[$] A new API for mounting filesystems

The mount()system call suffers from a number of different shortcomings that has ledsome to consider a different API. At last year's Linux Storage,Filesystem, and Memory-Management Summit (LSFMM), that someone wasMiklos Szeredi, who led a session to discuss hisideas for a new filesystem mounting API. Since then, David Howells has beenworking with Szeredi and VFS maintainer Al Viro on this API; at the 2018LSFMM, he presented that work.