1 files changed, 48 insertions, 18 deletions
diff --git a/pkg/sentry/vfs/dentry.go b/pkg/sentry/vfs/dentry.go
index 24af13eb1..320ab7ce1 100644
--- a/pkg/sentry/vfs/dentry.go
+++ b/pkg/sentry/vfs/dentry.go
@@ -17,6 +17,7 @@ package vfs
 import (
 	"sync/atomic"
 
+	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -88,6 +89,8 @@ func (d *Dentry) Impl() DentryImpl {
 // DentryImpl contains implementation details for a Dentry. Implementations of
 // DentryImpl should contain their associated Dentry by value as their first
 // field.
+//
+// +stateify savable
 type DentryImpl interface {
 	// IncRef increments the Dentry's reference count. A Dentry with a non-zero
 	// reference count must remain coherent with the state of the filesystem.
@@ -102,7 +105,7 @@ type DentryImpl interface {
 	TryIncRef() bool
 
 	// DecRef decrements the Dentry's reference count.
-	DecRef()
+	DecRef(ctx context.Context)
 
 	// InotifyWithParent notifies all watches on the targets represented by this
 	// dentry and its parent. The parent's watches are notified first, followed
@@ -113,12 +116,29 @@ type DentryImpl interface {
 	//
 	// Note that the events may not actually propagate up to the user, depending
 	// on the event masks.
-	InotifyWithParent(events uint32, cookie uint32, et EventType)
+	InotifyWithParent(ctx context.Context, events, cookie uint32, et EventType)
 
 	// Watches returns the set of inotify watches for the file corresponding to
 	// the Dentry. Dentries that are hard links to the same underlying file
 	// share the same watches.
+	//
+	// Watches may return nil if the dentry belongs to a FilesystemImpl that
+	// does not support inotify. If an implementation returns a non-nil watch
+	// set, it must always return a non-nil watch set. Likewise, if an
+	// implementation returns a nil watch set, it must always return a nil watch
+	// set.
+	//
+	// The caller does not need to hold a reference on the dentry.
 	Watches() *Watches
+
+	// OnZeroWatches is called whenever the number of watches on a dentry drops
+	// to zero. This is needed by some FilesystemImpls (e.g. gofer) to manage
+	// dentry lifetime.
+	//
+	// The caller does not need to hold a reference on the dentry. OnZeroWatches
+	// may acquire inotify locks, so to prevent deadlock, no inotify locks should
+	// be held by the caller.
+	OnZeroWatches(ctx context.Context)
 }
 
 // IncRef increments d's reference count.
@@ -133,8 +153,8 @@ func (d *Dentry) TryIncRef() bool {
 }
 
 // DecRef decrements d's reference count.
-func (d *Dentry) DecRef() {
-	d.impl.DecRef()
+func (d *Dentry) DecRef(ctx context.Context) {
+	d.impl.DecRef(ctx)
 }
 
 // IsDead returns true if d has been deleted or invalidated by its owning
@@ -149,17 +169,26 @@ func (d *Dentry) isMounted() bool {
 	return atomic.LoadUint32(&d.mounts) != 0
 }
 
-// InotifyWithParent notifies all watches on the inodes for this dentry and
+// InotifyWithParent notifies all watches on the targets represented by d and
 // its parent of events.
-func (d *Dentry) InotifyWithParent(events uint32, cookie uint32, et EventType) {
-	d.impl.InotifyWithParent(events, cookie, et)
+func (d *Dentry) InotifyWithParent(ctx context.Context, events, cookie uint32, et EventType) {
+	d.impl.InotifyWithParent(ctx, events, cookie, et)
 }
 
 // Watches returns the set of inotify watches associated with d.
+//
+// Watches will return nil if d belongs to a FilesystemImpl that does not
+// support inotify.
 func (d *Dentry) Watches() *Watches {
 	return d.impl.Watches()
 }
 
+// OnZeroWatches performs cleanup tasks whenever the number of watches on a
+// dentry drops to zero.
+func (d *Dentry) OnZeroWatches(ctx context.Context) {
+	d.impl.OnZeroWatches(ctx)
+}
+
 // The following functions are exported so that filesystem implementations can
 // use them. The vfs package, and users of VFS, should not call these
 // functions.
@@ -188,11 +217,11 @@ func (vfs *VirtualFilesystem) AbortDeleteDentry(d *Dentry) {
 
 // CommitDeleteDentry must be called after PrepareDeleteDentry if the deletion
 // succeeds.
-func (vfs *VirtualFilesystem) CommitDeleteDentry(d *Dentry) {
+func (vfs *VirtualFilesystem) CommitDeleteDentry(ctx context.Context, d *Dentry) {
 	d.dead = true
 	d.mu.Unlock()
 	if d.isMounted() {
-		vfs.forgetDeadMountpoint(d)
+		vfs.forgetDeadMountpoint(ctx, d)
 	}
 }
 
@@ -200,12 +229,12 @@ func (vfs *VirtualFilesystem) CommitDeleteDentry(d *Dentry) {
 // did for reasons outside of VFS' control (e.g. d represents the local state
 // of a file on a remote filesystem on which the file has already been
 // deleted).
-func (vfs *VirtualFilesystem) InvalidateDentry(d *Dentry) {
+func (vfs *VirtualFilesystem) InvalidateDentry(ctx context.Context, d *Dentry) {
 	d.mu.Lock()
 	d.dead = true
 	d.mu.Unlock()
 	if d.isMounted() {
-		vfs.forgetDeadMountpoint(d)
+		vfs.forgetDeadMountpoint(ctx, d)
 	}
 }
 
@@ -215,8 +244,9 @@ func (vfs *VirtualFilesystem) InvalidateDentry(d *Dentry) {
 // caller must call AbortRenameDentry, CommitRenameReplaceDentry, or
 // CommitRenameExchangeDentry depending on the rename's outcome.
 //
-// Preconditions: If to is not nil, it must be a child Dentry from the same
-// Filesystem. from != to.
+// Preconditions:
+// * If to is not nil, it must be a child Dentry from the same Filesystem.
+// * from != to.
 func (vfs *VirtualFilesystem) PrepareRenameDentry(mntns *MountNamespace, from, to *Dentry) error {
 	vfs.mountMu.Lock()
 	if mntns.mountpoints[from] != 0 {
@@ -252,13 +282,13 @@ func (vfs *VirtualFilesystem) AbortRenameDentry(from, to *Dentry) {
 // that was replaced by from.
 //
 // Preconditions: PrepareRenameDentry was previously called on from and to.
-func (vfs *VirtualFilesystem) CommitRenameReplaceDentry(from, to *Dentry) {
+func (vfs *VirtualFilesystem) CommitRenameReplaceDentry(ctx context.Context, from, to *Dentry) {
 	from.mu.Unlock()
 	if to != nil {
 		to.dead = true
 		to.mu.Unlock()
 		if to.isMounted() {
-			vfs.forgetDeadMountpoint(to)
+			vfs.forgetDeadMountpoint(ctx, to)
 		}
 	}
 }
@@ -277,7 +307,7 @@ func (vfs *VirtualFilesystem) CommitRenameExchangeDentry(from, to *Dentry) {
 //
 // forgetDeadMountpoint is analogous to Linux's
 // fs/namespace.c:__detach_mounts().
-func (vfs *VirtualFilesystem) forgetDeadMountpoint(d *Dentry) {
+func (vfs *VirtualFilesystem) forgetDeadMountpoint(ctx context.Context, d *Dentry) {
 	var (
 		vdsToDecRef    []VirtualDentry
 		mountsToDecRef []*Mount
@@ -290,9 +320,9 @@ func (vfs *VirtualFilesystem) forgetDeadMountpoint(d *Dentry) {
 	vfs.mounts.seq.EndWrite()
 	vfs.mountMu.Unlock()
 	for _, vd := range vdsToDecRef {
-		vd.DecRef()
+		vd.DecRef(ctx)
 	}
 	for _, mnt := range mountsToDecRef {
-		mnt.DecRef()
+		mnt.DecRef(ctx)
 	}
 }