libvchan-socket

This is a socket implementation of libvchan, analogous to the Xen one (https://github.com/QubesOS/qubes-core-vchan-xen/).

Compiling

make all
sudo make install

Usage

Use <libvchan.h> in your program. The API should be the same as Xen version.

Compile your program with:

gcc -c program.c `pkg-config --cflags vchan-socket`
gcc program.o -o program `pkg-config --libs`

The library will use Unix socket with the following path:

/var/run/vchan/vchan.<server_domain>.<client_domain>.<port>.sock

This is configurable:

• the local domain number is provided as VCHAN_DOMAIN environment variable (because it cannot be passed using the API),
• the default directory can be provided as VCHAN_SOCKET_DIR, which is useful if you don't want to run as root.

The server will accept connections at that path, and the client will try to connect (and reconnect). Only one connection at a time is supported.

Architecture

To (mostly) keep libvchan's semantics, libvchan-socket starts a separate thread responsible for connection management and socket I/O. Data is exchanged using a pair of ring buffers.

libvchan-socket-simple

libvchan-socket-simple is a simpler implementation that does not use a separate thread. It should be less error-prone, and make debugging (e.g. with strace) easier, but it has limitations that mean programs will need to be adapted:

• libvchan_buffer_space() doesn't tell you how much data you can write, it just returns 1 if you can write anything at all. That means you have to do the buffering yourself.

• Sending will always block if you are disconnected.

• libvchan_wait currently waits only for reads to unblock, now writes. Similarly, read events on libvchan_fd_for_select() will not tell you anything about writes.

Tests

See tests/ and run-tests script. The tests are written in Python and use cffi for interfacing with C code.