Faster mountinfo parser

libcontainer/factory_linux_test.go

@@ -108,26 +108,21 @@ func TestFactoryNewTmpfs(t *testing.T) {
 	if !mounted {
 		t.Fatalf("Factory Root is not mounted")
 	}
-	mounts, err := mount.GetMounts()
+	mounts, err := mount.GetMounts(mount.SingleEntryFilter(lfactory.Root))
 	if err != nil {
 		t.Fatal(err)
 	}
-	var found bool
-	for _, m := range mounts {
-		if m.Mountpoint == lfactory.Root {
-			if m.Fstype != "tmpfs" {
-				t.Fatalf("Fstype of root: %s, expected %s", m.Fstype, "tmpfs")
-			}
-			if m.Source != "tmpfs" {
-				t.Fatalf("Source of root: %s, expected %s", m.Source, "tmpfs")
-			}
-			found = true
-		}
-	}
-	if !found {
+	if len(mounts) != 1 {
 		t.Fatalf("Factory Root is not listed in mounts list")
 	}
-	defer unix.Unmount(root, unix.MNT_DETACH)
+	m := mounts[0]
+	if m.Fstype != "tmpfs" {
+		t.Fatalf("Fstype of root: %s, expected %s", m.Fstype, "tmpfs")
+	}
+	if m.Source != "tmpfs" {
+		t.Fatalf("Source of root: %s, expected %s", m.Source, "tmpfs")
+	}
+	unix.Unmount(root, unix.MNT_DETACH)
 }
 
 func TestFactoryLoadNotExists(t *testing.T) {

libcontainer/mount/mount.go

@@ -1,23 +1,18 @@
 package mount
 
-// GetMounts retrieves a list of mounts for the current running process.
-func GetMounts() ([]*Info, error) {
-	return parseMountTable()
+// GetMounts retrieves a list of mounts for the current running process,
+// with an optional filter applied (use nil for no filter).
+func GetMounts(f FilterFunc) ([]*Info, error) {
+	return parseMountTable(f)
 }
 
-// Mounted looks at /proc/self/mountinfo to determine of the specified
-// mountpoint has been mounted
+// Mounted determines if a specified mountpoint has been mounted.
+// On Linux it looks at /proc/self/mountinfo.
 func Mounted(mountpoint string) (bool, error) {
-	entries, err := parseMountTable()
+	entries, err := GetMounts(SingleEntryFilter(mountpoint))
 	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
+	return len(entries) > 0, nil
 }

libcontainer/mount/mountinfo_filters.go

@@ -0,0 +1,56 @@
+package mount
+
+import "strings"
+
+// FilterFunc is a type defining a callback function for GetMount(),
+// used to filter out mountinfo entries we're not interested in.
+//
+// It takes a pointer to the Info struct (not fully populated,
+// currently only Mountpoint is filled in), and returns two booleans:
+//
+//  - skip: true if the entry should be skipped
+//  - stop: true if parsing should be stopped after the entry
+type FilterFunc func(*Info) (skip, stop bool)
+
+// PrefixFilter discards all entries whose mount points
+// do not start with a specific prefix
+func PrefixFilter(prefix string) FilterFunc {
+	return func(m *Info) (bool, bool) {
+		skip := !strings.HasPrefix(m.Mountpoint, prefix)
+		return skip, false
+	}
+}
+
+// SingleEntryFilter looks for a specific entry
+func SingleEntryFilter(mp string) FilterFunc {
+	return func(m *Info) (bool, bool) {
+		if m.Mountpoint == mp {
+			return false, true // don't skip, stop now
+		}
+		return true, false // skip, keep going
+	}
+}
+
+// ParentsFilter returns all entries whose mount points
+// can be parents of a path specified, discarding others.
+//
+// For example, given `/var/lib/docker/something`, entries
+// like `/var/lib/docker`, `/var` and `/` are returned.
+func ParentsFilter(path string) FilterFunc {
+	return func(m *Info) (bool, bool) {
+		skip := !strings.HasPrefix(path, m.Mountpoint)
+		return skip, false
+	}
+}
+
+// FstypeFilter returns all entries that match provided fstype(s).
+func FstypeFilter(fstype ...string) FilterFunc {
+	return func(m *Info) (bool, bool) {
+		for _, t := range fstype {
+			if m.Fstype == t {
+				return false, false // don't skeep, keep going
+			}
+		}
+		return true, false // skip, keep going
+	}
+}

libcontainer/mount/mountinfo_linux.go

@@ -0,0 +1,139 @@
+package mount
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func parseInfoFile(r io.Reader, filter FilterFunc) ([]*Info, error) {
+	s := bufio.NewScanner(r)
+	out := []*Info{}
+	var err error
+	for s.Scan() {
+		if err = s.Err(); err != nil {
+			return nil, err
+		}
+		/*
+		   See http://man7.org/linux/man-pages/man5/proc.5.html
+
+		   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
+
+		   In other words, we have:
+		    * 6 mandatory fields	(1)..(6)
+		    * 0 or more optional fields	(7)
+		    * a separator field		(8)
+		    * 3 mandatory fields	(9)..(11)
+		*/
+
+		text := s.Text()
+		fields := strings.Split(text, " ")
+		numFields := len(fields)
+		if numFields < 10 {
+			// should be at least 10 fields
+			return nil, fmt.Errorf("Parsing '%s' failed: not enough fields (%d)", text, numFields)
+		}
+
+		// separator field
+		sepIdx := numFields - 4
+		// In Linux <= 3.9 mounting a cifs with spaces in a share
+		// name (like "//srv/My Docs") _may_ end up having a space
+		// in the last field of mountinfo (like "unc=//serv/My Docs").
+		// Since kernel 3.10-rc1, cifs option "unc=" is ignored,
+		// so spaces should not appear.
+		//
+		// Check for a separator, and work around the spaces bug
+		for fields[sepIdx] != "-" {
+			sepIdx--
+			if sepIdx == 5 {
+				return nil, fmt.Errorf("Parsing '%s' failed: missing - separator", text)
+			}
+		}
+
+		p := &Info{}
+
+		// Fill in the fields that a filter might check
+		// (currently only Mountpoint and Fstype)
+		p.Mountpoint, err = strconv.Unquote(`"` + fields[4] + `"`)
+		if err != nil {
+			return nil, fmt.Errorf("Parsing '%s' failed: unable to unquote mount point field: %v", fields[4], err)
+		}
+		p.Fstype = fields[sepIdx+1]
+
+		// Run a filter soon so we can skip parsing/adding entries
+		// the caller is not interested in
+		var skip, stop bool
+		if filter != nil {
+			skip, stop = filter(p)
+			if skip {
+				continue
+			}
+		}
+
+		// Fill in the rest of the fields
+
+		// ignore any numbers parsing errors, as there should not be any
+		p.ID, _ = strconv.Atoi(fields[0])
+		p.Parent, _ = strconv.Atoi(fields[1])
+		mm := strings.Split(fields[2], ":")
+		if len(mm) != 2 {
+			return nil, fmt.Errorf("Parsing '%s' failed: unexpected minor:major pair %s", text, mm)
+		}
+		p.Major, _ = strconv.Atoi(mm[0])
+		p.Minor, _ = strconv.Atoi(mm[1])
+
+		p.Root, err = strconv.Unquote(`"` + fields[3] + `"`)
+		if err != nil {
+			return nil, fmt.Errorf("Parsing '%s' failed: unable to unquote root field: %v", fields[3], err)
+		}
+
+		p.Opts = fields[5]
+
+		// zero or more optional fields
+		switch {
+		case sepIdx == 6:
+			// zero, do nothing
+		case sepIdx == 7:
+			p.Optional = fields[6]
+		default:
+			p.Optional = strings.Join(fields[6:sepIdx-1], " ")
+		}
+
+		p.Source = fields[sepIdx+2]
+		p.VfsOpts = fields[sepIdx+3]
+
+		out = append(out, p)
+		if stop {
+			break
+		}
+	}
+	return out, nil
+}
+
+// Parse /proc/self/mountinfo because comparing Dev and ino does not work from
+// bind mounts
+func parseMountTable(filter FilterFunc) ([]*Info, error) {
+	f, err := os.Open("/proc/self/mountinfo")
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	return parseInfoFile(f, filter)
+}