Add suppport for retrieving machine name

This adds support for reading /etc/os-release, parsing out
OPENBMC_TARGET_MACHINE and returning this to the caller.

Change-Id: If2a419b9a77597686f5137efce97b1150142f181
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/machine_name.cpp b/machine_name.cpp
new file mode 100644
index 0000000..9fcbd10
--- /dev/null
+++ b/machine_name.cpp
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2020 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "machine_name.hpp"
+
+#include "errors.hpp"
+
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
+#include <optional>
+#include <string>
+
+namespace google
+{
+namespace ipmi
+{
+
+struct GetMachineNameRequest
+{
+    uint8_t subcommand;
+} __attribute__((packed));
+
+struct GetMachineNameReply
+{
+    uint8_t subcommand;
+    uint8_t machineNameLength;
+    uint8_t machineName[0];
+} __attribute__((packed));
+
+ipmi_ret_t getMachineName(const uint8_t* reqBuf, uint8_t* replyBuf,
+                          size_t* dataLen, HandlerInterface* handler)
+{
+    GetMachineNameRequest request;
+    if (*dataLen < sizeof(request))
+    {
+        std::fprintf(stderr, "Invalid command length: %zu\n", *dataLen);
+        return IPMI_CC_REQ_DATA_LEN_INVALID;
+    }
+    std::memcpy(&request, reqBuf, sizeof(request));
+
+    static std::optional<std::string> machineName;
+    if (!machineName)
+    {
+        try
+        {
+            machineName = handler->getMachineName();
+        }
+        catch (const IpmiException& e)
+        {
+            return e.getIpmiError();
+        }
+    }
+
+    GetMachineNameReply reply;
+    size_t len = sizeof(reply) + machineName->size();
+    if (len > MAX_IPMI_BUFFER)
+    {
+        std::fprintf(stderr, "Response would overflow response buffer\n");
+        return IPMI_CC_INVALID;
+    }
+    reply.subcommand = request.subcommand;
+    reply.machineNameLength = machineName->size();
+    std::memcpy(replyBuf, &reply, sizeof(reply));
+    std::memcpy(replyBuf + sizeof(reply), machineName->data(),
+                machineName->size());
+    (*dataLen) = len;
+    return IPMI_CC_OK;
+}
+
+} // namespace ipmi
+} // namespace google