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, 53 insertions, 0 deletions

diff --git a/docs/specs/vmcoreinfo.txt b/docs/specs/vmcoreinfo.txt
new file mode 100644
index 000000000..bcbca6fe4
--- /dev/null
+++ b/docs/specs/vmcoreinfo.txt
@@ -0,0 +1,53 @@
+=================
+VMCoreInfo device
+=================
+
+The `-device vmcoreinfo` will create a fw_cfg entry for a guest to
+store dump details.
+
+etc/vmcoreinfo
+**************
+
+A guest may use this fw_cfg entry to add information details to qemu
+dumps.
+
+The entry of 16 bytes has the following layout, in little-endian::
+
+#define VMCOREINFO_FORMAT_NONE 0x0
+#define VMCOREINFO_FORMAT_ELF 0x1
+
+    struct FWCfgVMCoreInfo {
+        uint16_t host_format;  /* formats host supports */
+        uint16_t guest_format; /* format guest supplies */
+        uint32_t size;         /* size of vmcoreinfo region */
+        uint64_t paddr;        /* physical address of vmcoreinfo region */
+    };
+
+Only full write (of 16 bytes) are considered valid for further
+processing of entry values.
+
+A write of 0 in guest_format will disable further processing of
+vmcoreinfo entry values & content.
+
+You may write a guest_format that is not supported by the host, in
+which case the entry data can be ignored by qemu (but you may still
+access it through a debugger, via vmcoreinfo_realize::vmcoreinfo_state).
+
+Format & content
+****************
+
+As of qemu 2.11, only VMCOREINFO_FORMAT_ELF is supported.
+
+The entry gives location and size of an ELF note that is appended in
+qemu dumps.
+
+The note format/class must be of the target bitness and the size must
+be less than 1Mb.
+
+If the ELF note name is "VMCOREINFO", it is expected to be the Linux
+vmcoreinfo note (see Documentation/ABI/testing/sysfs-kernel-vmcoreinfo
+in Linux source). In this case, qemu dump code will read the content
+as a key=value text file, looking for "NUMBER(phys_base)" key
+value. The value is expected to be more accurate than architecture
+guess of the value. This is useful for KASLR-enabled guest with
+ancient tools not handling the VMCOREINFO note.