Linux - couldn't mount RDWR because of unsupported optional features (400)

Question

I try to run Android from SD-card. This card is prepared. There are partitions: boot(FAT32), rootfs(ext4), system(ext4), cache(ext4) and usedata(ext4). Boot partitions has files to run u-boot: MLO, u-boot.bin and uImage. To run it I use commands

mmcinit 0
fatload mmc 0 0x80000000 uImage
setenv bootargs 'console=ttyO2,115200n8 mem=456M@0x80000000 mem=512M@0xA0000000 init=/init vram=10M omapfb.vram=0:4M androidboot.console=ttyO2 root=/dev/mmcblk1p2 rw rootwait rootfstype=ext4'
bootm 0x80000000

Than I see how Linux starts. But after few seconds on step of loading rootfs I see an error message

[    4.015655] EXT4-fs (mmcblk1p2): couldn't mount RDWR because of unsupported optional features (400)
[    4.036499] sd 0:0:0:0: [sda] Attached SCSI removable disk
[    4.079986] List of all partitions:
[    4.083801] b300        31162368 mmcblk0  driver: mmcblk
[    4.089660]   b301             128 mmcblk0p1 f9f21f00-a8d4-5f0e-9746-594869aec34e
[    4.097839]   b302             256 mmcblk0p2 f9f21f01-a8d4-5f0e-9746-594869aec34e
[    4.106018]   b303             128 mmcblk0p3 f9f21f02-a8d4-5f0e-9746-594869aec34e
[    4.114288]   b304           16384 mmcblk0p4 f9f21f03-a8d4-5f0e-9746-594869aec34e
[    4.122436]   b305              16 mmcblk0p5 f9f21f04-a8d4-5f0e-9746-594869aec34e
[    4.130676]   b306            8192 mmcblk0p6 f9f21f05-a8d4-5f0e-9746-594869aec34e
[    4.138916]   b307            8192 mmcblk0p7 f9f21f06-a8d4-5f0e-9746-594869aec34e
[    4.147094]   103:00000     524288 mmcblk0p8 f9f21f07-a8d4-5f0e-9746-594869aec34e
[    4.155334]   103:00001     262144 mmcblk0p9 f9f21f08-a8d4-5f0e-9746-594869aec34e
[    4.163574]   103:00002   30342128 mmcblk0p10 f9f21f09-a8d4-5f0e-9746-594869aec34e
[    4.171874] b310            2048 mmcblk0boot1  (driver?)
[    4.177734] b308            2048 mmcblk0boot0  (driver?)
[    4.183593] b318        15179776 mmcblk1  driver: mmcblk
[    4.189453]   b319          102400 mmcblk1p1 00000000-0000-0000-0000-000000000000
[    4.197692]   b31a           10240 mmcblk1p2 00000000-0000-0000-0000-000000000000
[    4.205932]   b31b               1 mmcblk1p3 00000000-0000-0000-0000-000000000000
[    4.214141]   b31d          262144 mmcblk1p5 00000000-0000-0000-0000-000000000000
[    4.222351]   b31e        13228032 mmcblk1p6 00000000-0000-0000-0000-000000000000
[    4.230682]   b31f         1572864 mmcblk1p7 00000000-0000-0000-0000-000000000000
[    4.238891] No filesystem could mount root, tried:  ext4
[    4.244812] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,26)
[    4.254089] CPU1: stopping

I don't know why it happens. How can I solve this problem?

Answer 1

The ext4 feature (400) is the new metadata_csum feature. If this feature is enabled and old tools are used to mount the filesystem they will only be able to mount read-only.

https://ext4.wiki.kernel.org/index.php/Ext4_Metadata_Checksums

To create a ext4 filesystem without this feature:

sudo mke2fs /dev/sdb1 -O ^metadata_csum

Or turn it off on an already created filesystem:

sudo tune2fs -O ^metadata_csum /dev/sdb1

Answer 2

The error "EXT4-fs : couldn't mount RDWR because of unsupported optional features (400)" is due to different versions between the partition formatter (mkfs.ext4) and the mounter.

You have two options:

a) Either you have to upgrade the mounter program using a newer distro inside the SD-card.

b) or you have to backup the files, reformat the SD-card with the same distro (the same ext4 versions) you are doing the mounting, and after the reformat copy the files again to the SD-card.

In the second option, care must be taken with the original ext4 options the formatter has put, trying to consider the same options at reformat. Note also that a reformat of partitions doesn't need a repartition of the whole device, so the boot MBR would not be altered.