sandbox/vfs: implement proc_pid_mountinfo(5) parser

Test cases are mostly taken from util-linux. This implementation is more correct and slightly faster than the one found in github:kubernetes/utils.

Signed-off-by: Ophestra <cat@gensokyo.uk>

sandbox/vfs/mountinfo.go

@@ -0,0 +1,141 @@
+package vfs
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+var (
+	ErrMountInfoFields = errors.New("unexpected field count")
+	ErrMountInfoEmpty  = errors.New("unexpected empty field")
+	ErrMountInfoDevno  = errors.New("bad maj:min field")
+	ErrMountInfoSep    = errors.New("bad optional fields separator")
+)
+
+type (
+	// MountInfo represents a /proc/pid/mountinfo document.
+	MountInfo struct {
+		Next *MountInfo
+		MountInfoEntry
+	}
+
+	// MountInfoEntry represents a line in /proc/pid/mountinfo.
+	MountInfoEntry struct {
+		// mount ID: a unique ID for the mount (may be reused after umount(2)).
+		ID int `json:"id"`
+		// parent ID: the ID of the parent mount (or of self for the root of this mount namespace's mount tree).
+		Parent int `json:"parent"`
+		// major:minor: the value of st_dev for files on this filesystem (see stat(2)).
+		Devno DevT `json:"devno"`
+		// root: the pathname of the directory in the filesystem which forms the root of this mount.
+		Root string `json:"root"`
+		// mount point: the pathname of the mount point relative to the process's root directory.
+		Target string `json:"target"`
+		// mount options: per-mount options (see mount(2)).
+		VfsOptstr string `json:"vfs_optstr"`
+		// optional fields: zero or more fields of the form "tag[:value]"; see below.
+		// separator: the end of the optional fields is marked by a single hyphen.
+		OptFields []string `json:"opt_fields"`
+		// filesystem type: the filesystem type in the form "type[.subtype]".
+		FsType string `json:"fstype"`
+		// mount source: filesystem-specific information or "none".
+		Source string `json:"source"`
+		// super options: per-superblock options (see mount(2)).
+		FsOptstr string `json:"fs_optstr"`
+	}
+
+	DevT [2]int
+)
+
+// ParseMountInfo parses a mountinfo file according to proc_pid_mountinfo(5).
+func ParseMountInfo(r io.Reader) (*MountInfo, error) {
+	var m, cur *MountInfo
+	s := bufio.NewScanner(r)
+	for s.Scan() {
+		if cur == nil {
+			m = new(MountInfo)
+			cur = m
+		} else {
+			cur.Next = new(MountInfo)
+			cur = cur.Next
+		}
+
+		// prevent proceeding with misaligned fields due to optional fields
+		f := strings.Split(s.Text(), " ")
+		if len(f) < 10 {
+			return nil, ErrMountInfoFields
+		}
+
+		// 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
+		// (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
+
+		// (1) id
+		if id, err := strconv.Atoi(f[0]); err != nil { // 0
+			return nil, err
+		} else {
+			cur.ID = id
+		}
+
+		// (2) parent
+		if parent, err := strconv.Atoi(f[1]); err != nil { // 1
+			return nil, err
+		} else {
+			cur.Parent = parent
+		}
+
+		// (3) maj:min
+		if n, err := fmt.Sscanf(f[2], "%d:%d", &cur.Devno[0], &cur.Devno[1]); err != nil {
+			return nil, err
+		} else if n != 2 {
+			// unreachable
+			return nil, ErrMountInfoDevno
+		}
+
+		// (4) mountroot
+		cur.Root = Unmangle(f[3])
+		if cur.Root == "" {
+			return nil, ErrMountInfoEmpty
+		}
+
+		// (5) target
+		cur.Target = Unmangle(f[4])
+		if cur.Target == "" {
+			return nil, ErrMountInfoEmpty
+		}
+
+		// (6) vfs options (fs-independent)
+		cur.VfsOptstr = Unmangle(f[5])
+		if cur.VfsOptstr == "" {
+			return nil, ErrMountInfoEmpty
+		}
+
+		// (7) optional fields, terminated by " - "
+		i := len(f) - 4
+		cur.OptFields = f[6:i]
+
+		// (8) optional fields end marker
+		if f[i] != "-" {
+			return nil, ErrMountInfoSep
+		}
+		i++
+
+		// (9) FS type
+		cur.FsType = Unmangle(f[i])
+		if cur.FsType == "" {
+			return nil, ErrMountInfoEmpty
+		}
+		i++
+
+		// (10) source -- maybe empty string
+		cur.Source = Unmangle(f[i])
+		i++
+
+		// (11) fs options (fs specific)
+		cur.FsOptstr = Unmangle(f[i])
+	}
+	return m, s.Err()
+}