linux-kernel - Re: "r/o bind mounts" patch in 2.6.26-rc6 changes (breaks?) error behaviour

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Date:	Fri, 20 Jun 2008 08:28:09 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Jens Rottmann <JRottmann@...PERTEmbedded.de>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: "r/o bind mounts" patch in 2.6.26-rc6 changes (breaks?) error
	behaviour

On Fri, 2008-06-20 at 07:17 -0700, Dave Hansen wrote:
> On Fri, 2008-06-20 at 12:16 +0200, Jens Rottmann wrote:
> > 
> > I noticed the following change in the error behaviour when attempting
> > to delete nonexisting files/dirs from R/O-mounted directories:
> > 
> > Linux 2.6.25.7:
> > rm /RO_mounted_path/nonexisting_file
> > ==> "No such file or directory"
> > 
> > Linux 2.6.26-rc6-git6:
> > rm /RO_mounted_path/nonexisting_file
> > ==> "Read-only file system"
> 
> We looked at this way back in the beginning when I started to work on
> the patches.  It was decided that the error codes weren't horribly
> important.  We did have a case a bit ago where it really mattered, and
> Al fixed that up.
> 
> I know this changed behavior a bit, but userspace can surely work around
> it with read-only operations (stat) when it is really important to get
> the error to the user just right.

Also, there are some nice benefits to the new way of doing it.  To
figure out if there is a file in that location also requires a path
walk.  Now, that isn't the most expensive thing in the world, but it is
a heck of a lot more expensive than just doing a read-only look at a
variable in the mount (in mnt_want_write()).

Don't you *want* warnings when an 'rm -f' runs into a r/o filesystem? ;)

-- Dave

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