Not sure whether this is coreutils or kernel. Maybe both. A filesystem's device number such as reported by `stat` can be derived from major and minor of the underlying block device, e.g. xfs, or be allocated at mount time, e.g. btrfs. Even in the former case, the device number can change between restarts, e.g. when multiple dm-crypt devices are created in different order. Changing device numbers cause trouble for applications that use the device number to identify a filesystem across restarts, e.g. KDE's baloo file indexer.
A mount option to specify the device number would fix this trouble without requiring applications to move to alternative ways of identifying filesystems, e.g. based on UUIDs. This option could be general, i.e. the device number can be set for any filesystem, including those that normally derive it from major and minor of their block device(s). The implementation would probably be simplified if the specified device numbers must come from a reserved pool. Otherwise, care must be taken that the numbers do not collide with automatically assigned device numbers, including those allocated later. Replaces bug #53209 References: https://bugs.kde.org/show_bug.cgi?id=402154 https://bugs.kde.org/show_bug.cgi?id=404057 https://bugs.kde.org/show_bug.cgi?id=413694 https://unix.stackexchange.com/questions/345220/btrfs-how-to-get-real-device-id https://stackoverflow.com/questions/4309882/device-number-in-stat-command-output/4309947
