libfs: separating closing a file descriptor from releasing a reference to the file itself

lib/libfs/context.c

@@ -145,13 +145,15 @@ static enum fs_status handle_event(struct fs_context *ctx, xpc_msg_t *msg)
 {
 	switch (msg->msg_event) {
 	case KERN_MSG_EVENT_CONNECTION:
-		kern_logf("received connection");
+		kern_tracef("received connection");
 		break;
 	case KERN_MSG_EVENT_DISCONNECTION: {
+		kern_tracef("received disconnect");
 		struct fs_file *f
 			= fs_context_get_file(ctx, msg->msg_sender.e_port);
 		if (f) {
 			fs_context_close_file(ctx, f);
+			fs_context_unref_file(ctx, f);
 		}
 		break;
 	}
@@ -200,7 +202,14 @@ static enum fs_status handle_page_request_detach(
 	equeue_packet_page_request_t *packet,
 	struct file_mapping *mapping)
 {
+	if (!mapping) {
 		kern_logf(
+			"received DETACH request from VMO with no associated "
+		        "mapping");
+		return FS_ERR_INTERNAL_FAILURE;
+	}
+
+	kern_tracef(
 		"received page request (detach) for file %s",
 		mapping->m_file->f_dent->d_name);
 
@@ -216,7 +225,7 @@ static enum fs_status handle_page_request_detach(
 	kern_handle_close(mapping->m_vmo);
 	fs_context_free(ctx, mapping);
 
-	fs_context_close_file(ctx, f);
+	fs_context_unref_file(ctx, f);
 	return FS_SUCCESS;
 }
 
@@ -335,18 +344,26 @@ struct fs_file *fs_context_get_file(struct fs_context *ctx, unsigned long id)
 	return get_file(&ctx->ctx_filelist, id);
 }
 
-void fs_context_close_file(struct fs_context *ctx, struct fs_file *f)
+void fs_context_unref_file(struct fs_context *ctx, struct fs_file *f)
 {
 	if (f->f_ref > 1) {
-		kern_logf(
+		kern_tracef(
 			"reference to file '%s' has been closed",
 			f->f_dent->d_name);
 		f->f_ref--;
 		return;
 	}
 
-	kern_logf("file '%s' has been closed", f->f_dent->d_name);
+	kern_tracef("file '%s' has been closed", f->f_dent->d_name);
+	fs_context_free(ctx, f);
+}
+
+void fs_context_close_file(struct fs_context *ctx, struct fs_file *f)
+{
+	if (f->f_id) {
 		btree_delete(&ctx->ctx_filelist, &f->f_node);
+		f->f_id = 0;
+	}
 }
 
 static size_t get_first_path_component(const char *in, char *out, size_t max)

lib/libfs/include/fs/context.h

@@ -42,6 +42,7 @@ extern struct fs_file *fs_context_open_file(
 extern struct fs_file *fs_context_get_file(
 	struct fs_context *ctx,
 	unsigned long id);
+extern void fs_context_unref_file(struct fs_context *ctx, struct fs_file *f);
 extern void fs_context_close_file(struct fs_context *ctx, struct fs_file *f);
 
 extern enum fs_status fs_context_resolve_path(