scd: Fix DEVINFO, allowing no clients which watch the change.

* scd/app.c [POSIX] (struct mrsw_lock): Add notify_watchers.
(card_list_signal): Only when watchers wait, kick by write(2).
(card_list_wait): Increment/decrement notify_watchers field.

--

GnuPG-bug-id: 7151
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/scd/app.c b/scd/app.c
index 18c0b4eb8..da80f1561 100644
--- a/scd/app.c
+++ b/scd/app.c
@@ -59,6 +59,7 @@ struct mrsw_lock
   HANDLE the_event;
 #else
   int notify_pipe[2];
+  int notify_watchers;
 #endif
 };
 
@@ -381,7 +382,10 @@ card_list_signal (void)
     log_error ("SetEvent for card_list_signal failed: %s\n",
                w32_strerror (-1));
 #else
-  write (card_list_lock.notify_pipe[1], "", 1);
+  npth_mutex_lock (&card_list_lock.lock);
+  if (card_list_lock.notify_watchers)
+    write (card_list_lock.notify_pipe[1], "", 1);
+  npth_mutex_unlock (&card_list_lock.lock);
 #endif
 }
 
@@ -401,7 +405,7 @@ card_list_wait (ctrl_t ctrl)
   npth_mutex_lock (&card_list_lock.lock);
   card_list_lock.writer_active--;
   npth_cond_broadcast (&card_list_lock.cond);
-
+  card_list_lock.notify_watchers++;
   npth_mutex_unlock (&card_list_lock.lock);
 
   while (1)
@@ -449,7 +453,7 @@ card_list_wait (ctrl_t ctrl)
     }
 
   npth_mutex_lock (&card_list_lock.lock);
-
+  card_list_lock.notify_watchers--;
   card_list_lock.num_writers_waiting++;
   while (card_list_lock.num_readers_active
          || card_list_lock.writer_active)