snapshot: sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1

Содержимое пина, зафиксированного в go.mod sing-box-lx, одним коммитом
без истории. Полная история SagerNet/gvisor — 1.45 ГБ и клонируется в
каждой CI-джобе; наша дельта — одна вставка в одну функцию, история для
неё не нужна.

Module path github.com/sagernet/gvisor сохранён намеренно: на него
опирается replace-директива суперпроекта.

Патч поверх — отдельным коммитом, чтобы дельта читалась одним git show
и переносилась на новый пин копированием.

SPECS/TASKS/048-GVISOR_HANDSHAKE_NIL_CRASH

pkg/xdp/completionqueue.go

@@ -0,0 +1,119 @@
+// Copyright 2022 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.
+
+//go:build amd64 || arm64
+// +build amd64 arm64
+
+package xdp
+
+import (
+	"github.com/sagernet/gvisor/pkg/atomicbitops"
+)
+
+// The CompletionQueue is how the kernel tells a process which buffers have
+// been transmitted and can be reused.
+//
+// CompletionQueue is not thread-safe and requires external synchronization
+type CompletionQueue struct {
+	// mem is the mmap'd area shared with the kernel. Many other fields of
+	// this struct point into mem.
+	mem []byte
+
+	// ring is the actual ring buffer. It is a list of frame addresses
+	// ready to be reused.
+	//
+	// len(ring) must be a power of 2.
+	ring []uint64
+
+	// mask is used whenever indexing into ring. It is always len(ring)-1.
+	// It prevents index out of bounds errors while allowing the producer
+	// and consumer pointers to repeatedly "overflow" and loop back around
+	// the ring.
+	mask uint32
+
+	// producer points to the shared atomic value that indicates the last
+	// produced descriptor. Only the kernel updates this value.
+	producer *atomicbitops.Uint32
+
+	// consumer points to the shared atomic value that indicates the last
+	// consumed descriptor. Only we update this value.
+	consumer *atomicbitops.Uint32
+
+	// flags points to the shared atomic value that holds flags for the
+	// queue.
+	flags *atomicbitops.Uint32
+
+	// Cached values are used to avoid relatively expensive atomic
+	// operations. They are used, incremented, and decremented multiple
+	// times with non-atomic operations, and then "batch-updated" by
+	// reading or writing atomically to synchronize with the kernel.
+
+	// cachedProducer is updated when we atomically read *producer.
+	cachedProducer uint32
+	// cachedConsumer is used to atomically write *consumer.
+	cachedConsumer uint32
+}
+
+// Peek returns the number of buffers available to reuse as well as the index
+// at which they start. Peek will only return a buffer once, so callers must
+// process any received buffers.
+func (cq *CompletionQueue) Peek() (nAvailable, index uint32) {
+	// Get the number of available buffers and update cachedConsumer to
+	// reflect that we're going to consume them.
+	entries := cq.free()
+	index = cq.cachedConsumer
+	cq.cachedConsumer += entries
+	return entries, index
+}
+
+func (cq *CompletionQueue) free() uint32 {
+	// Return any buffers we know about without incurring an atomic
+	// operation if possible.
+	entries := cq.cachedProducer - cq.cachedConsumer
+	// If we're not aware of any completed packets, refresh the producer
+	// pointer to see whether the kernel enqueued anything.
+	if entries == 0 {
+		cq.cachedProducer = cq.producer.Load()
+		entries = cq.cachedProducer - cq.cachedConsumer
+	}
+	return entries
+}
+
+// Release notifies the kernel that we have consumed nDone packets.
+func (cq *CompletionQueue) Release(nDone uint32) {
+	// We don't have to use an atomic add because only we update this; the
+	// kernel just reads it.
+	cq.consumer.Store(cq.consumer.RacyLoad() + nDone)
+}
+
+// Get gets the descriptor at index.
+func (cq *CompletionQueue) Get(index uint32) uint64 {
+	// Use mask to avoid overflowing and loop back around the ring.
+	return cq.ring[index&cq.mask]
+}
+
+// FreeAll dequeues as many buffers as possible from the queue and returns them
+// to the UMEM.
+//
+// +checklocks:umem.mu
+func (cq *CompletionQueue) FreeAll(umem *UMEM) {
+	available, index := cq.Peek()
+	if available < 1 {
+		return
+	}
+	for i := uint32(0); i < available; i++ {
+		umem.FreeFrame(cq.Get(index + i))
+	}
+	cq.Release(available)
+}