065ab4c470
The 'f' ioctls with numbers 19-26 decimal are currently used for fscrypt (a.k.a. ext4/f2fs/ubifs encryption), and up to 39 decimal is reserved for future fscrypt use, as per the comment in fs/ext4/ext4.h. So the reserved range is 13-27 hex. Document this in ioctl-number.rst. Signed-off-by: Eric Biggers <ebiggers@google.com>