logcheck: docs update

Clarifications based on PR review of
kubernetes#297.

hack/tools/logcheck/README.md

@@ -25,8 +25,9 @@ via a configuration file. That file contains lines in this format:
 `<checks>` is a comma-separated list of the names of checks that get enabled or
 disabled when a file name matches the regular expression. A check gets disabled
 when its name has `-` as prefix and enabled when there is no prefix or `+` as
-prefix. All regular expressions are checked in order, so later lines can
-override the previous ones.
+prefix. Only checks that are mentioned explicitly are modified. All regular
+expressions are checked in order, so later lines can override the previous
+ones.
 
 In this example, checking for klog calls is enabled for all files under
 `pkg/scheduler` in the Kubernetes repo except for `scheduler.go`
@@ -42,31 +43,38 @@ the next section.
 
 # Checks
 
-## unstructured
+## unstructured (enabled by default)
 
 Unstructured klog logging calls are flagged as error.
 
-## klog
+## klog (disabled by default)
 
 None of the klog logging methods may be used. This is even stricter than
 `unstructured`. Instead, code should retrieve a logr.Logger from klog and log
 through that.
 
-## parameters
+## parameters (enabled by default)
 
-Key/value parameters for structured logging calls are checked:
+This ensures that if certain logging functions are allowed and are used, those
+functions are passed correct parameters.
+
+### all calls
+
+Format strings are not allowed where plain strings are expected.
+
+### structured logging calls
+
+Key/value parameters for logging calls are checked:
 - For each key there must be a value.
 - Keys must be constant strings.
 
 This also warns about code that is valid, for example code that collects
 key/value pairs in an `[]interface` variable before passing that on to a log
 call. Such valid code can use `nolint:logcheck` to disable the warning (when
-invoking logcheck through golangci-lint) or the check can be disabled for the
-file.
-
-In addition, format strings are not allowed as string parameters.
+invoking logcheck through golangci-lint) or the `parameters` check can be
+disabled for the file.
 
-## with-helpers
+## with-helpers (disabled by default)
 
 `logr.Logger.WithName`, `logr.Logger.WithValues` and `logr.NewContext` must not
 be used.  The corresponding helper calls from `k8s.io/klogr` should be used

hack/tools/logcheck/pkg/logcheck.go

@@ -93,7 +93,7 @@ klog methods (Info, Infof, Error, Errorf, Warningf, etc).`)
 
 	return &analysis.Analyzer{
 		Name: "logcheck",
-		Doc:  "Tool to check use of unstructured logging patterns.",
+		Doc:  "Tool to check logging calls.",
 		Run: func(pass *analysis.Pass) (interface{}, error) {
 			return run(pass, &c)
 		},