python: improve string handling

This adds ev.str_field('foo') as a non-raising
version of str(ev['foo']) that this patch also
enables. A new C function is necessary because
str(ev['foo'].data) may contain the NUL bytes
that should have terminated the C strings.

Suggested-by: Pierre Tardy <tardyp@gmail.com>
Acked-by: Darren Hart <dvhltc@us.ibm.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

2 files changed, 34 insertions, 0 deletions

diff --git a/ctracecmd.i b/ctracecmd.i
index 9569419..624fb63 100644
--- a/ctracecmd.i
+++ b/ctracecmd.i
@@ -69,6 +69,32 @@ static PyObject *py_field_get_data(struct format_field *f, struct record *r)
         return PyBuffer_FromMemory((char *)r->data + f->offset, f->size);
 }
 
+static PyObject *py_field_get_str(struct format_field *f, struct record *r)
+{
+        if (!strncmp(f->type, "__data_loc ", 11)) {
+                unsigned long long val;
+                int offset;
+
+                if (pevent_read_number_field(f, r->data, &val)) {
+                        PyErr_SetString(PyExc_TypeError,
+                                        "Field is not a valid number");
+                        return NULL;
+                }
+
+                /*
+                 * The actual length of the dynamic array is stored
+                 * in the top half of the field, and the offset
+                 * is in the bottom half of the 32 bit field.
+                 */
+                offset = val & 0xffff;
+
+                return PyString_FromString((char *)r->data + offset);
+        }
+
+        return PyString_FromStringAndSize((char *)r->data + f->offset,
+                                strnlen((char *)r->data + f->offset, f->size));
+}
+
 static PyObject *py_format_get_keys(struct event_format *ef)
 {
         PyObject *list;
diff --git a/tracecmd.py b/tracecmd.py
index b14a3b9..ad80ccd 100644
--- a/tracecmd.py
+++ b/tracecmd.py
@@ -110,6 +110,11 @@ class Event(object):
             return None
         return val
 
+    def str_field(self, name):
+        f = pevent_find_any_field(self._format, name)
+        if f is None:
+            return None
+        return py_field_get_str(f, self._record)
 
 class TraceSeq(object):
     def __init__(self, trace_seq):
@@ -138,6 +143,9 @@ class Field(object):
         return val
     __int__ = __long__
 
+    def __str__(self):
+        return py_field_get_str(self._field, self._record)
+
 class PEvent(object):
     def __init__(self, pevent):
         self._pevent = pevent