s390x: Dump storage keys qmp command

Provide a dump-skeys qmp command to allow the end user to dump storage
keys. This is useful for debugging problems with guest storage key support
within Qemu and for guest operating system developers.

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

qmp-commands.hx

@@ -870,6 +870,31 @@ Example:
 <- { "return": { "formats":
                     ["elf", "kdump-zlib", "kdump-lzo", "kdump-snappy"] }
 
+EQMP
+
+#if defined TARGET_S390X
+    {
+        .name       = "dump-skeys",
+        .args_type  = "filename:F",
+        .mhandler.cmd_new = qmp_marshal_input_dump_skeys,
+    },
+#endif
+
+SQMP
+dump-skeys
+----------
+
+Save guest storage keys to file.
+
+Arguments:
+
+- "filename": file path (json-string)
+
+Example:
+
+-> { "execute": "dump-skeys", "arguments": { "filename": "/tmp/skeys" } }
+<- { "return": {} }
+
 EQMP
 
     {