Add MemInfo to the system pkg.

MemInfo provides a simple API to get memory information from the
system.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

system/meminfo_linux.go

@@ -0,0 +1,67 @@
+package system
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/docker/docker/pkg/units"
+)
+
+var (
+	ErrMalformed = errors.New("malformed file")
+)
+
+// Retrieve memory statistics of the host system and parse them into a MemInfo
+// type.
+func ReadMemInfo() (*MemInfo, error) {
+	file, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	return parseMemInfo(file)
+}
+
+func parseMemInfo(reader io.Reader) (*MemInfo, error) {
+	meminfo := &MemInfo{}
+	scanner := bufio.NewScanner(reader)
+	for scanner.Scan() {
+		// Expected format: ["MemTotal:", "1234", "kB"]
+		parts := strings.Fields(scanner.Text())
+
+		// Sanity checks: Skip malformed entries.
+		if len(parts) < 3 || parts[2] != "kB" {
+			continue
+		}
+
+		// Convert to bytes.
+		size, err := strconv.Atoi(parts[1])
+		if err != nil {
+			continue
+		}
+		bytes := int64(size) * units.KiB
+
+		switch parts[0] {
+		case "MemTotal:":
+			meminfo.MemTotal = bytes
+		case "MemFree:":
+			meminfo.MemFree = bytes
+		case "SwapTotal:":
+			meminfo.SwapTotal = bytes
+		case "SwapFree:":
+			meminfo.SwapFree = bytes
+		}
+
+	}
+
+	// Handle errors that may have occurred during the reading of the file.
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	return meminfo, nil
+}