From 4d1276ba85ccb1b386bfa6373915f351ccc1fdc1 Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Thu, 5 Dec 2013 22:22:55 +0100
Subject: [PATCH] devicemapper: Unmount inactive devices

This implements the new Put() operation such that
Get()/Put() maintains a refcount for each ID, mounting
only on first Get() and unmounting on the last Get().

This means we avoid littering the system with lots of mounts
and active devicemapper devices and free resources related
to them.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

asdfljk
Upstream-commit: 886f650d9b2133fb61e7cc5b0bb7795246852026
Component: engine
---
 .../engine/graphdriver/devmapper/driver.go    | 41 +++++++++++++++++--
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/components/engine/graphdriver/devmapper/driver.go b/components/engine/graphdriver/devmapper/driver.go
index 0bf5fb24e1..dae712b9b5 100644
--- a/components/engine/graphdriver/devmapper/driver.go
+++ b/components/engine/graphdriver/devmapper/driver.go
@@ -5,8 +5,10 @@ package devmapper
 import (
 	"fmt"
 	"github.com/dotcloud/docker/graphdriver"
+	"github.com/dotcloud/docker/utils"
 	"io/ioutil"
 	"path"
+	"sync"
 )
 
 func init() {
@@ -20,7 +22,9 @@ func init() {
 
 type Driver struct {
 	*DeviceSet
-	home string
+	home       string
+	sync.Mutex // Protects concurrent modification to active
+	active     map[string]int
 }
 
 var Init = func(home string) (graphdriver.Driver, error) {
@@ -31,6 +35,7 @@ var Init = func(home string) (graphdriver.Driver, error) {
 	d := &Driver{
 		DeviceSet: deviceSet,
 		home:      home,
+		active:    make(map[string]int),
 	}
 	return d, nil
 }
@@ -82,6 +87,14 @@ func (d *Driver) Create(id, parent string) error {
 }
 
 func (d *Driver) Remove(id string) error {
+	// Protect the d.active from concurrent access
+	d.Lock()
+	defer d.Unlock()
+
+	if d.active[id] != 0 {
+		utils.Errorf("Warning: removing active id %s\n", id)
+	}
+
 	mp := path.Join(d.home, "mnt", id)
 	if err := d.unmount(id, mp); err != nil {
 		return err
@@ -90,14 +103,36 @@ func (d *Driver) Remove(id string) error {
 }
 
 func (d *Driver) Get(id string) (string, error) {
+	// Protect the d.active from concurrent access
+	d.Lock()
+	defer d.Unlock()
+
+	count := d.active[id]
+
 	mp := path.Join(d.home, "mnt", id)
-	if err := d.mount(id, mp); err != nil {
-		return "", err
+	if count == 0 {
+		if err := d.mount(id, mp); err != nil {
+			return "", err
+		}
 	}
+
+	d.active[id] = count + 1
+
 	return path.Join(mp, "rootfs"), nil
 }
 
 func (d *Driver) Put(id string) {
+	// Protect the d.active from concurrent access
+	d.Lock()
+	defer d.Unlock()
+
+	if count := d.active[id]; count > 1 {
+		d.active[id] = count - 1
+	} else {
+		mp := path.Join(d.home, "mnt", id)
+		d.unmount(id, mp)
+		delete(d.active, id)
+	}
 }
 
 func (d *Driver) mount(id, mountPoint string) error {