Add logging project

Adds a logging daemon that collects logs in a ring buffer in a runc container.
The tools logwrite and logread can be used to read/write logs. The logging
daemon can be sent open file descriptors that will be read and included
in the logs.

Modifies init to start the daemon and use logwrite to capture logs from runc.

Signed-off-by: Magnus Skjegstad <magnus@skjegstad.com>

projects/logging/pkg/memlogd/cmd/logwrite/main.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+func getLogFileSocketPair() (*os.File, int) {
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	localFd := fds[0]
+	remoteFd := fds[1]
+
+	localLogFile := os.NewFile(uintptr(localFd), "")
+	return localLogFile, remoteFd
+}
+
+func sendFD(conn *net.UnixConn, remoteAddr *net.UnixAddr, source string, fd int) error {
+	oobs := syscall.UnixRights(fd)
+	_, _, err := conn.WriteMsgUnix([]byte(source), oobs, remoteAddr)
+	return err
+}
+
+func main() {
+	var err error
+	var ok bool
+
+	var serverSocket string
+	var name string
+
+	flag.StringVar(&serverSocket, "socket", "/tmp/memlogd.sock", "socket to pass fd's to memlogd")
+	flag.StringVar(&name, "n", "", "name of sender, defaults to first argument if left blank")
+	flag.Parse()
+	args := flag.Args()
+
+	if len(args) < 1 {
+		log.Fatal("no command specified")
+	}
+
+	if name == "" {
+		name = args[0]
+	}
+
+	localStdoutLog, remoteStdoutFd := getLogFileSocketPair()
+	localStderrLog, remoteStderrFd := getLogFileSocketPair()
+
+	var outSocket int
+	if outSocket, err = syscall.Socket(syscall.AF_UNIX, syscall.SOCK_DGRAM, 0); err != nil {
+		log.Fatal("Unable to create socket: ", err)
+	}
+
+	var outFile net.Conn
+	if outFile, err = net.FileConn(os.NewFile(uintptr(outSocket), "")); err != nil {
+		log.Fatal(err)
+	}
+
+	var conn *net.UnixConn
+	if conn, ok = outFile.(*net.UnixConn); !ok {
+		log.Fatal("Internal error, invalid cast.")
+	}
+
+	raddr := net.UnixAddr{Name: serverSocket, Net: "unixgram"}
+
+	if err = sendFD(conn, &raddr, name+".stdout", remoteStdoutFd); err != nil {
+		log.Fatal("fd stdout send failed: ", err)
+	}
+
+	if err = sendFD(conn, &raddr, name+".stderr", remoteStderrFd); err != nil {
+		log.Fatal("fd stderr send failed: ", err)
+	}
+
+	cmd := exec.Command(args[0], args[1:]...)
+	outStderr := io.MultiWriter(localStderrLog, os.Stderr)
+	outStdout := io.MultiWriter(localStdoutLog, os.Stdout)
+	cmd.Stderr = outStderr
+	cmd.Stdout = outStdout
+	if err = cmd.Run(); err != nil {
+		if exitError, ok := err.(*exec.ExitError); ok {
+			// exit with exit code from process
+			status := exitError.Sys().(syscall.WaitStatus)
+			os.Exit(status.ExitStatus())
+		} else {
+			// no exit code, report error and exit 1
+			fmt.Println(err)
+			os.Exit(1)
+		}
+	}
+}