Split HostUtil functionality into its own files

This patch takes all the HostUtil functionality currently found in
mount*.go files and copies it into hostutil*.go files. Care was taken to
preserve git history to the fullest extent.

As part of doing this, some common functionality was moved into
mount_helper files in preperation for HostUtils to stay in k/k and Mount
to move out. THe tests for each relevant function were moved to test
files to match the appropriate location.

pkg/util/mount/mount_helper_unix.go

@@ -19,8 +19,20 @@ limitations under the License.
 package mount
 
 import (
+	"fmt"
 	"os"
+	"strconv"
+	"strings"
 	"syscall"
+
+	utilio "k8s.io/utils/io"
+)
+
+const (
+	// At least number of fields per line in /proc/<pid>/mountinfo.
+	expectedAtLeastNumFieldsPerMountInfo = 10
+	// How many times to retry for a consistent read of /proc/mounts.
+	maxListTries = 3
 )
 
 // IsCorruptedMnt return true if err is about corrupted mount point
@@ -42,3 +54,80 @@ func IsCorruptedMnt(err error) bool {
 
 	return underlyingError == syscall.ENOTCONN || underlyingError == syscall.ESTALE || underlyingError == syscall.EIO || underlyingError == syscall.EACCES
 }
+
+// This represents a single line in /proc/<pid>/mountinfo.
+type mountInfo struct {
+	// Unique ID for the mount (maybe reused after umount).
+	id int
+	// The ID of the parent mount (or of self for the root of this mount namespace's mount tree).
+	parentID int
+	// The value of `st_dev` for files on this filesystem.
+	majorMinor string
+	// The pathname of the directory in the filesystem which forms the root of this mount.
+	root string
+	// Mount source, filesystem-specific information. e.g. device, tmpfs name.
+	source string
+	// Mount point, the pathname of the mount point.
+	mountPoint string
+	// Optional fieds, zero or more fields of the form "tag[:value]".
+	optionalFields []string
+	// The filesystem type in the form "type[.subtype]".
+	fsType string
+	// Per-mount options.
+	mountOptions []string
+	// Per-superblock options.
+	superOptions []string
+}
+
+// parseMountInfo parses /proc/xxx/mountinfo.
+func parseMountInfo(filename string) ([]mountInfo, error) {
+	content, err := utilio.ConsistentRead(filename, maxListTries)
+	if err != nil {
+		return []mountInfo{}, err
+	}
+	contentStr := string(content)
+	infos := []mountInfo{}
+
+	for _, line := range strings.Split(contentStr, "\n") {
+		if line == "" {
+			// the last split() item is empty string following the last \n
+			continue
+		}
+		// See `man proc` for authoritative description of format of the file.
+		fields := strings.Fields(line)
+		if len(fields) < expectedAtLeastNumFieldsPerMountInfo {
+			return nil, fmt.Errorf("wrong number of fields in (expected at least %d, got %d): %s", expectedAtLeastNumFieldsPerMountInfo, len(fields), line)
+		}
+		id, err := strconv.Atoi(fields[0])
+		if err != nil {
+			return nil, err
+		}
+		parentID, err := strconv.Atoi(fields[1])
+		if err != nil {
+			return nil, err
+		}
+		info := mountInfo{
+			id:           id,
+			parentID:     parentID,
+			majorMinor:   fields[2],
+			root:         fields[3],
+			mountPoint:   fields[4],
+			mountOptions: strings.Split(fields[5], ","),
+		}
+		// All fields until "-" are "optional fields".
+		i := 6
+		for ; i < len(fields) && fields[i] != "-"; i++ {
+			info.optionalFields = append(info.optionalFields, fields[i])
+		}
+		// Parse the rest 3 fields.
+		i++
+		if len(fields)-i < 3 {
+			return nil, fmt.Errorf("expect 3 fields in %s, got %d", line, len(fields)-i)
+		}
+		info.fsType = fields[i]
+		info.source = fields[i+1]
+		info.superOptions = strings.Split(fields[i+2], ",")
+		infos = append(infos, info)
+	}
+	return infos, nil
+}