From 622c433bcbb5ab83d049da74061fa717d16a92fd Mon Sep 17 00:00:00 2001
From: Vivek Goyal <vgoyal@redhat.com>
Date: Wed, 3 Dec 2014 13:06:43 -0500
Subject: [PATCH] devmapper: Keep track of used device Ids in a bitmap

Currently devicemapper backend does not keep track of used device Ids in
the pool. It tries a device Id and if that device Id exists in pool, it
tries with a different Id and keeps on doing this in a loop till it succeeds.

This worked fine so far but now we are moving to transaction based
device creation and deletion. We will keep deviceId information in
transaction which will be rolled back if docker crashed before transaction
was complete.

If we store a deviceId in transaction and later figure out it already
existed in pool and docker crashed, then we will rollback and remove
that existing device Id from pool (which we should not have).

That means, we should know free device Id in pool in advance before
we put that device Id in transaction.

Hence this patch creates a bitmap (one bit each for a deviceId), and
sets the bit if device Id is used otherwise resets it. This patch
is just preparing the ground right now. Actual usage will follow
in later patches.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Upstream-commit: 4d39e056aac2fadffcb8560101f3c31a2b7db3ae
Component: engine
---
 .../daemon/graphdriver/devmapper/deviceset.go | 32 +++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/components/engine/daemon/graphdriver/devmapper/deviceset.go b/components/engine/daemon/graphdriver/devmapper/deviceset.go
index 802d2e6562..d721861282 100644
--- a/components/engine/daemon/graphdriver/devmapper/deviceset.go
+++ b/components/engine/daemon/graphdriver/devmapper/deviceset.go
@@ -30,7 +30,9 @@ var (
 	DefaultDataLoopbackSize     int64  = 100 * 1024 * 1024 * 1024
 	DefaultMetaDataLoopbackSize int64  = 2 * 1024 * 1024 * 1024
 	DefaultBaseFsSize           uint64 = 10 * 1024 * 1024 * 1024
-	DefaultThinpBlockSize       uint32 = 128 // 64K = 128 512b sectors
+	DefaultThinpBlockSize       uint32 = 128      // 64K = 128 512b sectors
+	MaxDeviceId                 int    = 0xffffff // 24 bit, pool limit
+	DeviceIdMapSz               int    = (MaxDeviceId + 1) / 8
 )
 
 const deviceSetMetaFile string = "deviceset-metadata"
@@ -75,6 +77,7 @@ type DeviceSet struct {
 	devicePrefix  string
 	TransactionId uint64 `json:"-"`
 	NextDeviceId  int    `json:"next_device_id"`
+	deviceIdMap   []byte
 
 	// Options
 	dataLoopbackSize     int64
@@ -261,6 +264,30 @@ func (devices *DeviceSet) saveMetadata(info *DevInfo) error {
 	return nil
 }
 
+func (devices *DeviceSet) markDeviceIdUsed(deviceId int) {
+	var mask byte
+	i := deviceId % 8
+	mask = 1 << uint(i)
+	devices.deviceIdMap[deviceId/8] = devices.deviceIdMap[deviceId/8] | mask
+}
+
+func (devices *DeviceSet) markDeviceIdFree(deviceId int) {
+	var mask byte
+	i := deviceId % 8
+	mask = ^(1 << uint(i))
+	devices.deviceIdMap[deviceId/8] = devices.deviceIdMap[deviceId/8] & mask
+}
+
+func (devices *DeviceSet) isDeviceIdFree(deviceId int) bool {
+	var mask byte
+	i := deviceId % 8
+	mask = (1 << uint(i))
+	if (devices.deviceIdMap[deviceId/8] & mask) != 0 {
+		return false
+	}
+	return true
+}
+
 func (devices *DeviceSet) lookupDevice(hash string) (*DevInfo, error) {
 	devices.devicesLock.Lock()
 	defer devices.devicesLock.Unlock()
@@ -407,7 +434,7 @@ func (devices *DeviceSet) initMetaData() error {
 
 func (devices *DeviceSet) incNextDeviceId() {
 	// Ids are 24bit, so wrap around
-	devices.NextDeviceId = (devices.NextDeviceId + 1) & 0xffffff
+	devices.NextDeviceId = (devices.NextDeviceId + 1) & MaxDeviceId
 }
 
 func (devices *DeviceSet) createDevice(deviceId *int) error {
@@ -1333,6 +1360,7 @@ func NewDeviceSet(root string, doInit bool, options []string) (*DeviceSet, error
 		filesystem:           "ext4",
 		doBlkDiscard:         true,
 		thinpBlockSize:       DefaultThinpBlockSize,
+		deviceIdMap:          make([]byte, DeviceIdMapSz),
 	}
 
 	foundBlkDiscard := false