1 files changed, 150 insertions, 0 deletions
diff --git a/pkg/tcpip/ports/flags.go b/pkg/tcpip/ports/flags.go
new file mode 100644
index 000000000..a8d7bff25
--- /dev/null
+++ b/pkg/tcpip/ports/flags.go
@@ -0,0 +1,150 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ports
+
+// Flags represents the type of port reservation.
+//
+// +stateify savable
+type Flags struct {
+	// MostRecent represents UDP SO_REUSEADDR.
+	MostRecent bool
+
+	// LoadBalanced indicates SO_REUSEPORT.
+	//
+	// LoadBalanced takes precidence over MostRecent.
+	LoadBalanced bool
+
+	// TupleOnly represents TCP SO_REUSEADDR.
+	TupleOnly bool
+}
+
+// Bits converts the Flags to their bitset form.
+func (f Flags) Bits() BitFlags {
+	var rf BitFlags
+	if f.MostRecent {
+		rf |= MostRecentFlag
+	}
+	if f.LoadBalanced {
+		rf |= LoadBalancedFlag
+	}
+	if f.TupleOnly {
+		rf |= TupleOnlyFlag
+	}
+	return rf
+}
+
+// Effective returns the effective behavior of a flag config.
+func (f Flags) Effective() Flags {
+	e := f
+	if e.LoadBalanced && e.MostRecent {
+		e.MostRecent = false
+	}
+	return e
+}
+
+// BitFlags is a bitset representation of Flags.
+type BitFlags uint32
+
+const (
+	// MostRecentFlag represents Flags.MostRecent.
+	MostRecentFlag BitFlags = 1 << iota
+
+	// LoadBalancedFlag represents Flags.LoadBalanced.
+	LoadBalancedFlag
+
+	// TupleOnlyFlag represents Flags.TupleOnly.
+	TupleOnlyFlag
+
+	// nextFlag is the value that the next added flag will have.
+	//
+	// It is used to calculate FlagMask below. It is also the number of
+	// valid flag states.
+	nextFlag
+
+	// FlagMask is a bit mask for BitFlags.
+	FlagMask = nextFlag - 1
+
+	// MultiBindFlagMask contains the flags that allow binding the same
+	// tuple multiple times.
+	MultiBindFlagMask = MostRecentFlag | LoadBalancedFlag
+)
+
+// ToFlags converts the bitset into a Flags struct.
+func (f BitFlags) ToFlags() Flags {
+	return Flags{
+		MostRecent:   f&MostRecentFlag != 0,
+		LoadBalanced: f&LoadBalancedFlag != 0,
+		TupleOnly:    f&TupleOnlyFlag != 0,
+	}
+}
+
+// FlagCounter counts how many references each flag combination has.
+type FlagCounter struct {
+	// refs stores the count for each possible flag combination, (0 though
+	// FlagMask).
+	refs [nextFlag]int
+}
+
+// AddRef increases the reference count for a specific flag combination.
+func (c *FlagCounter) AddRef(flags BitFlags) {
+	c.refs[flags]++
+}
+
+// DropRef decreases the reference count for a specific flag combination.
+func (c *FlagCounter) DropRef(flags BitFlags) {
+	c.refs[flags]--
+}
+
+// TotalRefs calculates the total number of references for all flag
+// combinations.
+func (c FlagCounter) TotalRefs() int {
+	var total int
+	for _, r := range c.refs {
+		total += r
+	}
+	return total
+}
+
+// FlagRefs returns the number of references with all specified flags.
+func (c FlagCounter) FlagRefs(flags BitFlags) int {
+	var total int
+	for i, r := range c.refs {
+		if BitFlags(i)&flags == flags {
+			total += r
+		}
+	}
+	return total
+}
+
+// AllRefsHave returns if all references have all specified flags.
+func (c FlagCounter) AllRefsHave(flags BitFlags) bool {
+	for i, r := range c.refs {
+		if BitFlags(i)&flags != flags && r > 0 {
+			return false
+		}
+	}
+	return true
+}
+
+// SharedFlags returns the set of flags shared by all references.
+func (c FlagCounter) SharedFlags() BitFlags {
+	intersection := FlagMask
+	for i, r := range c.refs {
+		if r > 0 {
+			intersection &= BitFlags(i)
+		}
+	}
+	return intersection
+}