Add a basic README

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>

diff --git a/README b/README
new file mode 100644 (file)
index 0000000..4916a4a
--- /dev/null
+++ b/README
@@ -0,0 +1,24 @@
+Xen PassThrough Emulator
+------------------------
+
+This code is a small standalone device emulator for Xen that passes through
+a single type 0 PCI function.
+
+It needs to be built against the tools libraries of whichever version of
+Xen you wish to use. It requires libxenctrl, libxenevtchn,
+libxenforeignmemory and libxendevicemodel. It needs to be run as root, in
+a Linux domain 0 as it uses sysfs to interact with the PCI function being
+passed through.
+
+To use it, start a guest in the paused state and then start xenpt from a
+shell prompt... E.g.:
+
+sudo ./xenpt --domain 1 --host-sbdf 0000:05:00.0 --guest-sbdf 0000:00:0b.0
+
+This will pass through device 0 on bus 5, manifesting as device 11 on
+slot 0 in the guest. (Guests only have a single bus so make sure the
+guest bus number is 0).
+
+NOTE: Don't kill xenpt until after the guest has shut down. There is also
+      currently an undiagnosed issue where the domain remains in a zombie
+      state.