283 lines
7.2 KiB
Go
283 lines
7.2 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 eventfd provides an implementation of Linux's file-based event
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// notification.
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package eventfd
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import (
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"math"
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"sync"
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"syscall"
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"gvisor.googlesource.com/gvisor/pkg/abi/linux"
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"gvisor.googlesource.com/gvisor/pkg/fdnotifier"
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"gvisor.googlesource.com/gvisor/pkg/sentry/context"
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"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
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"gvisor.googlesource.com/gvisor/pkg/sentry/fs/anon"
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"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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"gvisor.googlesource.com/gvisor/pkg/syserror"
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"gvisor.googlesource.com/gvisor/pkg/waiter"
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)
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// EventOperations represents an event with the semantics of Linux's file-based event
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// notification (eventfd). Eventfds are usually internal to the Sentry but in certain
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// situations they may be converted into a host-backed eventfd.
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//
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// +stateify savable
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type EventOperations struct {
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fsutil.FileNoopRelease `state:"nosave"`
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fsutil.FilePipeSeek `state:"nosave"`
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fsutil.FileNotDirReaddir `state:"nosave"`
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fsutil.FileNoFsync `state:"nosave"`
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fsutil.FileNoopFlush `state:"nosave"`
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fsutil.FileNoMMap `state:"nosave"`
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fsutil.FileNoIoctl `state:"nosave"`
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fsutil.FileUseInodeUnstableAttr `state:"nosave"`
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// Mutex that protects accesses to the fields of this event.
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mu sync.Mutex `state:"nosave"`
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// Queue is used to notify interested parties when the event object
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// becomes readable or writable.
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wq waiter.Queue `state:"zerovalue"`
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// val is the current value of the event counter.
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val uint64
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// semMode specifies whether the event is in "semaphore" mode.
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semMode bool
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// hostfd indicates whether this eventfd is passed through to the host.
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hostfd int
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}
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// New creates a new event object with the supplied initial value and mode.
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func New(ctx context.Context, initVal uint64, semMode bool) *fs.File {
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// name matches fs/eventfd.c:eventfd_file_create.
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dirent := fs.NewDirent(anon.NewInode(ctx), "anon_inode:[eventfd]")
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return fs.NewFile(ctx, dirent, fs.FileFlags{Read: true, Write: true}, &EventOperations{
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val: initVal,
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semMode: semMode,
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hostfd: -1,
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})
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}
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// HostFD returns the host eventfd associated with this event.
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func (e *EventOperations) HostFD() (int, error) {
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e.mu.Lock()
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defer e.mu.Unlock()
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if e.hostfd >= 0 {
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return e.hostfd, nil
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}
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flags := linux.EFD_NONBLOCK
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if e.semMode {
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flags |= linux.EFD_SEMAPHORE
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}
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fd, _, err := syscall.Syscall(syscall.SYS_EVENTFD2, uintptr(e.val), uintptr(flags), 0)
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if err != 0 {
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return -1, err
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}
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if err := fdnotifier.AddFD(int32(fd), &e.wq); err != nil {
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syscall.Close(int(fd))
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return -1, err
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}
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e.hostfd = int(fd)
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return e.hostfd, nil
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}
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// Release implements fs.FileOperations.Release.
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func (e *EventOperations) Release() {
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e.mu.Lock()
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defer e.mu.Unlock()
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if e.hostfd >= 0 {
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fdnotifier.RemoveFD(int32(e.hostfd))
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syscall.Close(e.hostfd)
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e.hostfd = -1
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}
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}
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// Read implements fs.FileOperations.Read.
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func (e *EventOperations) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, _ int64) (int64, error) {
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if dst.NumBytes() < 8 {
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return 0, syscall.EINVAL
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}
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if err := e.read(ctx, dst); err != nil {
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return 0, err
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}
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return 8, nil
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}
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// Write implements fs.FileOperations.Write.
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func (e *EventOperations) Write(ctx context.Context, _ *fs.File, src usermem.IOSequence, _ int64) (int64, error) {
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if src.NumBytes() < 8 {
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return 0, syscall.EINVAL
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}
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if err := e.write(ctx, src); err != nil {
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return 0, err
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}
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return 8, nil
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}
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// Must be called with e.mu locked.
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func (e *EventOperations) hostRead(ctx context.Context, dst usermem.IOSequence) error {
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var buf [8]byte
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if _, err := syscall.Read(e.hostfd, buf[:]); err != nil {
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if err == syscall.EWOULDBLOCK {
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return syserror.ErrWouldBlock
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}
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return err
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}
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_, err := dst.CopyOut(ctx, buf[:])
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return err
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}
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func (e *EventOperations) read(ctx context.Context, dst usermem.IOSequence) error {
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e.mu.Lock()
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if e.hostfd >= 0 {
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defer e.mu.Unlock()
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return e.hostRead(ctx, dst)
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}
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// We can't complete the read if the value is currently zero.
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if e.val == 0 {
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e.mu.Unlock()
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return syserror.ErrWouldBlock
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}
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// Update the value based on the mode the event is operating in.
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var val uint64
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if e.semMode {
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val = 1
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// Consistent with Linux, this is done even if writing to memory fails.
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e.val--
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} else {
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val = e.val
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e.val = 0
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}
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e.mu.Unlock()
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// Notify writers. We do this even if we were already writable because
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// it is possible that a writer is waiting to write the maximum value
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// to the event.
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e.wq.Notify(waiter.EventOut)
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var buf [8]byte
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usermem.ByteOrder.PutUint64(buf[:], val)
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_, err := dst.CopyOut(ctx, buf[:])
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return err
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}
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// Must be called with e.mu locked.
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func (e *EventOperations) hostWrite(val uint64) error {
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var buf [8]byte
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usermem.ByteOrder.PutUint64(buf[:], val)
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_, err := syscall.Write(e.hostfd, buf[:])
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if err == syscall.EWOULDBLOCK {
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return syserror.ErrWouldBlock
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}
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return err
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}
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func (e *EventOperations) write(ctx context.Context, src usermem.IOSequence) error {
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var buf [8]byte
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if _, err := src.CopyIn(ctx, buf[:]); err != nil {
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return err
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}
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val := usermem.ByteOrder.Uint64(buf[:])
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return e.Signal(val)
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}
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// Signal is an internal function to signal the event fd.
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func (e *EventOperations) Signal(val uint64) error {
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if val == math.MaxUint64 {
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return syscall.EINVAL
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}
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e.mu.Lock()
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if e.hostfd >= 0 {
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defer e.mu.Unlock()
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return e.hostWrite(val)
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}
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// We only allow writes that won't cause the value to go over the max
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// uint64 minus 1.
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if val > math.MaxUint64-1-e.val {
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e.mu.Unlock()
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return syserror.ErrWouldBlock
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}
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e.val += val
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e.mu.Unlock()
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// Always trigger a notification.
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e.wq.Notify(waiter.EventIn)
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return nil
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}
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// Readiness returns the ready events for the event fd.
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func (e *EventOperations) Readiness(mask waiter.EventMask) waiter.EventMask {
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e.mu.Lock()
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if e.hostfd >= 0 {
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defer e.mu.Unlock()
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return fdnotifier.NonBlockingPoll(int32(e.hostfd), mask)
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}
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ready := waiter.EventMask(0)
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if e.val > 0 {
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ready |= waiter.EventIn
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}
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if e.val < math.MaxUint64-1 {
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ready |= waiter.EventOut
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}
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e.mu.Unlock()
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return mask & ready
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}
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// EventRegister implements waiter.Waitable.EventRegister.
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func (e *EventOperations) EventRegister(entry *waiter.Entry, mask waiter.EventMask) {
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e.wq.EventRegister(entry, mask)
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e.mu.Lock()
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defer e.mu.Unlock()
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if e.hostfd >= 0 {
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fdnotifier.UpdateFD(int32(e.hostfd))
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}
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}
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// EventUnregister implements waiter.Waitable.EventUnregister.
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func (e *EventOperations) EventUnregister(entry *waiter.Entry) {
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e.wq.EventUnregister(entry)
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e.mu.Lock()
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defer e.mu.Unlock()
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if e.hostfd >= 0 {
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fdnotifier.UpdateFD(int32(e.hostfd))
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}
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}
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