mount_linux.go

package command

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strings"
)

const (
	/* 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) mount ID:  unique identifier of the mount (may be reused after umount)
	   (2) parent ID:  ID of parent (or of self for the top of the mount tree)
	   (3) major:minor:  value of st_dev for files on filesystem
	   (4) root:  root of the mount within the filesystem
	   (5) mount point:  mount point relative to the process's root
	   (6) mount options:  per mount options
	   (7) optional fields:  zero or more fields of the form "tag[:value]"
	   (8) separator:  marks the end of the optional fields
	   (9) filesystem type:  name of filesystem of the form "type[.subtype]"
	   (10) mount source:  filesystem specific information or "none"
	   (11) super options:  per super block options*/
	mountinfoFormat = "%d %d %d:%d %s %s %s %s"
)

// Info reveals information about a particular mounted filesystem. This
// struct is populated from the content in the /proc/<pid>/mountinfo file.
type Info struct {
	// ID is a unique identifier of the mount (may be reused after umount).
	ID int

	// Parent indicates the ID of the mount parent (or of self for the top of the
	// mount tree).
	Parent int

	// Major indicates one half of the device ID which identifies the device class.
	Major int

	// Minor indicates one half of the device ID which identifies a specific
	// instance of device.
	Minor int

	// Root of the mount within the filesystem.
	Root string

	// Mountpoint indicates the mount point relative to the process's root.
	Mountpoint string

	// Opts represents mount-specific options.
	Opts string

	// Optional represents optional fields.
	Optional string

	// Fstype indicates the type of filesystem, such as EXT3.
	Fstype string

	// Source indicates filesystem specific information or "none".
	Source string

	// VfsOpts represents per super block options.
	VfsOpts string
}

// Mounted determines if a specified mountpoint has been mounted.
// On Linux it looks at /proc/self/mountinfo and on Solaris at mnttab.
func mounted(mountPoint string) (bool, error) {
	entries, err := parseMountTable()
	if err != nil {
		return false, err
	}

	// Search the table for the mountPoint
	for _, e := range entries {
		if e.Mountpoint == mountPoint {
			return true, nil
		}
	}
	return false, nil
}

// Parse /proc/self/mountinfo because comparing Dev and ino does not work from
// bind mounts
func parseMountTable() ([]*Info, error) {
	f, err := os.Open("/proc/self/mountinfo")
	if err != nil {
		return nil, err
	}
	defer f.Close()

	return parseInfoFile(f)
}

func parseInfoFile(r io.Reader) ([]*Info, error) {
	var (
		s   = bufio.NewScanner(r)
		out []*Info
	)

	for s.Scan() {
		if err := s.Err(); err != nil {
			return nil, err
		}

		var (
			p              = &Info{}
			text           = s.Text()
			optionalFields string
		)

		if _, err := fmt.Sscanf(text, mountinfoFormat,
			&p.ID, &p.Parent, &p.Major, &p.Minor,
			&p.Root, &p.Mountpoint, &p.Opts, &optionalFields); err != nil {
			return nil, fmt.Errorf("Scanning '%s' failed: %s", text, err)
		}
		// Safe as mountinfo encodes mountpoints with spaces as \040.
		index := strings.Index(text, " - ")
		postSeparatorFields := strings.Fields(text[index+3:])
		if len(postSeparatorFields) < 3 {
			return nil, fmt.Errorf("Error found less than 3 fields post '-' in %q", text)
		}

		if optionalFields != "-" {
			p.Optional = optionalFields
		}

		p.Fstype = postSeparatorFields[0]
		p.Source = postSeparatorFields[1]
		p.VfsOpts = strings.Join(postSeparatorFields[2:], " ")
		out = append(out, p)
	}
	return out, nil
}

func checkMountPointAvailable(dir string) bool {
	mountPoint := dir
	if mountPoint != "/" && strings.HasSuffix(mountPoint, "/") {
		mountPoint = mountPoint[0 : len(mountPoint)-1]
	}

	if mounted, err := mounted(mountPoint); err != nil || mounted {
		return false
	}

	return true
}