Port inotify to vfs2, with support in tmpfs.

Support in other filesystem impls is still needed. Unlike in Linux and vfs1, we
need to plumb inotify down to each filesystem implementation in order to keep
track of links/inode structures properly.

IN_EXCL_UNLINK still needs to be implemented, as well as a few inotify hooks
that are not present in either vfs1 or vfs2. Those will be addressed in
subsequent changes.

Updates #1479.

PiperOrigin-RevId: 313781995

1 files changed, 56 insertions, 4 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index b739095b7..1d83b6840 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -201,6 +201,26 @@ func (d *dentry) DecRef() {
 	d.inode.decRef()
 }
 
+// InotifyWithParent implements vfs.DentryImpl.InotifyWithParent.
+func (d *dentry) InotifyWithParent(events uint32, cookie uint32) {
+	if d.inode.isDir() {
+		events |= linux.IN_ISDIR
+	}
+
+	// The ordering below is important, Linux always notifies the parent first.
+	if d.parent != nil {
+		// Note that d.parent or d.name may be stale if there is a concurrent
+		// rename operation. Inotify does not provide consistency guarantees.
+		d.parent.inode.watches.Notify(d.name, events, cookie)
+	}
+	d.inode.watches.Notify("", events, cookie)
+}
+
+// Watches implements vfs.DentryImpl.Watches.
+func (d *dentry) Watches() *vfs.Watches {
+	return &d.inode.watches
+}
+
 // inode represents a filesystem object.
 type inode struct {
 	// fs is the owning filesystem. fs is immutable.
@@ -236,6 +256,9 @@ type inode struct {
 	// Advisory file locks, which lock at the inode level.
 	locks lock.FileLocks
 
+	// Inotify watches for this inode.
+	watches vfs.Watches
+
 	impl interface{} // immutable
 }
 
@@ -257,6 +280,7 @@ func (i *inode) init(impl interface{}, fs *filesystem, creds *auth.Credentials,
 	i.ctime = now
 	i.mtime = now
 	// i.nlink initialized by caller
+	i.watches = vfs.Watches{}
 	i.impl = impl
 }
 
@@ -307,6 +331,7 @@ func (i *inode) tryIncRef() bool {
 
 func (i *inode) decRef() {
 	if refs := atomic.AddInt64(&i.refs, -1); refs == 0 {
+		i.watches.HandleDeletion()
 		if regFile, ok := i.impl.(*regularFile); ok {
 			// Release memory used by regFile to store data. Since regFile is
 			// no longer usable, we don't need to grab any locks or update any
@@ -628,8 +653,12 @@ func (fd *fileDescription) filesystem() *filesystem {
 	return fd.vfsfd.Mount().Filesystem().Impl().(*filesystem)
 }
 
+func (fd *fileDescription) dentry() *dentry {
+	return fd.vfsfd.Dentry().Impl().(*dentry)
+}
+
 func (fd *fileDescription) inode() *inode {
-	return fd.vfsfd.Dentry().Impl().(*dentry).inode
+	return fd.dentry().inode
 }
 
 // Stat implements vfs.FileDescriptionImpl.Stat.
@@ -642,7 +671,16 @@ func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linu
 // SetStat implements vfs.FileDescriptionImpl.SetStat.
 func (fd *fileDescription) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
 	creds := auth.CredentialsFromContext(ctx)
-	return fd.inode().setStat(ctx, creds, &opts.Stat)
+	d := fd.dentry()
+	if err := d.inode.setStat(ctx, creds, &opts.Stat); err != nil {
+		return err
+	}
+
+	// Generate inotify events.
+	if ev := vfs.InotifyEventFromStatMask(opts.Stat.Mask); ev != 0 {
+		d.InotifyWithParent(ev, 0)
+	}
+	return nil
 }
 
 // Listxattr implements vfs.FileDescriptionImpl.Listxattr.
@@ -657,12 +695,26 @@ func (fd *fileDescription) Getxattr(ctx context.Context, opts vfs.GetxattrOption
 
 // Setxattr implements vfs.FileDescriptionImpl.Setxattr.
 func (fd *fileDescription) Setxattr(ctx context.Context, opts vfs.SetxattrOptions) error {
-	return fd.inode().setxattr(auth.CredentialsFromContext(ctx), &opts)
+	d := fd.dentry()
+	if err := d.inode.setxattr(auth.CredentialsFromContext(ctx), &opts); err != nil {
+		return err
+	}
+
+	// Generate inotify events.
+	d.InotifyWithParent(linux.IN_ATTRIB, 0)
+	return nil
 }
 
 // Removexattr implements vfs.FileDescriptionImpl.Removexattr.
 func (fd *fileDescription) Removexattr(ctx context.Context, name string) error {
-	return fd.inode().removexattr(auth.CredentialsFromContext(ctx), name)
+	d := fd.dentry()
+	if err := d.inode.removexattr(auth.CredentialsFromContext(ctx), name); err != nil {
+		return err
+	}
+
+	// Generate inotify events.
+	d.InotifyWithParent(linux.IN_ATTRIB, 0)
+	return nil
 }
 
 // NewMemfd creates a new tmpfs regular file and file description that can back