[PATCH 21.02 03/11] ramips: mt7621: Add support for ZyXEL NR7101

[Hauke Mehrtens]

On 6/8/21 1:10 PM, Bjørn Mork wrote:
> Tested-by: Bjørn Mork <bjorn at mork.no>
> 
> 
> Unrelated, but confused the hell out of me:
> 
> I tested this by sysupgrading from a master based installation using a
> 5.10 kernel.  And ended up with a tmpfs overlay because of:
> 
> [    9.833676] UBIFS (ubi0:1): Mounting in unauthenticated mode
> [    9.845003] UBIFS error (ubi0:1 pid 561): ubifs_mount: 'compressor "zstd" is not compiled in
> [    9.862780] mount_root: failed to mount -t ubifs /dev/ubi0_1 /tmp/overlay: No error information
> [    9.880490] mount_root: overlay filesystem has not been fully initialized yet
> [    9.895085] mount_root: switching to ubifs overlay
> [    9.904741] mount_root: switching to ubifs failed - fallback to ramoverlay
> 
> 
> So I reinstalled the 21.02 build by sysupgrading from the running 21.02,
> and everything was fine again - as expected.
> 
> I realize that I did this to myself, and that this sort of downgrade
> using sysupgrade is a pretty weird usecase.  But maybe there are other
> similar situations where we can end up with an unmountable UBIFS due to
> the missing compressor?
> 
> The problem seems to be as simple as CONFIG_UBIFS_FS_ZSTD being
> undefined in target/linux/generic/config-5.4 in 21.02.  It is defined
> for a number of targets, though. Just not ralink.
> 
> This was fixed in master by commit
> 
>    be7b56027899 ("kernel: enable lzo, zlib and zstd in ubifs").
> 
> Obvious candidate for backport to 21.02?

This problem should affect the following targets:
target/linux/apm821xx/nand
target/linux/ath79/mikrotik
target/linux/ath79/nand
target/linux/kirkwood
target/linux/lantiq/xway
target/linux/mediatek/mt7622
target/linux/mvebu
target/linux/oxnas/ox820
target/linux/ramips/mt7621
They all have CONFIG_UBIFS_FS set, but not CONFIG_UBIFS_FS_ZSTD.

OpenWrt 21.02 uses UBIFS_COMPR_LZO by default OpenWrt master uses 
UBIFS_COMPR_ZSTD by default.
Downgrading a OpenWrt 21.02 installation to 19.07 should work.

Did someone check how much bigger the images are getting with 
CONFIG_UBIFS_FS_ZSTD?

If they are not so much bigger I would suggest to add 
CONFIG_UBIFS_FS_ZSTD to OpenWrt 21.02 then the downgrade from master 
should work.

Hauke
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