[Xen-devel] [PATCH] docs: add misc/qemu-backends.txt

[Juergen Gross <jgross@xxxxxxxx>]

Document the interface between qemu and libxl regarding backends
supported by qemu.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 docs/misc/qemu-backends.txt | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 docs/misc/qemu-backends.txt

diff --git a/docs/misc/qemu-backends.txt b/docs/misc/qemu-backends.txt
new file mode 100644
index 0000000..f28755e
--- /dev/null
+++ b/docs/misc/qemu-backends.txt
@@ -0,0 +1,19 @@
+In order to know whether qemu supports a specific backend type libxl
+needs a way to obtain this information.
+
+As each qemu instance owns a path (named "<qemu>" from now on) in
+Xenstore the backend information is presented there. <qemu> is built
+from the domain id where the qemu instance is running <backend-dom>
+and the domain id of the target domain of the qemu process <domid>:
+
+<qemu> = /local/domain/<backend-dom>/device-model/<domid>
+
+Before signalling qemu is running by writing "running" to <qemu>/state
+qemu will create a Xenstore node for each supported backend under
+<qemu>/backends with the backend type as name (e.g.
+<qemu>/backends/qdisk for the qdisk backend).
+
+libxl can assume a backend of a specific type <type> is supported if:
+- <qemu>/backends/<type> is existing in Xenstore
+- or <qemu>/backends is not existing and <type> is one of:
+  "console", "vkbd", "vfb", "qdisk", "qnic"
-- 
2.6.6


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