Re: Bug In ext4 in kernels > 2.6.39 - Not mounting with arguments/options I specify in fstab on root remount

[Matt Parnell <mparnell@gmail.com>]

On 10/22/2011 02:32 AM, Ted Ts'o wrote:
> On Sat, Oct 22, 2011 at 02:51:35AM -0500, Matt Parnell wrote:
>> That doesn't really help me at all, it's not
>> rootflags=data=writeback causing this, it's starting to make me
>> think that arch's init may be to blame, although I previously ruled
>> it out...
> Well, it looks like rootflags=data=writeback is not making it to the
> file system.  That's why it's not showing up in /proc/mounts, from you
> showed us.  Can you look at the kernel dmesg?
>
> You should see something like this:
>
> [    1.421146] EXT3-fs (vda): error: couldn't mount because of unsupported optional features (240)
> [    1.434057] EXT4-fs (vda): couldn't mount as ext2 due to feature incompatibilities
> [    1.454631] EXT4-fs (vda): mounted filesystem with writeback data mode. Opts: data=writeback
> [    1.455966] VFS: Mounted root (ext4 filesystem) readonly on device 254:0.
>
>
> The first line is the failure to mount the root file system as ext3.
> The 2nd is the failure to mount the file system as ext2, using the
> ext4 file system driver.  The last two lines show the options show the
> mount as ext4.
>
> What do those two lines look to you.  If you don't see "Opts:
> data=writeback", then somehow the rootflags option isn't getting passed
> down to the file system.  Then when you try to remount the file system
> read/write, the fact that you have "data=writeback" in your /etc/fstab
> causes the failure to remount.
>
> If you simply remove that from /etc/fstab, things should work better.
> The remount will preserve whatever data=journalling mode was in use
> when the root file system was originallymounted as.  If rootflags is
> non-functional, then the file system won't be mounted as
> data=writeback, but at least the boot sequence will continue without
> blowing out.
>
> 							- Ted
Looks like the kernel isn't creating the /dev/root link/block device, 
either all of the time or some of the time, I'm confused.