From d02b74a5dcfed4bfc8f2f8e545bca4d2afabb296 Mon Sep 17 00:00:00 2001 From: Googler Date: Fri, 27 Apr 2018 10:37:02 -0700 Subject: Check in gVisor. PiperOrigin-RevId: 194583126 Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463 --- pkg/waiter/fdnotifier/fdnotifier.go | 200 ++++++++++++++++++++++++++++++++++++ 1 file changed, 200 insertions(+) create mode 100644 pkg/waiter/fdnotifier/fdnotifier.go (limited to 'pkg/waiter/fdnotifier/fdnotifier.go') diff --git a/pkg/waiter/fdnotifier/fdnotifier.go b/pkg/waiter/fdnotifier/fdnotifier.go new file mode 100644 index 000000000..8bb93e39b --- /dev/null +++ b/pkg/waiter/fdnotifier/fdnotifier.go @@ -0,0 +1,200 @@ +// Copyright 2018 Google Inc. +// +// 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. + +// Package fdnotifier contains an adapter that translates IO events (e.g., a +// file became readable/writable) from native FDs to the notifications in the +// waiter package. It uses epoll in edge-triggered mode to receive notifications +// for registered FDs. +package fdnotifier + +import ( + "fmt" + "sync" + "syscall" + + "gvisor.googlesource.com/gvisor/pkg/waiter" +) + +type fdInfo struct { + queue *waiter.Queue + waiting bool +} + +// notifier holds all the state necessary to issue notifications when IO events +// occur in the observed FDs. +type notifier struct { + // epFD is the epoll file descriptor used to register for io + // notifications. + epFD int + + // mu protects fdMap. + mu sync.Mutex + + // fdMap maps file descriptors to their notification queues and waiting + // status. + fdMap map[int32]*fdInfo +} + +// newNotifier creates a new notifier object. +func newNotifier() (*notifier, error) { + epfd, err := syscall.EpollCreate1(0) + if err != nil { + return nil, err + } + + w := ¬ifier{ + epFD: epfd, + fdMap: make(map[int32]*fdInfo), + } + + go w.waitAndNotify() // S/R-SAFE: no waiter exists during save / load. + + return w, nil +} + +// waitFD waits on mask for fd. The fdMap mutex must be hold. +func (n *notifier) waitFD(fd int32, fi *fdInfo, mask waiter.EventMask) error { + if !fi.waiting && mask == 0 { + return nil + } + + e := syscall.EpollEvent{ + Events: uint32(mask) | -syscall.EPOLLET, + Fd: fd, + } + + switch { + case !fi.waiting && mask != 0: + if err := syscall.EpollCtl(n.epFD, syscall.EPOLL_CTL_ADD, int(fd), &e); err != nil { + return err + } + fi.waiting = true + case fi.waiting && mask == 0: + syscall.EpollCtl(n.epFD, syscall.EPOLL_CTL_DEL, int(fd), nil) + fi.waiting = false + case fi.waiting && mask != 0: + if err := syscall.EpollCtl(n.epFD, syscall.EPOLL_CTL_MOD, int(fd), &e); err != nil { + return err + } + } + + return nil +} + +// addFD adds an FD to the list of FDs observed by n. +func (n *notifier) addFD(fd int32, queue *waiter.Queue) { + n.mu.Lock() + defer n.mu.Unlock() + + // Panic if we're already notifying on this FD. + if _, ok := n.fdMap[fd]; ok { + panic(fmt.Sprintf("File descriptor %v added twice", fd)) + } + + // We have nothing to wait for at the moment. Just add it to the map. + n.fdMap[fd] = &fdInfo{queue: queue} +} + +// updateFD updates the set of events the fd needs to be notified on. +func (n *notifier) updateFD(fd int32) error { + n.mu.Lock() + defer n.mu.Unlock() + + if fi, ok := n.fdMap[fd]; ok { + return n.waitFD(fd, fi, fi.queue.Events()) + } + + return nil +} + +// RemoveFD removes an FD from the list of FDs observed by n. +func (n *notifier) removeFD(fd int32) { + n.mu.Lock() + defer n.mu.Unlock() + + // Remove from map, then from epoll object. + n.waitFD(fd, n.fdMap[fd], 0) + delete(n.fdMap, fd) +} + +// hasFD returns true if the fd is in the list of observed FDs. +func (n *notifier) hasFD(fd int32) bool { + n.mu.Lock() + defer n.mu.Unlock() + + _, ok := n.fdMap[fd] + return ok +} + +// waitAndNotify run is its own goroutine and loops waiting for io event +// notifications from the epoll object. Once notifications arrive, they are +// dispatched to the registered queue. +func (n *notifier) waitAndNotify() error { + e := make([]syscall.EpollEvent, 100) + for { + v, err := epollWait(n.epFD, e, -1) + if err == syscall.EINTR { + continue + } + + if err != nil { + return err + } + + n.mu.Lock() + for i := 0; i < v; i++ { + if fi, ok := n.fdMap[e[i].Fd]; ok { + fi.queue.Notify(waiter.EventMask(e[i].Events)) + } + } + n.mu.Unlock() + } +} + +var shared struct { + notifier *notifier + once sync.Once + initErr error +} + +// AddFD adds an FD to the list of observed FDs. +func AddFD(fd int32, queue *waiter.Queue) error { + shared.once.Do(func() { + shared.notifier, shared.initErr = newNotifier() + }) + + if shared.initErr != nil { + return shared.initErr + } + + shared.notifier.addFD(fd, queue) + return nil +} + +// UpdateFD updates the set of events the fd needs to be notified on. +func UpdateFD(fd int32) error { + return shared.notifier.updateFD(fd) +} + +// RemoveFD removes an FD from the list of observed FDs. +func RemoveFD(fd int32) { + shared.notifier.removeFD(fd) +} + +// HasFD returns true if the FD is in the list of observed FDs. +// +// This should only be used by tests to assert that FDs are correctly registered. +func HasFD(fd int32) bool { + return shared.notifier.hasFD(fd) +} -- cgit v1.2.3