libdwfl_stacktrace [9/12]: add dwflst_tracker_find_pid

Changes for v6:

- Minor fixes as requested.

Changes for v4:

- Separate out libdwfl_stacktrace, as requested.

Changes for v2:

- Add locking for dwfltab.

* * *

New function that retrieves the Dwfl for a particular PID, or,
if the Dwfl is absent, creates it via a provided callback
and adds it to the table later, when the PID is confirmed
via dwfl_attach_state.

* libdwfl_stacktrace/libdwfl_stacktrace.h (dwflst_tracker_find_pid):
  New function.
* libdwfl_stacktrace/dwfl_process_tracker.c (dwflst_tracker_find_pid):
  New function; find a Dwfl in the dwfltab or create one using the
  provided callback.  The newly created Dwfl will be added to the
  dwfltab automatically when its pid is confirmed by a call to
  dwfl_attach_state.
* libdw/libdw.map: Add dwflst_tracker_find_pid.

3 files changed, 41 insertions, 0 deletions

diff --git a/libdw/libdw.map b/libdw/libdw.map
index 46d0878a..688e415c 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -404,4 +404,5 @@ ELFUTILS_0.193_EXPERIMENTAL {
     dwflst_tracker_cache_elf;
     dwflst_module_gettracker;
     dwflst_tracker_linux_proc_find_elf;
+    dwflst_tracker_find_pid;
 };
diff --git a/libdwfl_stacktrace/dwflst_process_tracker.c b/libdwfl_stacktrace/dwflst_process_tracker.c
index c0678cb8..779f25f0 100644
--- a/libdwfl_stacktrace/dwflst_process_tracker.c
+++ b/libdwfl_stacktrace/dwflst_process_tracker.c
@@ -67,6 +67,32 @@ Dwfl *dwflst_tracker_dwfl_begin (Dwflst_Process_Tracker *tracker)
   return dwfl;
 }
 
+Dwfl *dwflst_tracker_find_pid (Dwflst_Process_Tracker *tracker,
+			       pid_t pid,
+			       Dwfl *(*callback) (Dwflst_Process_Tracker *,
+						  pid_t, void *),
+			       void *arg)
+{
+  Dwfl *dwfl = NULL;
+
+  rwlock_rdlock (tracker->dwfltab_lock);
+  dwflst_tracker_dwfl_info *ent
+    = dwflst_tracker_dwfltab_find(&tracker->dwfltab, pid);
+  rwlock_unlock (tracker->dwfltab_lock);
+
+  if (ent != NULL && !ent->invalid)
+    dwfl = ent->dwfl;
+  if (dwfl == NULL && callback != NULL)
+    dwfl = callback(tracker, pid, arg);
+  if (dwfl != NULL)
+    {
+      assert (dwfl->tracker == tracker);
+      /* XXX: dwfl added to dwfltab when dwfl->process set in dwfl_attach_state.
+         Prior to that, the pid is not confirmed. */
+    }
+
+  return dwfl;
+}
 
 void
 internal_function
diff --git a/libdwfl_stacktrace/libdwfl_stacktrace.h b/libdwfl_stacktrace/libdwfl_stacktrace.h
index 286409b8..064c97b2 100644
--- a/libdwfl_stacktrace/libdwfl_stacktrace.h
+++ b/libdwfl_stacktrace/libdwfl_stacktrace.h
@@ -81,6 +81,20 @@ extern bool dwflst_tracker_cache_elf (Dwflst_Process_Tracker *tracker,
 				      Elf *elf, int fd)
   __nonnull_attribute__ (1, 2);
 
+/* Find the Dwfl corresponding to PID.  If CALLBACK is non-NULL and
+   the Dwfl has not been created, invoke CALLBACK, which should return
+   a Dwfl linked to the tracker (or NULL if Dwfl creation also fails).
+   The Dwfl will be automatically added to the tracker's internal
+   table when its pid is confirmed by calling dwfl_attach_state.
+   Returns NULL if Dwfl was not found and callback failed.  */
+extern Dwfl *dwflst_tracker_find_pid (Dwflst_Process_Tracker *tracker,
+				      pid_t pid,
+				      Dwfl *(*callback) (Dwflst_Process_Tracker *tracker,
+							 pid_t pid,
+							 void *arg),
+				      void *arg)
+  __nonnull_attribute__ (1);
+
 /* For implementing a find_elf callback based on the prior two functions.
    Returns the Dwflst_Process_Tracker corresponding to MOD.  */
 extern Dwflst_Process_Tracker *dwflst_module_gettracker (Dwfl_Module *mod);