[PATCH v11 7/7] monitor: Clean up fd sets on monitor disconnect

[Corey Bryant <coreyb@xxxxxxxxxxxxxxxxxx>]

Fd sets are shared by all monitor connections.  Fd sets are considered
to be in use while at least one monitor is connected.  When the last
monitor disconnects, all fds that are members of an fd set with no
outstanding dup references are closed.  This prevents any fd leakage
associated with a client disconnect prior to using a passed fd.

Signed-off-by: Corey Bryant <coreyb@xxxxxxxxxxxxxxxxxx>
---
v5:
 -This patch is new in v5.
 -This support addresses concerns from v4 regarding fd leakage
  if the client disconnects unexpectedly. (eblake@xxxxxxxxxx,
  kwolf@xxxxxxxxxx, dberrange@xxxxxxxxxx)

v6:
 -No changes

v7:
 -Removed monitor_fdsets_set_in_use() function since we now use
  mon_refcount to determine if fdsets are in use.
 -Added monitor_fdsets_cleanup() function, and increment/decrement
  of mon_refcount when monitor connects/disconnects.

v8:
 -Use camel case for structures. (stefanha@xxxxxxxxxxxxxxxxxx)

v9:
 -Define mon_refcount and add corresponding logic to
  monitor_fdset_cleanup here rather than earlier patch.
  (kwolf@xxxxxxxxxx)

v10-v11:
 -No changes

 monitor.c |   23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/monitor.c b/monitor.c
index c2652b4..2bcc7bc 100644
--- a/monitor.c
+++ b/monitor.c
@@ -200,6 +200,7 @@ struct Monitor {
 
 static QLIST_HEAD(mon_list, Monitor) mon_list;
 static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
+static int mon_refcount;
 
 static mon_cmd_t mon_cmds[];
 static mon_cmd_t info_cmds[];
@@ -2391,7 +2392,8 @@ static void monitor_fdset_cleanup(MonFdset *mon_fdset)
     MonFdsetFd *mon_fdset_fd_next;
 
     QLIST_FOREACH_SAFE(mon_fdset_fd, &mon_fdset->fds, next, mon_fdset_fd_next) {
-        if (mon_fdset_fd->removed) {
+        if (mon_fdset_fd->removed ||
+                (QLIST_EMPTY(&mon_fdset->dup_fds) && mon_refcount == 0)) {
             close(mon_fdset_fd->fd);
             g_free(mon_fdset_fd->opaque);
             QLIST_REMOVE(mon_fdset_fd, next);
@@ -2405,6 +2407,16 @@ static void monitor_fdset_cleanup(MonFdset *mon_fdset)
     }
 }
 
+static void monitor_fdsets_cleanup(void)
+{
+    MonFdset *mon_fdset;
+    MonFdset *mon_fdset_next;
+
+    QLIST_FOREACH_SAFE(mon_fdset, &mon_fdsets, next, mon_fdset_next) {
+        monitor_fdset_cleanup(mon_fdset);
+    }
+}
+
 AddfdInfo *qmp_add_fd(bool has_fdset_id, int64_t fdset_id, bool has_opaque,
                       const char *opaque, Error **errp)
 {
@@ -4821,9 +4833,12 @@ static void monitor_control_event(void *opaque, int event)
         data = get_qmp_greeting();
         monitor_json_emitter(mon, data);
         qobject_decref(data);
+        mon_refcount++;
         break;
     case CHR_EVENT_CLOSED:
         json_message_parser_destroy(&mon->mc->parser);
+        mon_refcount--;
+        monitor_fdsets_cleanup();
         break;
     }
 }
@@ -4864,6 +4879,12 @@ static void monitor_event(void *opaque, int event)
             readline_show_prompt(mon->rs);
         }
         mon->reset_seen = 1;
+        mon_refcount++;
+        break;
+
+    case CHR_EVENT_CLOSED:
+        mon_refcount--;
+        monitor_fdsets_cleanup();
         break;
     }
 }
-- 
1.7.10.4

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