Remove waiter.Entry.Context

This field is redundant since state can be stored in the callback.

PiperOrigin-RevId: 318134855

pkg/sentry/kernel/epoll/epoll.go

@@ -271,11 +271,13 @@ func (e *EventPoll) ReadEvents(max int) []linux.EpollEvent {
 
 // readyCallback is called when one of the files we're polling becomes ready. It
 // moves said file to the readyList if it's currently in the waiting list.
-type readyCallback struct{}
+type readyCallback struct {
+	context *pollEntry
+}
 
 // Callback implements waiter.EntryCallback.Callback.
-func (*readyCallback) Callback(w *waiter.Entry) {
-	entry := w.Context.(*pollEntry)
+func (r *readyCallback) Callback(*waiter.Entry) {
+	entry := r.context
 	e := entry.epoll
 
 	e.listsMu.Lock()
@@ -310,7 +312,7 @@ func (e *EventPoll) initEntryReadiness(entry *pollEntry) {
 	// Check if the file happens to already be in a ready state.
 	ready := f.Readiness(entry.mask) & entry.mask
 	if ready != 0 {
-		(*readyCallback).Callback(nil, &entry.waiter)
+		(&readyCallback{context: entry}).Callback(&entry.waiter)
 	}
 }
 
@@ -380,10 +382,9 @@ func (e *EventPoll) AddEntry(id FileIdentifier, flags EntryFlags, mask waiter.Ev
 		userData: data,
 		epoll:    e,
 		flags:    flags,
-		waiter:   waiter.Entry{Callback: &readyCallback{}},
 		mask:     mask,
 	}
-	entry.waiter.Context = entry
+	entry.waiter.Callback = &readyCallback{context: entry}
 	e.files[id] = entry
 	entry.file = refs.NewWeakRef(id.File, entry)
 

pkg/sentry/kernel/epoll/epoll_state.go

@@ -21,8 +21,7 @@ import (
 
 // afterLoad is invoked by stateify.
 func (p *pollEntry) afterLoad() {
-	p.waiter = waiter.Entry{Callback: &readyCallback{}}
-	p.waiter.Context = p
+	p.waiter.Callback = &readyCallback{context: p}
 	p.file = refs.NewWeakRef(p.id.File, p)
 	p.id.File.EventRegister(&p.waiter, p.mask)
 }

pkg/waiter/waiter.go

@@ -128,13 +128,6 @@ type EntryCallback interface {
 //
 // +stateify savable
 type Entry struct {
-	// Context stores any state the waiter may wish to store in the entry
-	// itself, which may be used at wake up time.
-	//
-	// Note that use of this field is optional and state may alternatively be
-	// stored in the callback itself.
-	Context interface{}
-
 	Callback EntryCallback
 
 	// The following fields are protected by the queue lock.
@@ -142,13 +135,14 @@ type Entry struct {
 	waiterEntry
 }
 
-type channelCallback struct{}
+type channelCallback struct {
+	ch chan struct{}
+}
 
 // Callback implements EntryCallback.Callback.
-func (*channelCallback) Callback(e *Entry) {
-	ch := e.Context.(chan struct{})
+func (c *channelCallback) Callback(*Entry) {
 	select {
-	case ch <- struct{}{}:
+	case c.ch <- struct{}{}:
 	default:
 	}
 }
@@ -164,7 +158,7 @@ func NewChannelEntry(c chan struct{}) (Entry, chan struct{}) {
 		c = make(chan struct{}, 1)
 	}
 
-	return Entry{Context: c, Callback: &channelCallback{}}, c
+	return Entry{Callback: &channelCallback{ch: c}}, c
 }
 
 // Queue represents the wait queue where waiters can be added and