As of d77ccdc644a59b412d8e101576134c90a0aa6797, IMA will trigger a rehash of any file on a FUSE filesystem for every measurement. This has a significant impact on performance. Individual FUSE filesystems may have the ability to identify whether a file needs to be rehashed, and some may even have the ability to obtain the file hash out of band without needing the kernel to do it. Longer term, this may also be usable for other scenarios where a filesystem can provide a trustworthy hash (eg, fs-verity on ext4 could provide a hash and then later abort any read()s that discover that the file doesn't match the measurement).
