multiple containerd options

Signed-off-by: Avi Deitcher <avi@deitcher.net>

Author: deitch

docs/faq.md

@@ -6,7 +6,7 @@ Please open an issue if you want to add a question here.
 
 LinuxKit does not require being installed on a disk, it is often run from an ISO, PXE or other
 such means, so it does not require an on disk upgrade method such as the ChromeOS code that
-is often used. It would definitely be possible to use that type of upgrade method if the 
+is often used. It would definitely be possible to use that type of upgrade method if the
 system is installed, and it would be useful to support this for that use case, and an
 updater container to control this for people who want to use this.
 
@@ -37,18 +37,41 @@ If you're not seeing `containerd` logs in the console during boot, make sure tha
 
 `init` and other processes like `containerd` will use the last defined console in the kernel `cmdline`. When using `qemu`, to see the console you need to list `ttyS0` as the last console to properly see the output.
 
-## Enabling debug or trace log levels on containerd
+## Enabling and controlling containerd logs
 
-On startup, linuxkit looks for and parses a file `/etc/containerd/cli-opts`. If it exists, the content is used as arguments to containerd. Thus, to enable
+On startup, linuxkit looks for and parses a file `/etc/containerd/runtime-config.toml`. If it exists, the content is used to configure containerd runtime.
+
+Sample config is below:
+
+```toml
+cliopts="--log-level debug"
+stderr="/var/log/containerd.out.log"
+stdout="stdout"
+```
+
+The options are as follows:
+
+* `cliopts`: options to pass to the containerd command-line as is.
+* `stderr`: where to send stderr from containerd. If blank, it sends it to the default stderr, which is the console.
+* `stdout`: where to send stdout from containerd. If blank, it sends it to the default stdout, which is the console. containerd normally does not have any stdout.
+
+The `stderr` and `stdout` options can take exactly one of the following options:
+
+* `stderr` - send to stderr
+* `stdout` - send to stdout
+* any absolute path (beginning with `/`) - send to that file. If the file exists, append to it; if not, create it and append to it.
+
+Thus, to enable
 a higher log level, for example `debug`, create a file whose contents are `--log-level debug` and place it on the image:
 
 ```yml
 files:
-  - path: /etc/containerd/cli-opts
-    contents: "--log-level debug"
+  - path: /etc/containerd/runtime-config.toml
+    source: "/path/to/runtime-config.toml"
+    mode: "0644"
 ```
 
-Note that the package that parses the contents splits on _all_ whitespace. It does not, as of this writing, support shell-like parsing, so the following will work:
+Note that the package that parses the `cliopts` splits on _all_ whitespace. It does not, as of this writing, support shell-like parsing, so the following will work:
 
 ```
 --log-level debug --arg abcd

pkg/init/cmd/service/system_init.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -14,12 +15,13 @@ import (
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/errdefs"
+	"github.com/pelletier/go-toml"
 	"github.com/pkg/errors"
 	log "github.com/sirupsen/logrus"
 )
 
 const (
-	containerdOptsFile = "/etc/containerd/cli-opts"
+	containerdOptsFile = "/etc/containerd/runtime-config.toml"
 )
 
 func cleanupTask(ctx context.Context, ctr containerd.Container) error {
@@ -85,14 +87,43 @@ func systemInitCmd(ctx context.Context, args []string) {
 
 	// look for containerd options
 	ctrdArgs := []string{}
+	var (
+		stderr io.Writer = os.Stderr
+		stdout io.Writer = os.Stdout
+	)
 	if b, err := ioutil.ReadFile(containerdOptsFile); err == nil {
-		ctrdArgs = strings.Fields(string(b))
+		config, err := toml.LoadBytes(b)
+		if err != nil {
+			log.Fatalf("error reading toml file %s: %v", containerdOptsFile, err)
+		}
+		if config != nil {
+			// did we have any CLI opts?
+			cliOptsLine := config.Get("cliopts")
+			if cliOptsLine != nil {
+				ctrdArgs = strings.Fields(cliOptsLine.(string))
+			}
+			// stderr?
+			stderrLine := config.Get("stderr")
+			if stderrLine != nil {
+				stderr, err = getWriter(stderrLine.(string))
+				if err != nil {
+					log.Fatal(err)
+				}
+			}
+			stdoutLine := config.Get("stdout")
+			if stdoutLine != nil {
+				stdout, err = getWriter(stdoutLine.(string))
+				if err != nil {
+					log.Fatal(err)
+				}
+			}
+		}
 	}
 
 	// start up containerd
 	cmd := exec.Command(*binary, ctrdArgs...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
 	if err := cmd.Start(); err != nil {
 		log.WithError(err).Fatal("cannot start containerd")
 	}
@@ -155,3 +186,21 @@ func systemInitCmd(ctx context.Context, args []string) {
 		}
 	}
 }
+
+func getWriter(line string) (io.Writer, error) {
+	switch {
+	case line == "stderr":
+		return os.Stderr, nil
+	case line == "stdout":
+		return os.Stdout, nil
+	case strings.HasPrefix(line, "/"):
+		// does the file exist?
+		f, err := os.OpenFile(line,
+			os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+		if err != nil {
+			return nil, fmt.Errorf("unable to open file %s for creation or appending: %v", line, err)
+		}
+		return f, nil
+	}
+	return nil, fmt.Errorf("invalid option for writer: %s", line)
+}

pkg/init/cmd/service/vendor.conf

@@ -1,2 +1,3 @@
 github.com/vishvananda/netlink f5a6f697a596c788d474984a38a0ac4ba0719e93
 github.com/vishvananda/netns 86bef332bfc3b59b7624a600bd53009ce91a9829
+github.com/pelletier/go-toml 5b4e7e5dcc567bbc53b25ad81e06493ede66d301