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devmapper: Keep track of used device Ids in a bitmap

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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>
This commit is contained in:
Vivek Goyal 2014-12-03 13:06:43 -05:00 committed by root
parent 359a38b26a
commit 4d39e056aa
1 changed files with 30 additions and 2 deletions
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32
daemon/graphdriver/devmapper/deviceset.go
View file

@ -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