Is there a guarantee that if all data before the filesystem superblock is zero, and that the filesystem never writes to this region, libblkid (and thus, presumably, mount(8)) will always mount the filesystem with the correct filesystem type, even if e.g. someone writes a file containing a superblock of a different filesystem and the filesystem happens to put it where that superblock is valid? The motivation for this message is that systemd-gpt-generator generates mountpoints based on Discoverable Partition Specification GUIDs. These indicate the mountpoint of the partition but not the filesystem type. If a correctly-produced filesystem image will always continue to be recognized as the correct type, this is fine. Otherwise, an unlucky combination of writes to the filesystem and filesystem allocation decisions could cause the filesystem to start being mounted as the wrong type, which would be very bad. According to https://github.com/util-linux/util-linux/issues/1305, libblkid can indeed probe for subsequent superblocks after the first one it finds. -- Sincerely, Demi Marie Obenour (she/her/hers)
