[$] Six (or seven) new system calls for filesystem mounting

Mounting filesystems is a complicated business. The kernel supports a widevariety of filesystem types, and each has its own, often extensive set of options. As a result, the mount()system call is complex, and the list of mountoptions is a rather long read. But even with all of that complexity,mount() does not do everything that users would like. Forexample, the options for a mount operation must all fit within a single4096-byte page - the fact that this is a problem for some users isillustrative in its own right. Theproblems with mount() have come up at various meetings, includingat the 2018 Linux Storage, Filesystem, andMemory-Management Summit. A setof patches implementing a new approach is getting closer to beingready, but it features some complexity of its own and there are someremaining concerns about the proposed system-call API.