github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/pkg/sentry/fsimpl/timerfd/timerfd.go (about)

     1  // Copyright 2020 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 timerfd implements timer fds.
    16  package timerfd
    17  
    18  import (
    19  	"github.com/MerlinKodo/gvisor/pkg/atomicbitops"
    20  	"github.com/MerlinKodo/gvisor/pkg/context"
    21  	"github.com/MerlinKodo/gvisor/pkg/errors/linuxerr"
    22  	"github.com/MerlinKodo/gvisor/pkg/hostarch"
    23  	ktime "github.com/MerlinKodo/gvisor/pkg/sentry/kernel/time"
    24  	"github.com/MerlinKodo/gvisor/pkg/sentry/vfs"
    25  	"github.com/MerlinKodo/gvisor/pkg/usermem"
    26  	"github.com/MerlinKodo/gvisor/pkg/waiter"
    27  )
    28  
    29  // TimerFileDescription implements vfs.FileDescriptionImpl for timer fds. It also
    30  // implements ktime.TimerListener.
    31  //
    32  // +stateify savable
    33  type TimerFileDescription struct {
    34  	vfsfd vfs.FileDescription
    35  	vfs.FileDescriptionDefaultImpl
    36  	vfs.DentryMetadataFileDescriptionImpl
    37  	vfs.NoLockFD
    38  
    39  	events waiter.Queue
    40  	timer  *ktime.Timer
    41  
    42  	// val is the number of timer expirations since the last successful
    43  	// call to PRead, or SetTime. val must be accessed using atomic memory
    44  	// operations.
    45  	val atomicbitops.Uint64
    46  }
    47  
    48  var _ vfs.FileDescriptionImpl = (*TimerFileDescription)(nil)
    49  var _ ktime.Listener = (*TimerFileDescription)(nil)
    50  
    51  // New returns a new timer fd.
    52  func New(ctx context.Context, vfsObj *vfs.VirtualFilesystem, clock ktime.Clock, flags uint32) (*vfs.FileDescription, error) {
    53  	vd := vfsObj.NewAnonVirtualDentry("[timerfd]")
    54  	defer vd.DecRef(ctx)
    55  	tfd := &TimerFileDescription{}
    56  	tfd.timer = ktime.NewTimer(clock, tfd)
    57  	if err := tfd.vfsfd.Init(tfd, flags, vd.Mount(), vd.Dentry(), &vfs.FileDescriptionOptions{
    58  		UseDentryMetadata: true,
    59  		DenyPRead:         true,
    60  		DenyPWrite:        true,
    61  	}); err != nil {
    62  		return nil, err
    63  	}
    64  	return &tfd.vfsfd, nil
    65  }
    66  
    67  // Read implements vfs.FileDescriptionImpl.Read.
    68  func (tfd *TimerFileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
    69  	const sizeofUint64 = 8
    70  	if dst.NumBytes() < sizeofUint64 {
    71  		return 0, linuxerr.EINVAL
    72  	}
    73  	if val := tfd.val.Swap(0); val != 0 {
    74  		var buf [sizeofUint64]byte
    75  		hostarch.ByteOrder.PutUint64(buf[:], val)
    76  		if _, err := dst.CopyOut(ctx, buf[:]); err != nil {
    77  			// Linux does not undo consuming the number of
    78  			// expirations even if writing to userspace fails.
    79  			return 0, err
    80  		}
    81  		return sizeofUint64, nil
    82  	}
    83  	return 0, linuxerr.ErrWouldBlock
    84  }
    85  
    86  // Clock returns the timer fd's Clock.
    87  func (tfd *TimerFileDescription) Clock() ktime.Clock {
    88  	return tfd.timer.Clock()
    89  }
    90  
    91  // GetTime returns the associated Timer's setting and the time at which it was
    92  // observed.
    93  func (tfd *TimerFileDescription) GetTime() (ktime.Time, ktime.Setting) {
    94  	return tfd.timer.Get()
    95  }
    96  
    97  // SetTime atomically changes the associated Timer's setting, resets the number
    98  // of expirations to 0, and returns the previous setting and the time at which
    99  // it was observed.
   100  func (tfd *TimerFileDescription) SetTime(s ktime.Setting) (ktime.Time, ktime.Setting) {
   101  	return tfd.timer.SwapAnd(s, func() { tfd.val.Store(0) })
   102  }
   103  
   104  // Readiness implements waiter.Waitable.Readiness.
   105  func (tfd *TimerFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
   106  	var ready waiter.EventMask
   107  	if tfd.val.Load() != 0 {
   108  		ready |= waiter.ReadableEvents
   109  	}
   110  	return ready
   111  }
   112  
   113  // EventRegister implements waiter.Waitable.EventRegister.
   114  func (tfd *TimerFileDescription) EventRegister(e *waiter.Entry) error {
   115  	tfd.events.EventRegister(e)
   116  	return nil
   117  }
   118  
   119  // EventUnregister implements waiter.Waitable.EventUnregister.
   120  func (tfd *TimerFileDescription) EventUnregister(e *waiter.Entry) {
   121  	tfd.events.EventUnregister(e)
   122  }
   123  
   124  // Epollable implements FileDescriptionImpl.Epollable.
   125  func (tfd *TimerFileDescription) Epollable() bool {
   126  	return true
   127  }
   128  
   129  // PauseTimer pauses the associated Timer.
   130  func (tfd *TimerFileDescription) PauseTimer() {
   131  	tfd.timer.Pause()
   132  }
   133  
   134  // ResumeTimer resumes the associated Timer.
   135  func (tfd *TimerFileDescription) ResumeTimer() {
   136  	tfd.timer.Resume()
   137  }
   138  
   139  // Release implements vfs.FileDescriptionImpl.Release.
   140  func (tfd *TimerFileDescription) Release(context.Context) {
   141  	tfd.timer.Destroy()
   142  }
   143  
   144  // NotifyTimer implements ktime.TimerListener.NotifyTimer.
   145  func (tfd *TimerFileDescription) NotifyTimer(exp uint64, setting ktime.Setting) (ktime.Setting, bool) {
   146  	tfd.val.Add(exp)
   147  	tfd.events.Notify(waiter.ReadableEvents)
   148  	return ktime.Setting{}, false
   149  }