The Design and Implementation of the Anykernel and Rump Kernels

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Figure 3.33: Remote client architecture. Remote clients communicate with
the rump kernel through the rumpclient library. The client and rump kernel may
or may not reside on the same host.
run and exit independently. This independence makes it straightforward to adapt
existing programs as rump kernel clients, and as we will see later in this section,
allows existing binaries to use services from a rump kernel without recomplication.
For example, it is possible to configure an unmodified Firefox browser to use a
TCP/IP stack provided by a rump kernel.
The general architecture of remote rump clients is illustrated in Figure 3.33. It is
explained in detail in the following sections.
Communication is done using host sockets. Currently, two protocol families can
be used for client-server communication: Unix domain sockets and TCP/IP. The
advantages of Unix domain sockets are that the available namespace is virtually
unlimited and it is easy to bind a private server in a local directory without fear of
a resource conflict. Also, it is possible to use host credentials (via chmod) to control
who has access to the server. The TCP method does not have these advantages —
in the general case it is not possible to guarantee that a predefined port is not in use
— but TCP does work over the Internet. Generally speaking, Unix domain sockets
should be used when the server and client reside on the same host.