github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/platform/interrupt/interrupt.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package interrupt provides an interrupt helper.
    16  package interrupt
    17  
    18  import (
    19  	"fmt"
    20  
    21  	"github.com/SagerNet/gvisor/pkg/sync"
    22  )
    23  
    24  // Receiver receives interrupt notifications from a Forwarder.
    25  type Receiver interface {
    26  	// NotifyInterrupt is called when the Receiver receives an interrupt.
    27  	NotifyInterrupt()
    28  }
    29  
    30  // Forwarder is a helper for delivering delayed signal interruptions.
    31  //
    32  // This helps platform implementations with Interrupt semantics.
    33  type Forwarder struct {
    34  	// mu protects the below.
    35  	mu sync.Mutex
    36  
    37  	// dst is the function to be called when NotifyInterrupt() is called. If
    38  	// dst is nil, pending will be set instead, causing the next call to
    39  	// Enable() to return false.
    40  	dst     Receiver
    41  	pending bool
    42  }
    43  
    44  // Enable attempts to enable interrupt forwarding to r. If f has already
    45  // received an interrupt, Enable does nothing and returns false. Otherwise,
    46  // future calls to f.NotifyInterrupt() cause r.NotifyInterrupt() to be called,
    47  // and Enable returns true.
    48  //
    49  // Usage:
    50  //
    51  // if !f.Enable(r) {
    52  //     // There was an interrupt.
    53  //     return
    54  // }
    55  // defer f.Disable()
    56  //
    57  // Preconditions:
    58  // * r must not be nil.
    59  // * f must not already be forwarding interrupts to a Receiver.
    60  func (f *Forwarder) Enable(r Receiver) bool {
    61  	if r == nil {
    62  		panic("nil Receiver")
    63  	}
    64  	f.mu.Lock()
    65  	if f.dst != nil {
    66  		f.mu.Unlock()
    67  		panic(fmt.Sprintf("already forwarding interrupts to %+v", f.dst))
    68  	}
    69  	if f.pending {
    70  		f.pending = false
    71  		f.mu.Unlock()
    72  		return false
    73  	}
    74  	f.dst = r
    75  	f.mu.Unlock()
    76  	return true
    77  }
    78  
    79  // Disable stops interrupt forwarding. If interrupt forwarding is already
    80  // disabled, Disable is a no-op.
    81  func (f *Forwarder) Disable() {
    82  	f.mu.Lock()
    83  	f.dst = nil
    84  	f.mu.Unlock()
    85  }
    86  
    87  // NotifyInterrupt implements Receiver.NotifyInterrupt. If interrupt forwarding
    88  // is enabled, the configured Receiver will be notified. Otherwise the
    89  // interrupt will be delivered to the next call to Enable.
    90  func (f *Forwarder) NotifyInterrupt() {
    91  	f.mu.Lock()
    92  	if f.dst != nil {
    93  		f.dst.NotifyInterrupt()
    94  	} else {
    95  		f.pending = true
    96  	}
    97  	f.mu.Unlock()
    98  }