,
can you please test Thomas' patch?

Thanks.

-- 
tejun
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