On Tue, Jan 5, 2016 at 5:05 PM, Remi Locherer <remi.loche...@relo.ch> wrote: > Hi, > > I tried to mount an ext4 filesystem on OpenBSD which was created on > CentOS7. I get this: > > remi@mistral:~% doas mount -t ext2fs /dev/sd0m /mnt > mount_ext2fs: /dev/sd0m on /mnt: specified device does not match mounted > device > remi@mistral:~% dmesg | grep incomp > ext2fs: unsupported incompat features 0x2c2 > remi@mistral:~% > > Which feature is 0x2c2? Maybe I can disable this or re-create the filesystem > on Linux without this feature?
It's a bitmask combination of features, see https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#The_Super_Block (entry 0x60, s_feature_incompat). Features supported in OpenBSD are described in src/sys/ufs/ext2fs/ext2fs.h, specifically the #define EXT2F_INCOMPAT_SUPP bit. It appears that there is some read-only ext4 support in OpenBSD, but not for your particular FS -- yours contains the bit 0x80 (INCOMPAT_64BIT, not even listed in OpenBSD, let alone in EXT4F_RO_INCOMPAT_SUPP). If you want to share the FS read/write between OpenBSD and Linux, it's probably easier to create it as ext2 rather than tracking down which ext4 features to disable. -Andrew
