117 lines
3.0 KiB
Go
117 lines
3.0 KiB
Go
// Copyright 2018 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package port provides port ID allocation for netlink sockets.
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//
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// A netlink port is any int32 value. Positive ports are typically equivalent
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// to the PID of the binding process. If that port is unavailable, negative
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// ports are searched to find a free port that will not conflict with other
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// PIDS.
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package port
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import (
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"fmt"
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"math"
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"math/rand"
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"sync"
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)
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// maxPorts is a sanity limit on the maximum number of ports to allocate per
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// protocol.
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const maxPorts = 10000
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// Manager allocates netlink port IDs.
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//
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// +stateify savable
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type Manager struct {
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// mu protects the fields below.
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mu sync.Mutex `state:"nosave"`
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// ports contains a map of allocated ports for each protocol.
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ports map[int]map[int32]struct{}
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}
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// New creates a new Manager.
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func New() *Manager {
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return &Manager{
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ports: make(map[int]map[int32]struct{}),
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}
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}
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// Allocate reserves a new port ID for protocol. hint will be taken if
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// available.
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func (m *Manager) Allocate(protocol int, hint int32) (int32, bool) {
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m.mu.Lock()
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defer m.mu.Unlock()
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proto, ok := m.ports[protocol]
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if !ok {
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proto = make(map[int32]struct{})
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// Port 0 is reserved for the kernel.
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proto[0] = struct{}{}
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m.ports[protocol] = proto
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}
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if len(proto) >= maxPorts {
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return 0, false
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}
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if _, ok := proto[hint]; !ok {
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// Hint is available, reserve it.
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proto[hint] = struct{}{}
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return hint, true
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}
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// Search for any free port in [math.MinInt32, -4096). The positive
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// port space is left open for pid-based allocations. This behavior is
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// consistent with Linux.
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start := int32(math.MinInt32 + rand.Int63n(math.MaxInt32-4096+1))
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curr := start
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for {
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if _, ok := proto[curr]; !ok {
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proto[curr] = struct{}{}
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return curr, true
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}
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curr--
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if curr >= -4096 {
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curr = -4097
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}
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if curr == start {
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// Nothing found. We should always find a free port
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// because maxPorts < -4096 - MinInt32.
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panic(fmt.Sprintf("No free port found in %+v", proto))
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}
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}
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}
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// Release frees the specified port for protocol.
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//
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// Preconditions: port is already allocated.
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func (m *Manager) Release(protocol int, port int32) {
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m.mu.Lock()
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defer m.mu.Unlock()
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proto, ok := m.ports[protocol]
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if !ok {
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panic(fmt.Sprintf("Released port %d for protocol %d which has no allocations", port, protocol))
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}
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if _, ok := proto[port]; !ok {
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panic(fmt.Sprintf("Released port %d for protocol %d is not allocated", port, protocol))
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}
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delete(proto, port)
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}
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