From 46307ffe11537f48a43ff90f3b3b048eeea248f1 Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?=
 <jeremie.galarneau@efficios.com>
Date: Wed, 1 May 2019 10:50:55 -0400
Subject: [PATCH] Allow lttng_directory_handle to be moved
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Implement a "move" method (akin to C++'s move semantics) which allows
the transfer of the contents/ownership of a stack-allocated directory
handle to another object.

A moved directory handle must no longer be used after the "move"
operation. The original moved handle is invalidated in the hope
of catching erroneous uses of this API quickly.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 src/common/compat/directory-handle.c | 31 ++++++++++++++++++++++++++--
 src/common/compat/directory-handle.h | 12 +++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/src/common/compat/directory-handle.c b/src/common/compat/directory-handle.c
index 562a79287..6e04c6a3c 100644
--- a/src/common/compat/directory-handle.c
+++ b/src/common/compat/directory-handle.c
@@ -41,6 +41,8 @@ int _run_as_mkdir(const struct lttng_directory_handle *handle, const char *path,
 static
 int _run_as_mkdir_recursive(const struct lttng_directory_handle *handle,
 		const char *path, mode_t mode, uid_t uid, gid_t gid);
+static
+void lttng_directory_handle_invalidate(struct lttng_directory_handle *handle);
 
 #ifdef COMPAT_DIRFD
 
@@ -79,13 +81,15 @@ void lttng_directory_handle_fini(struct lttng_directory_handle *handle)
 {
 	int ret;
 
-	if (handle->dirfd == AT_FDCWD) {
-		return;
+	if (handle->dirfd == AT_FDCWD || handle->dirfd == -1) {
+		goto end;
 	}
 	ret = close(handle->dirfd);
 	if (ret == -1) {
 		PERROR("Failed to close directory file descriptor of directory handle");
 	}
+end:
+	lttng_directory_handle_invalidate(handle);
 }
 
 LTTNG_HIDDEN
@@ -106,6 +110,12 @@ int lttng_directory_handle_copy(const struct lttng_directory_handle *handle,
 	return ret;
 }
 
+static
+void lttng_directory_handle_invalidate(struct lttng_directory_handle *handle)
+{
+	handle->dirfd = -1;
+}
+
 static
 int lttng_directory_handle_stat(const struct lttng_directory_handle *handle,
 		const char *path, struct stat *st)
@@ -241,6 +251,7 @@ LTTNG_HIDDEN
 void lttng_directory_handle_fini(struct lttng_directory_handle *handle)
 {
 	free(handle->base_path);
+	lttng_directory_handle_invalidate(handle);
 }
 
 LTTNG_HIDDEN
@@ -251,6 +262,12 @@ int lttng_directory_handle_copy(const struct lttng_directory_handle *handle,
 	return new_copy->base_path ? 0 : -1;
 }
 
+static
+void lttng_directory_handle_invalidate(struct lttng_directory_handle *handle)
+{
+	handle->base_path = NULL;
+}
+
 static
 int get_full_path(const struct lttng_directory_handle *handle,
 		const char *subdirectory, char *fullpath, size_t size)
@@ -385,6 +402,16 @@ end:
 }
 
 /* Common implementation. */
+LTTNG_HIDDEN
+struct lttng_directory_handle
+lttng_directory_handle_move(struct lttng_directory_handle *original)
+{
+	const struct lttng_directory_handle tmp = *original;
+
+	lttng_directory_handle_invalidate(original);
+	return tmp;
+}
+
 static
 int create_directory_recursive(const struct lttng_directory_handle *handle,
 		const char *path, mode_t mode)
diff --git a/src/common/compat/directory-handle.h b/src/common/compat/directory-handle.h
index ceebc941e..dad4299ca 100644
--- a/src/common/compat/directory-handle.h
+++ b/src/common/compat/directory-handle.h
@@ -62,6 +62,18 @@ LTTNG_HIDDEN
 int lttng_directory_handle_copy(const struct lttng_directory_handle *handle,
 		struct lttng_directory_handle *new_copy);
 
+/*
+ * Move a directory handle. The original directory handle may no longer be
+ * used after this call. This call cannot fail; directly assign the
+ * return value to the new directory handle.
+ *
+ * It is safe (but unnecessary) to call lttng_directory_handle_fini on the
+ * original handle.
+ */
+LTTNG_HIDDEN
+struct lttng_directory_handle
+lttng_directory_handle_move(struct lttng_directory_handle *original);
+
 /*
  * Release the resources of a directory handle.
  */
-- 
2.34.1