libs: Do not rely on nftw for detecting the validity of plugin path

test_plugin.c:test_create_all_from_dir with non existing path fails on
cygwin. An error is expected but bt_plugin_find_all_from_dir returns
success.

The cygwin implementation of nftw is not posix compliant regarding
returning ENOENT on non-existent path. [1] [2]

The cygwin implementation of nftw does not return ENOENT on non-existent
path. Instead, the non-existent path is passed through the fn function
(nftw_append_all_from_dir) and the flag is set to FTW_NS.

Since we are "discovering" plugins, nftw_append_all_from_dir does not
error out on FTW_NS and simply skip the file.

The proposed solution is to stat() the provided path and validate that
no errors occur before using nftw().

[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/nftw.html
[2] https://cygwin.com/ml/cygwin/2019-06/msg00185.html

Change-Id: Ia7c88dbab5b16affbdb8ce1dbe261b03635727cc
Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1520
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>

diff --git a/src/lib/plugin/plugin.c b/src/lib/plugin/plugin.c
index 7caf362e0a4f8c2ba6910c8b159244e05fd7dd5c..1cef5123b071810d54ee1ea76882a1cfb3b963d9 100644 (file)
--- a/src/lib/plugin/plugin.c
+++ b/src/lib/plugin/plugin.c
@@ -485,10 +485,28 @@ enum bt_plugin_status bt_plugin_create_append_all_from_dir(
        int nftw_flags = FTW_PHYS;
        int ret;
        enum bt_plugin_status status;
+       struct stat sb;
 
        BT_ASSERT(plugin_set);
        BT_ASSERT(path);
        BT_ASSERT(strlen(path) < PATH_MAX);
+
+       /*
+        * Make sure that path exists and is accessible.
+        * This is necessary since Cygwin implementation of nftw() is not POSIX
+        * compliant. Cygwin nftw() implementation does not fail on non-existent
+        * path with ENOENT. Instead, it flags the directory as FTW_NS. FTW_NS during
+        * nftw_append_all_from_dir is not treated as an error since we are
+        * traversing the tree for plugin discovery.
+        */
+       if (stat(path, &sb)) {
+               BT_LOGW_ERRNO("Cannot open directory",
+                       ": path=\"%s\", recurse=%d",
+                       path, recurse);
+               status = BT_PLUGIN_STATUS_ERROR;
+               goto end;
+       }
+
        pthread_mutex_lock(&append_all_from_dir_info.lock);
        append_all_from_dir_info.plugin_set = plugin_set;
        append_all_from_dir_info.recurse = recurse;