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// Copyright 2018 Google LLC
//
// 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 port provides port ID allocation for netlink sockets.
//
// A netlink port is any int32 value. Positive ports are typically equivalent
// to the PID of the binding process. If that port is unavailable, negative
// ports are searched to find a free port that will not conflict with other
// PIDS.
package port
import (
"fmt"
"math"
"math/rand"
"sync"
)
// maxPorts is a sanity limit on the maximum number of ports to allocate per
// protocol.
const maxPorts = 10000
// Manager allocates netlink port IDs.
//
// +stateify savable
type Manager struct {
// mu protects the fields below.
mu sync.Mutex `state:"nosave"`
// ports contains a map of allocated ports for each protocol.
ports map[int]map[int32]struct{}
}
// New creates a new Manager.
func New() *Manager {
return &Manager{
ports: make(map[int]map[int32]struct{}),
}
}
// Allocate reserves a new port ID for protocol. hint will be taken if
// available.
func (m *Manager) Allocate(protocol int, hint int32) (int32, bool) {
m.mu.Lock()
defer m.mu.Unlock()
proto, ok := m.ports[protocol]
if !ok {
proto = make(map[int32]struct{})
// Port 0 is reserved for the kernel.
proto[0] = struct{}{}
m.ports[protocol] = proto
}
if len(proto) >= maxPorts {
return 0, false
}
if _, ok := proto[hint]; !ok {
// Hint is available, reserve it.
proto[hint] = struct{}{}
return hint, true
}
// Search for any free port in [math.MinInt32, -4096). The positive
// port space is left open for pid-based allocations. This behavior is
// consistent with Linux.
start := int32(math.MinInt32 + rand.Int63n(math.MaxInt32-4096+1))
curr := start
for {
if _, ok := proto[curr]; !ok {
proto[curr] = struct{}{}
return curr, true
}
curr--
if curr >= -4096 {
curr = -4097
}
if curr == start {
// Nothing found. We should always find a free port
// because maxPorts < -4096 - MinInt32.
panic(fmt.Sprintf("No free port found in %+v", proto))
}
}
}
// Release frees the specified port for protocol.
//
// Preconditions: port is already allocated.
func (m *Manager) Release(protocol int, port int32) {
m.mu.Lock()
defer m.mu.Unlock()
proto, ok := m.ports[protocol]
if !ok {
panic(fmt.Sprintf("Released port %d for protocol %d which has no allocations", port, protocol))
}
if _, ok := proto[port]; !ok {
panic(fmt.Sprintf("Released port %d for protocol %d is not allocated", port, protocol))
}
delete(proto, port)
}
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