linux-ext4 - Re: ext4 confusion

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Date:   Mon, 5 Mar 2018 22:40:04 -0600
From:   Eric Sandeen <sandeen@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-ext4@...r.kernel.org,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: ext4 confusion

On 3/5/18 10:38 PM, Randy Dunlap wrote:
> On 03/05/2018 08:34 PM, Eric Sandeen wrote:
>> On 3/5/18 10:17 PM, Randy Dunlap wrote:
>>> Hi,
>>>
>>> With the following kernel config entries on Linux 4.16-rc3:
>>>
>>> CONFIG_EXT2_FS=m
>>> # CONFIG_EXT2_FS_XATTR is not set
>>> CONFIG_EXT3_FS=m
>>> # CONFIG_EXT3_FS_POSIX_ACL is not set
>>> # CONFIG_EXT3_FS_SECURITY is not set
>>> CONFIG_EXT4_FS=y
>>> CONFIG_EXT4_FS_POSIX_ACL=y
>>> CONFIG_EXT4_FS_SECURITY=y
>>> # CONFIG_EXT4_ENCRYPTION is not set
>>> # CONFIG_EXT4_DEBUG is not set
>>> CONFIG_JBD2=y
>>> # CONFIG_JBD2_DEBUG is not set
>>>
>>> ext4_fill_super() tells me:
>>>
>>> [    3.033174] EXT4-fs (sda5): couldn't mount as ext3 due to feature incompatibilities
>>> [    3.100186] EXT4-fs (sda5): mounted filesystem with ordered data mode. Opts: (null)
>>> [    3.102683] VFS: Mounted root (ext4 filesystem) readonly on device 8:5.
>>>
>>>
>>> This is a new install, new filesystem. It has never been ext2 or ext3.
>>>
>>> After bootup and before I do anything else, I can remount /dev/sda5 on / as
>>> rw and everything is OK.
>>>
>>> What am I doing wrong?
>>
>> Hm you're the second person to report this in a week.  
>> (see EXT4-fs (mmcblk0p1): couldn't mount as ext3 due to feature incompatibilities)
>>
>> It sounds like filesystem probing behavior; it tried to mount as ext3 and failed
>> (as it should fail) then moved on to ext4 and succeeded.
> 
> Mostly succeeded, but why did it leave the filesystem as read-only?

oh it left it there?  Root usually mounts readonly then transitions to RW.
That didn't eventually happen?

> 
>> I sent:
>>
>> [PATCH V2] ext4: don't complain about incorrect features when probing
>>
>> which should fix it, but I really wonder why this is just now showing up for 
>> people; it could be a combination of /etc/filesystems, fstab entries, blkid
>> handling in mount, etc...
>>
>> Is this a new OS/installer release where this is showing up, or did a simple
>> kernel upgrade trigger it?  If the latter, what kernel version didn't have
>> the above kernel message?
> 
> It's a new OS/installer.  OpenSUSE Tumbleweed, which is their bleeding edge
> rolling updates release.

Hrmph.  A lot of things go into this behavior, it may not be a kernel change at
all that has made it show up now...

-Eric