1 files changed, 260 insertions, 0 deletions
diff --git a/vfs/mountinfo.go b/vfs/mountinfo.go
new file mode 100644
index 00000000..bcb3063f
--- /dev/null
+++ b/vfs/mountinfo.go
@@ -0,0 +1,260 @@
+// Package vfs provides bindings and iterators over proc_pid_mountinfo(5).
+package vfs
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"iter"
+	"slices"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+const (
+	MS_NOSYMFOLLOW = 0x100
+)
+
+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 (
+	// A MountInfoDecoder reads and decodes proc_pid_mountinfo(5) entries from an input stream.
+	MountInfoDecoder struct {
+		s *bufio.Scanner
+		m *MountInfo
+
+		current  *MountInfo
+		parseErr error
+		complete bool
+	}
+
+	// MountInfo represents the contents of a proc_pid_mountinfo(5) document.
+	MountInfo struct {
+		Next *MountInfo
+		MountInfoEntry
+	}
+
+	// MountInfoEntry represents a proc_pid_mountinfo(5) entry.
+	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
+)
+
+// Flags interprets VfsOptstr and returns the resulting flags and unmatched options.
+func (e *MountInfoEntry) Flags() (flags uintptr, unmatched []string) {
+	for _, s := range strings.Split(e.VfsOptstr, ",") {
+		switch s {
+		case "rw":
+		case "ro":
+			flags |= syscall.MS_RDONLY
+		case "nosuid":
+			flags |= syscall.MS_NOSUID
+		case "nodev":
+			flags |= syscall.MS_NODEV
+		case "noexec":
+			flags |= syscall.MS_NOEXEC
+		case "nosymfollow":
+			flags |= MS_NOSYMFOLLOW
+		case "noatime":
+			flags |= syscall.MS_NOATIME
+		case "nodiratime":
+			flags |= syscall.MS_NODIRATIME
+		case "relatime":
+			flags |= syscall.MS_RELATIME
+		default:
+			unmatched = append(unmatched, s)
+		}
+	}
+	return
+}
+
+// NewMountInfoDecoder returns a new decoder that reads from r.
+//
+// The decoder introduces its own buffering and may read data from r beyond the mountinfo entries requested.
+func NewMountInfoDecoder(r io.Reader) *MountInfoDecoder {
+	return &MountInfoDecoder{s: bufio.NewScanner(r)}
+}
+
+func (d *MountInfoDecoder) Decode(v **MountInfo) (err error) {
+	for d.scan() {
+	}
+	err = d.Err()
+	if err == nil {
+		*v = d.m
+	}
+	return
+}
+
+// Entries returns an iterator over mountinfo entries.
+func (d *MountInfoDecoder) Entries() iter.Seq[*MountInfoEntry] {
+	return func(yield func(*MountInfoEntry) bool) {
+		for cur := d.m; cur != nil; cur = cur.Next {
+			if !yield(&cur.MountInfoEntry) {
+				return
+			}
+		}
+		for d.scan() {
+			if !yield(&d.current.MountInfoEntry) {
+				return
+			}
+		}
+	}
+}
+
+func (d *MountInfoDecoder) Err() error {
+	if err := d.s.Err(); err != nil {
+		return err
+	}
+	return d.parseErr
+}
+
+func (d *MountInfoDecoder) scan() bool {
+	if d.complete {
+		return false
+	}
+	if !d.s.Scan() {
+		d.complete = true
+		return false
+	}
+
+	m := new(MountInfo)
+	if err := parseMountInfoLine(d.s.Text(), &m.MountInfoEntry); err != nil {
+		d.parseErr = err
+		d.complete = true
+		return false
+	}
+
+	if d.current == nil {
+		d.m = m
+		d.current = d.m
+	} else {
+		d.current.Next = m
+		d.current = d.current.Next
+	}
+	return true
+}
+
+func parseMountInfoLine(s string, ent *MountInfoEntry) error {
+	// prevent proceeding with misaligned fields due to optional fields
+	f := strings.Split(s, " ")
+	if len(f) < 10 {
+		return 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 err
+	} else {
+		ent.ID = id
+	}
+
+	// (2) parent
+	if parent, err := strconv.Atoi(f[1]); err != nil { // 1
+		return err
+	} else {
+		ent.Parent = parent
+	}
+
+	// (3) maj:min
+	if n, err := fmt.Sscanf(f[2], "%d:%d", &ent.Devno[0], &ent.Devno[1]); err != nil {
+		return err
+	} else if n != 2 {
+		// unreachable
+		return ErrMountInfoDevno
+	}
+
+	// (4) mountroot
+	ent.Root = Unmangle(f[3])
+	if ent.Root == "" {
+		return ErrMountInfoEmpty
+	}
+
+	// (5) target
+	ent.Target = Unmangle(f[4])
+	if ent.Target == "" {
+		return ErrMountInfoEmpty
+	}
+
+	// (6) vfs options (fs-independent)
+	ent.VfsOptstr = Unmangle(f[5])
+	if ent.VfsOptstr == "" {
+		return ErrMountInfoEmpty
+	}
+
+	// (7) optional fields, terminated by " - "
+	i := len(f) - 4
+	ent.OptFields = f[6:i]
+
+	// (8) optional fields end marker
+	if f[i] != "-" {
+		return ErrMountInfoSep
+	}
+	i++
+
+	// (9) FS type
+	ent.FsType = Unmangle(f[i])
+	if ent.FsType == "" {
+		return ErrMountInfoEmpty
+	}
+	i++
+
+	// (10) source -- maybe empty string
+	ent.Source = Unmangle(f[i])
+	i++
+
+	// (11) fs options (fs specific)
+	ent.FsOptstr = Unmangle(f[i])
+
+	return nil
+}
+
+func (e *MountInfoEntry) EqualWithIgnore(want *MountInfoEntry, ignore string) bool {
+	return (e.ID == want.ID || want.ID == -1) &&
+		(e.Parent == want.Parent || want.Parent == -1) &&
+		(e.Devno == want.Devno || (want.Devno[0] == -1 && want.Devno[1] == -1)) &&
+		(e.Root == want.Root || want.Root == ignore) &&
+		(e.Target == want.Target || want.Target == ignore) &&
+		(e.VfsOptstr == want.VfsOptstr || want.VfsOptstr == ignore) &&
+		(slices.Equal(e.OptFields, want.OptFields) || (len(want.OptFields) == 1 && want.OptFields[0] == ignore)) &&
+		(e.FsType == want.FsType || want.FsType == ignore) &&
+		(e.Source == want.Source || want.Source == ignore) &&
+		(e.FsOptstr == want.FsOptstr || want.FsOptstr == ignore)
+}
+
+func (e *MountInfoEntry) String() string {
+	return fmt.Sprintf("%d %d %d:%d %s %s %s %s %s %s %s",
+		e.ID, e.Parent, e.Devno[0], e.Devno[1], e.Root, e.Target, e.VfsOptstr,
+		strings.Join(append(e.OptFields, "-"), " "), e.FsType, e.Source, e.FsOptstr)
+}