[PATCH v2 1/4] libtracefs: Add tracefs_list_pop() to remove the last item

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Add a way to remove the last item of a string list. This will be needed to
revert changes made to the new tracefs_synth structure that will have more
than one tracefs_list char ** that must be the same size. If one is
successfully updated, but the next one fails, the first one needs to be
reverted.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/tracefs.h   |  1 +
 src/tracefs-utils.c | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/tracefs.h b/include/tracefs.h
index 2649417654b1..4dd77b9c4119 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -66,6 +66,7 @@ int tracefs_error_clear(struct tracefs_instance *instance);
 void tracefs_list_free(char **list);
 char **tracefs_list_add(char **list, const char *string);
 int tracefs_list_size(char **list);
+int tracefs_list_pop(char **list);
 
 /**
  * tracefs_trace_on_get_fd - Get a file descriptor of "tracing_on" in given instance
diff --git a/src/tracefs-utils.c b/src/tracefs-utils.c
index 600cdf2acefc..63bb413298fe 100644
--- a/src/tracefs-utils.c
+++ b/src/tracefs-utils.c
@@ -448,6 +448,32 @@ char **tracefs_list_add(char **list, const char *string)
 	return list;
 }
 
+/**
+ * tracefs_list_pop - Removes the last string added
+ * @list: The list to remove the last event from
+ *
+ * Returns 0 on success, -1 on error.
+ * Returns 1 if the list is empty or NULL.
+ */
+int tracefs_list_pop(char **list)
+{
+	unsigned long size;
+
+	if (!list || list[0])
+		return 1;
+
+	list--;
+	size = *(unsigned long *)list;
+	/* size must be greater than zero */
+	if (!size)
+		return -1;
+	size--;
+	*list = (char *)size;
+	list++;
+	list[size] = '\0';
+	return 0;
+}
+
 /**
  * tracefs_list_size - Return the number of strings in the list
  * @list: The list to determine the size.
-- 
2.30.2