linux-kernel - Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

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Message-ID: <481AFBC8.9050602@isomerica.net>
Date:	Fri, 02 May 2008 07:32:24 -0400
From:	Dan Noé <dpn@...merica.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Lothar Waßmann <LW@...O-electronics.de>,
	linux-kernel@...r.kernel.org
Subject: Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount
 point inside a read only filesystem

Andrew Morton wrote:
>> |root@...ton1:/# mount
>> |rootfs on / type rootfs (rw)
>> |/dev/root on / type jffs2 (ro)
>> |proc on /proc type proc (rw)
>> |sysfs on /sys type sysfs (rw)
>> |/dev/root on /dev/.static/dev type jffs2 (ro)
>> |tmpfs on /dev type tmpfs (rw,size=10240k,mode=755)
>> |tmpfs on /var type tmpfs (rw)
>> |tmpfs on /tmp type tmpfs (rw)
>> |devpts on /dev/pts type devpts (rw,gid=5,mode=620)
>> |tmpfs on /dev/shm type tmpfs (rw)
>> |root@...ton1:/# mkdir -p /dev/.udev/db
>> |mkdir: Cannot create directory `/dev/': Read-only file system
>>
>> While:
>> |root@...ton1:/# cd /dev
>> |root@...ton1:/# mkdir -p .udev/db
>> works as expected...
>>
>> Has anyone else encountered this problem already?
>> I've searched the archives but could not find anything related to this
>> problem.
> 
> I had a shot at scripting this, but for me, everything works OK.
> 
> #!/bin/sh
> dd if=/dev/zero of=file1 bs=1M count=32
> dd if=/dev/zero of=file2 bs=1M count=32
> yes | mkfs -t ext2 file1
> yes | mkfs -t ext2 file2
> mkdir -p mountpoint
> mount -o loop file1 mountpoint
> mkdir mountpoint/dir
> umount mountpoint
> mount -o loop,ro file1 mountpoint
> mount -o loop file2 mountpoint/dir
> mkdir -p $(/bin/pwd)/mountpoint/dir/subdir

Hmmm.  The thing you are doing differently is that the reporter's root 
filesystem is mounted read only but in your case (and the quick try I 
had at it) the read only file system is mounted below root.

However, I tried reproducing that scenario with a chroot and I still 
couldn't get it to happen.  No time to try a real root mount ro this 
morning but perhaps others can.

Cheers,
Dan

-- 
                     /--------------- - -  -  -   -   -
                     |  Dan Noé
                     |  http://isomerica.net/~dpn/
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