Update comments for synthetic gofer files in vfs2.

PiperOrigin-RevId: 309966538

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -686,6 +686,8 @@ func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 	return fs.doCreateAt(ctx, rp, false /* dir */, func(parent *dentry, name string) error {
 		creds := rp.Credentials()
 		_, err := parent.file.mknod(ctx, name, (p9.FileMode)(opts.Mode), opts.DevMajor, opts.DevMinor, (p9.UID)(creds.EffectiveKUID), (p9.GID)(creds.EffectiveKGID))
+		// If the gofer does not allow creating a socket or pipe, create a
+		// synthetic one, i.e. one that is kept entirely in memory.
 		if err == syserror.EPERM {
 			switch opts.Mode.FileType() {
 			case linux.S_IFSOCK:

pkg/sentry/fsimpl/gofer/gofer.go

@@ -496,10 +496,8 @@ type dentry struct {
 	// file is the unopened p9.File that backs this dentry. file is immutable.
 	//
 	// If file.isNil(), this dentry represents a synthetic file, i.e. a file
-	// that does not exist on the remote filesystem. As of this writing, this
-	// is only possible for a directory created with
-	// MkdirOptions.ForSyntheticMountpoint == true.
-	// TODO(gvisor.dev/issue/1476): Support synthetic sockets (and pipes).
+	// that does not exist on the remote filesystem. As of this writing, the
+	// only files that can be synthetic are sockets, pipes, and directories.
 	file p9file
 
 	// If deleted is non-zero, the file represented by this dentry has been