linux-kernel - Re: [PATCH] nfs: Don't try mounting device as nfs root unless type fully matches

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Message-ID: <20120107181221.GA3777@umich.edu>
Date:	Sat, 7 Jan 2012 13:12:21 -0500
From:	Jim Rees <rees@...ch.edu>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Sasha Levin <levinsasha928@...il.com>, linux@...ik.name,
	Trond.Myklebust@...app.com, penberg@...nel.org,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfs: Don't try mounting device as nfs root unless type
 fully matches

Chuck Lever wrote:

  On Jan 7, 2012, at 4:12 AM, Sasha Levin wrote:
  
  > Currently, we'll try mounting any device who's major device number is
  > UNNAMED_MAJOR as NFS root. This would happen for non-NFS devices as well (such
  > as 9p devices) but it wouldn't cause any issues since mounting the device
  > as NFS would fail quickly and the code proceeded to doing the proper mount:
  > 
  > 	[  101.522716] VFS: Unable to mount root fs via NFS, trying floppy.
  > 	[  101.534499] VFS: Mounted root (9p filesystem) on device 0:18.
  > 
  > Commit 6829a048 ("NFS: Retry mounting NFSROOT") has introduced retries when
  > mounting NFS root, which means that now we don't immediately fail and instead
  > it takes an additional 90+ seconds until we stop retrying.
  > 
  > This meant that it would take an additional 90 seconds to boot when we're not
  > using a device type which gets detected in order before NFS.
  
  The long timeouts are kind of irrelevant, in my view.  The real problem is
  that NFS was tried at all in this case.  That behavior was not introduced
  by 6829a058.

The comment does imply that 6829a048 introduced a bug, but that's not true.
It uncovered a bug that was there before.

I would change the part about "now we don't immediately fail."  It didn't
immediately fail before, but the timeout was short enough that you wouldn't
notice it.
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