linux-ext4 - Re: EXT4-fs (mmcblk0p1): couldn't mount as ext3 due to feature incompatibilities

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Date:   Fri, 2 Mar 2018 15:20:22 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "lczerner@...hat.com" <lczerner@...hat.com>,
        "sandeen@...hat.com" <sandeen@...hat.com>
CC:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: EXT4-fs (mmcblk0p1): couldn't mount as ext3 due to feature
 incompatibilities

On Fri, 2018-03-02 at 08:42 -0600, Eric Sandeen wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> On 3/2/18 8:30 AM, Joakim Tjernlund wrote:
> > On Fri, 2018-03-02 at 13:56 +0100, Lukas Czerner wrote:
> > > 
> > > 
> > > On Thu, Mar 01, 2018 at 12:48:58PM +0000, Joakim Tjernlund wrote:
> > > > Could the above(for ext2 as well) be removed or changed to a non error msg ?
> > > > It looks like a serious error msg as is now.
> > > > 
> > > >  Jocke
> > > 
> > > You're trying to mount a file system with features that a kernel you're
> > > currently using can't recognize or is incompatible with. So no, the
> > > error can't be just removed, it's there to prevent any further damage.
> > 
> > Not quite, I have a ext4 FS and fstab looks:
> > LABEL=BOOT            /boot           auto            noatime         1 2
> > 
> > and then I always get this error as kernel tries ext3 first, reports a big fat error,
> > then kernel tries ext4 and succeeds. I think this should be allowed without having
> > an error msg printed.
> 
> Ah, that is much more useful context than the original short report.  ;)
> 
> ext3 is always going to print a message if mount fails for this reason; it
> has no idea that ext4 will be tried next, all it knows is that it was told
> to mount, and it can't.

But I don't hav ext3, only ext4 in kernel:
# CONFIG_EXT2_FS is not set
# CONFIG_EXT3_FS is not set
CONFIG_EXT4_FS=y

ext4 know's ext3 and complains as is today. In this config one should not have to see
this error.

> 
> This is how mount behaves when you specify 'auto':
> 
>               If  no  -t  option  is  given, or if the auto type is specified,
>               mount will try to guess the desired type.  Mount uses the  blkid
>               library  for guessing the filesystem type; if that does not turn
>               up anything that looks familiar, mount will try to read the file
>               /etc/filesystems, or, if that does not exist, /proc/filesystems.
>               All of the filesystem types listed there will be  tried,  except
>               for those that are labeled "nodev" (e.g., devpts, proc and nfs).
> 
> What does your blkid think /dev/mmcblk0p1 is?  If it thinks it's ext3, what
> version is your blkid utility (or its owner package?)
> 
> If you specify it as ext4 rather than auto in fstab, you won't have the problem.

yes, but I don't want to do that and I should not have to.

> 
> Another way to avoid this might be to put ext4 before ext3 in /etc/filesystems.
> 
> But I'd be curious to know if blkid thinks this is ext3, that may be a bug.

Nope, it is ext4:
blkid /dev/mmcblk0p1
/dev/mmcblk0p1: LABEL="BOOT" UUID="f0a6a649-ce97-4d82-b190-eb1fc3e348a2" TYPE="ext4" PARTLABEL="M-dM-0M-^@...M
-$M-^@...M-8M-^@...M-^TM-^@...M- M-^@...M-^@M-^@...M-^HM-^@...M-<M-^@...M-<M-^@...M-^PM-^@"
PARTUUID="d65a22c5-be4c-410b-ab6e-89d732edd569