osutil: add helper for getting the kernel command line

osutil/kcmdline.go

@@ -179,11 +179,11 @@ func KernelCommandLineSplit(s string) (out []string, err error) {
 // missing from the kernel command line or it has no value (eg. quiet), the key
 // is omitted from the returned map.
 func KernelCommandLineKeyValues(keys ...string) (map[string]string, error) {
-	buf, err := ioutil.ReadFile(procCmdline)
+	cmdline, err := KernelCommandLine()
 	if err != nil {
 		return nil, err
 	}
-	params, err := KernelCommandLineSplit(strings.TrimSpace(string(buf)))
+	params, err := KernelCommandLineSplit(cmdline)
 	if err != nil {
 		return nil, err
 	}
@@ -203,3 +203,12 @@ func KernelCommandLineKeyValues(keys ...string) (map[string]string, error) {
 	}
 	return m, nil
 }
+
+// KernelCommandLine returns the command line reported by the running kernel.
+func KernelCommandLine() (string, error) {
+	buf, err := ioutil.ReadFile(procCmdline)
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(buf)), nil
+}

osutil/kcmdline_test.go

@@ -191,3 +191,20 @@ func (s *kcmdlineTestSuite) TestGetKernelCommandLineKeyValue(c *C) {
 		}
 	}
 }
+
+func (s *kcmdlineTestSuite) TestKernelCommandLine(c *C) {
+	d := c.MkDir()
+	newProcCmdline := filepath.Join(d, "cmdline")
+	restore := osutil.MockProcCmdline(newProcCmdline)
+	defer restore()
+
+	cmd, err := osutil.KernelCommandLine()
+	c.Assert(err, ErrorMatches, `.*/cmdline: no such file or directory`)
+	c.Check(cmd, Equals, "")
+
+	err = ioutil.WriteFile(newProcCmdline, []byte("foo bar baz panic=-1\n"), 0644)
+	c.Assert(err, IsNil)
+	cmd, err = osutil.KernelCommandLine()
+	c.Assert(err, IsNil)
+	c.Check(cmd, Equals, "foo bar baz panic=-1")
+}