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/fillqueue.go

@@ -0,0 +1,121 @@
+// 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 FillQueue is how a process tells the kernel which buffers are available
+// to be filled by incoming packets.
+//
+// FillQueue is not thread-safe and requires external synchronization
+type FillQueue 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 for incoming packets.
+	//
+	// 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 we update this value.
+	producer *atomicbitops.Uint32
+
+	// consumer points to the shared atomic value that indicates the last
+	// consumed descriptor. Only the kernel updates 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 used to atomically write *producer.
+	cachedProducer uint32
+	// cachedConsumer is updated when we atomically read *consumer.
+	// cachedConsumer is actually len(ring) larger than the real consumer
+	// value. See free() for details.
+	cachedConsumer uint32
+}
+
+// free returns the number of free descriptors in the fill queue.
+func (fq *FillQueue) free(toReserve uint32) uint32 {
+	// Try to find free descriptors without incurring an atomic operation.
+	//
+	// cachedConsumer is always len(fq.ring) larger than the real consumer
+	// value. This lets us, in the common case, compute the number of free
+	// descriptors simply via fq.cachedConsumer - fq.cachedProducer without
+	// also adding len(fq.ring).
+	if available := fq.cachedConsumer - fq.cachedProducer; available >= toReserve {
+		return available
+	}
+
+	// If we didn't already have enough descriptors available, check
+	// whether the kernel has returned some to us.
+	fq.cachedConsumer = fq.consumer.Load()
+	fq.cachedConsumer += uint32(len(fq.ring))
+	return fq.cachedConsumer - fq.cachedProducer
+}
+
+// Notify updates the producer such that it is visible to the kernel.
+func (fq *FillQueue) Notify() {
+	fq.producer.Store(fq.cachedProducer)
+}
+
+// Set sets the fill queue's descriptor at index to addr.
+func (fq *FillQueue) Set(index uint32, addr uint64) {
+	// Use mask to avoid overflowing and loop back around the ring.
+	fq.ring[index&fq.mask] = addr
+}
+
+// FillAll posts as many empty buffers as possible for the kernel to fill, then
+// notifies the kernel.
+//
+// +checklocks:umem.mu
+func (fq *FillQueue) FillAll(umem *UMEM) {
+	// Figure out how many buffers and queue slots are available.
+	available := fq.free(umem.nFreeFrames)
+	if available == 0 {
+		return
+	}
+	if available > umem.nFreeFrames {
+		available = umem.nFreeFrames
+	}
+
+	// Fill the queue as much as possible and notify the kernel.
+	index := fq.cachedProducer
+	fq.cachedProducer += available
+	for i := uint32(0); i < available; i++ {
+		fq.Set(index+i, umem.AllocFrame())
+	}
+	fq.Notify()
+}