Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 31 insertions, 0 deletions

diff --git a/docs/specs/pci-testdev.txt b/docs/specs/pci-testdev.txt
new file mode 100644
index 000000000..4280a1e73
--- /dev/null
+++ b/docs/specs/pci-testdev.txt
@@ -0,0 +1,31 @@
+pci-test is a device used for testing low level IO
+
+device implements up to three BARs: BAR0, BAR1 and BAR2.
+Each of BAR 0+1 can be memory or IO. Guests must detect
+BAR types and act accordingly.
+
+BAR 0+1 size is up to 4K bytes each.
+BAR 0+1 starts with the following header:
+
+typedef struct PCITestDevHdr {
+    uint8_t test;  <- write-only, starts a given test number
+    uint8_t width_type; <- read-only, type and width of access for a given test.
+                           1,2,4 for byte,word or long write.
+                           any other value if test not supported on this BAR
+    uint8_t pad0[2];
+    uint32_t offset; <- read-only, offset in this BAR for a given test
+    uint32_t data;    <- read-only, data to use for a given test
+    uint32_t count;  <- for debugging. number of writes detected.
+    uint8_t name[]; <- for debugging. 0-terminated ASCII string.
+} PCITestDevHdr;
+
+All registers are little endian.
+
+device is expected to always implement tests 0 to N on each BAR, and to add new
+tests with higher numbers.  In this way a guest can scan test numbers until it
+detects an access type that it does not support on this BAR, then stop.
+
+BAR2 is a 64bit memory bar, without backing storage.  It is disabled
+by default and can be enabled using the membar=<size> property.  This
+can be used to test whether guests handle pci bars of a specific
+(possibly quite large) size correctly.