Serializing bitseq alloc

Previously the bitseq alloc was allocating the first available bit from the
begining of the sequence. With this commit the bitseq alloc will proceed
from the current allocation. This change will affect the way ipam and vni
allocation is done currently. The ip allocation will be done sequentially
from the previous allocation as opposed to the first available IP.

Signed-off-by: Abhinandan Prativadi <abhi@docker.com>

libnetwork/bitseq/sequence.go

@@ -41,6 +41,7 @@ type Handle struct {
 	id         string
 	dbIndex    uint64
 	dbExists   bool
+	curr       uint64
 	store      datastore.DataStore
 	sync.Mutex
 }
@@ -193,6 +194,7 @@ func (h *Handle) getCopy() *Handle {
 		dbIndex:    h.dbIndex,
 		dbExists:   h.dbExists,
 		store:      h.store,
+		curr:       h.curr,
 	}
 }
 
@@ -323,10 +325,10 @@ func (h *Handle) set(ordinal, start, end uint64, any bool, release bool) (uint64
 			bytePos, bitPos = ordinalToPos(ordinal)
 		} else {
 			if any {
-				bytePos, bitPos, err = getFirstAvailable(h.head, start)
+				bytePos, bitPos, err = getAvailableFromCurrent(h.head, start, h.curr, end)
 				ret = posToOrdinal(bytePos, bitPos)
-				if end < ret {
-					err = ErrNoBitAvailable
+				if err == nil {
+					h.curr = ret + 1
 				}
 			} else {
 				bytePos, bitPos, err = checkIfAvailable(h.head, ordinal)
@@ -515,6 +517,29 @@ func getFirstAvailable(head *sequence, start uint64) (uint64, uint64, error) {
 	return invalidPos, invalidPos, ErrNoBitAvailable
 }
 
+//getAvailableFromCurrent will look for available ordinal from the current ordinal.
+// If none found then it will loop back to the start to check of the available bit.
+//This can be further optimized to check from start till curr in case of a rollover
+func getAvailableFromCurrent(head *sequence, start, curr, end uint64) (uint64, uint64, error) {
+	var bytePos, bitPos uint64
+	if curr != 0 && curr > start {
+		bytePos, bitPos, _ = getFirstAvailable(head, curr)
+		ret := posToOrdinal(bytePos, bitPos)
+		if end < ret {
+			goto begin
+		}
+		return bytePos, bitPos, nil
+	}
+
+begin:
+	bytePos, bitPos, _ = getFirstAvailable(head, start)
+	ret := posToOrdinal(bytePos, bitPos)
+	if end < ret {
+		return invalidPos, invalidPos, ErrNoBitAvailable
+	}
+	return bytePos, bitPos, nil
+}
+
 // checkIfAvailable checks if the bit correspondent to the specified ordinal is unset
 // If the ordinal is beyond the sequence limits, a negative response is returned
 func checkIfAvailable(head *sequence, ordinal uint64) (uint64, uint64, error) {

libnetwork/bitseq/store.go

@@ -87,6 +87,7 @@ func (h *Handle) CopyTo(o datastore.KVObject) error {
 	dstH.dbIndex = h.dbIndex
 	dstH.dbExists = h.dbExists
 	dstH.store = h.store
+	dstH.curr = h.curr
 	dstH.Unlock()
 
 	return nil

libnetwork/libnetwork_internal_test.go

@@ -614,7 +614,7 @@ func TestIpamReleaseOnNetDriverFailures(t *testing.T) {
 	}
 	defer ep.Delete(false)
 
-	expectedIP, _ := types.ParseCIDR("10.34.0.1/16")
+	expectedIP, _ := types.ParseCIDR("10.34.0.2/16")
 	if !types.CompareIPNet(ep.Info().Iface().Address(), expectedIP) {
 		t.Fatalf("Ipam release must have failed, endpoint has unexpected address: %v", ep.Info().Iface().Address())
 	}