Avoid an allocation in epoll

PiperOrigin-RevId: 318346153

pkg/sentry/kernel/epoll/epoll.go

@@ -107,7 +107,7 @@ type EventPoll struct {
 	// different lock to avoid circular lock acquisition order involving
 	// the wait queue mutexes and mu. The full order is mu, observed file
 	// wait queue mutex, then listsMu; this allows listsMu to be acquired
-	// when readyCallback is called.
+	// when (*pollEntry).Callback is called.
 	//
 	// An entry is always in one of the following lists:
 	//	readyList -- when there's a chance that it's ready to have
@@ -116,7 +116,7 @@ type EventPoll struct {
 	//		readEvents() functions always call the entry's file
 	//		Readiness() function to confirm it's ready.
 	//	waitingList -- when there's no chance that the entry is ready,
-	//		so it's waiting for the readyCallback to be called
+	//		so it's waiting for the (*pollEntry).Callback to be called
 	//		on it before it gets moved to the readyList.
 	//	disabledList -- when the entry is disabled. This happens when
 	//		a one-shot entry gets delivered via readEvents().
@@ -269,23 +269,19 @@ func (e *EventPoll) ReadEvents(max int) []linux.EpollEvent {
 	return ret
 }
 
-// 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 {
-	context *pollEntry
-}
-
 // Callback implements waiter.EntryCallback.Callback.
-func (r *readyCallback) Callback(*waiter.Entry) {
-	entry := r.context
-	e := entry.epoll
+//
+// Callback 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.
+func (p *pollEntry) Callback(*waiter.Entry) {
+	e := p.epoll
 
 	e.listsMu.Lock()
 
-	if entry.curList == &e.waitingList {
-		e.waitingList.Remove(entry)
-		e.readyList.PushBack(entry)
-		entry.curList = &e.readyList
+	if p.curList == &e.waitingList {
+		e.waitingList.Remove(p)
+		e.readyList.PushBack(p)
+		p.curList = &e.readyList
 		e.listsMu.Unlock()
 
 		e.Notify(waiter.EventIn)
@@ -312,7 +308,7 @@ 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{context: entry}).Callback(&entry.waiter)
+		entry.Callback(&entry.waiter)
 	}
 }
 
@@ -384,7 +380,7 @@ func (e *EventPoll) AddEntry(id FileIdentifier, flags EntryFlags, mask waiter.Ev
 		flags:    flags,
 		mask:     mask,
 	}
-	entry.waiter.Callback = &readyCallback{context: entry}
+	entry.waiter.Callback = entry
 	e.files[id] = entry
 	entry.file = refs.NewWeakRef(id.File, entry)
 
@@ -407,7 +403,7 @@ func (e *EventPoll) UpdateEntry(id FileIdentifier, flags EntryFlags, mask waiter
 	}
 
 	// Unregister the old mask and remove entry from the list it's in, so
-	// readyCallback is guaranteed to not be called on this entry anymore.
+	// (*pollEntry).Callback is guaranteed to not be called on this entry anymore.
 	entry.id.File.EventUnregister(&entry.waiter)
 
 	// Remove entry from whatever list it's in. This ensure that no other

pkg/sentry/kernel/epoll/epoll_state.go

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