UMview: View-OS implemented as a System Call Virtual Machine

One component of the Virtual Square framework[12, 3, 4], is View-OS. Traditional OS’s implement the global view assumption: any two processes running on a computer share the same view of their execution environment. This “global” view includes the meaning of pathnames, network stacks, routing rules, devices etc. While processes may have different permissions to access these resources, the naming scheme is the same. View-OS removes the global view assumption. Each process in View-OS has its own view of the execution environment, i.e. its own view of the networking system, file systems, existing devices, inter-process communication, etc. Furthermore, process view redefinition in View-OS can be selectively applied to specific portions of a processes’ view: e.g. a process can change its view of the file system, or only on a subtree of the file system. UMview is a user-mode implementation of key View-OS concepts as a partial, modular, system call virtual machine (SCVM). A SCVM is a process-virtual machine[10, 11] where processes run natively on the processor and just the system calls are virtualized. User-Mode Linux (UML)[5, 6], whose virtual monitor is an entire linux kernel loaded as a process, is the canonical example of a SCVM. UMview is a partial SCVM since it is possible to provide a process with a view which is a mix of virtual and native entities. For example, UMview supports the mounting of a virtual filesystem. Afterwards, the processes’ view of the filesystem is composed of a virtual subtree rooted at the mountpoint, in addition to the pre-existing filesystem. Unlike traditional kernel mounts, UMview mount effects are limited to the processes running in the virtual machine. Furthermore, view modification actions, like the mount operation example, can be nested. UMview is a modular SCVM. Loadable modules provide suitable abstractions for supporting specific virtualizations: e.g. file systems, devices, networking systems, etc. UMview provides a flexible and general purpose support for virtualization. Using the View-OS concepts implemented as UMview modules one can “unify” several pre-existing models of virtualization.