Implement $PATH binary searching function for userspace-probe

This is needed to allow the user to simply provide the name of a
executable present in the $PATH for the current shell.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng/commands/enable_events.c b/src/bin/lttng/commands/enable_events.c
index e90db88d1ff86398104d1a70b4ea162f6e390c50..f4403c25e8d30a566553dd40f23ff61d5f63504d 100644 (file)
--- a/src/bin/lttng/commands/enable_events.c
+++ b/src/bin/lttng/commands/enable_events.c
@@ -28,8 +28,11 @@
 
 #include <common/sessiond-comm/sessiond-comm.h>
 #include <common/compat/string.h>
+#include <common/compat/getenv.h>
 #include <common/string-utils/string-utils.h>
+#include <common/utils.h>
 
+#include <lttng/constant.h>
 /* Mi dependancy */
 #include <common/mi-lttng.h>
 
@@ -173,6 +176,117 @@ end:
        return ret;
 }
 
+/*
+ * Walk the directories in the PATH environment variable to find the target
+ * binary passed as parameter.
+ *
+ * On success, the full path of the binary is copied in binary_full_path out
+ * parameter. This buffer is allocated by the caller and must be at least
+ * LTTNG_PATH_MAX bytes long.
+ * On failure, returns -1;
+ */
+static int walk_command_search_path(const char *binary, char *binary_full_path)
+{
+       char *tentative_binary_path = NULL;
+       char *command_search_path = NULL;
+       char *curr_search_dir_end = NULL;
+       char *curr_search_dir = NULL;
+       struct stat stat_output;
+       int ret = 0;
+
+       command_search_path = lttng_secure_getenv("PATH");
+       if (!command_search_path) {
+               ret = -1;
+               goto end;
+       }
+
+       /*
+        * Duplicate the $PATH string as the char pointer returned by getenv() should
+        * not be modified.
+        */
+       command_search_path = strdup(command_search_path);
+       if (!command_search_path) {
+               ret = -1;
+               goto end;
+       }
+
+       /*
+        * This char array is used to concatenate path to binary to look for
+        * the binary.
+        */
+       tentative_binary_path = zmalloc(LTTNG_PATH_MAX * sizeof(char));
+       if (!tentative_binary_path) {
+               ret = -1;
+               goto alloc_error;
+       }
+
+       curr_search_dir = command_search_path;
+       do {
+               /*
+                * Split on ':'. The return value of this call points to the
+                * matching character.
+                */
+               curr_search_dir_end = strchr(curr_search_dir, ':');
+               if (curr_search_dir_end != NULL) {
+                       /*
+                        * Add a NULL byte to the end of the first token so it
+                        * can be used as a string.
+                        */
+                       curr_search_dir_end[0] = '\0';
+               }
+
+               /* Empty the tentative path */
+               memset(tentative_binary_path, 0, LTTNG_PATH_MAX * sizeof(char));
+
+               /*
+                * Build the tentative path to the binary using the current
+                * search directory and the name of the binary.
+                */
+               ret = snprintf(tentative_binary_path, LTTNG_PATH_MAX, "%s/%s",
+                               curr_search_dir, binary);
+               if (ret < 0) {
+                       goto free_binary_path;
+               }
+               if (ret < LTTNG_PATH_MAX) {
+                        /*
+                         * Use STAT(2) to see if the file exists.
+                        */
+                       ret = stat(tentative_binary_path, &stat_output);
+                       if (ret == 0) {
+                               /*
+                                * Verify that it is a regular file or a
+                                * symlink and not a special file (e.g.
+                                * device).
+                                */
+                               if (S_ISREG(stat_output.st_mode)
+                                               || S_ISLNK(stat_output.st_mode)) {
+                                       /*
+                                        * Found a match, set the out parameter
+                                        * and return success.
+                                        */
+                                       ret = lttng_strncpy(binary_full_path,
+                                                       tentative_binary_path,
+                                                       LTTNG_PATH_MAX);
+                                       if (ret == -1) {
+                                               ERR("Source path does not fit "
+                                                       "in destination buffer.");
+                                       }
+                                       goto free_binary_path;
+                               }
+                       }
+               }
+               /* Go to the next entry in the $PATH variable. */
+               curr_search_dir = curr_search_dir_end + 1;
+       } while (curr_search_dir_end != NULL);
+
+free_binary_path:
+       free(tentative_binary_path);
+alloc_error:
+       free(command_search_path);
+end:
+       return ret;
+}
+
 /*
  * Maps LOG4j loglevel from string to value
  */