Fix: ctf: notif-iter: error on empty events (0 bits of data)

Do not create an event which consumed 0 bits of data stream: log an
error and return without creating it. We keep the buffer position at the
beginning of the last decoded event header, and we compare to the
current buffer position: if they are the same, then we consumed 0 bits
of data. It is possible, when we compare, that notit->buf.last_eh_at is
-1ULL (reset when requesting bytes from medium): in this case, we know
we requested bytes anyway, which means we consumed something to get to
this starvation point, thus the event is not empty.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/plugins/ctf/common/notif-iter/notif-iter.c b/plugins/ctf/common/notif-iter/notif-iter.c
index 7d570a63acf93267fa79a3c424b8768872aa00a6..4ac971a9928eadcae7894772590571a8bc947dae 100644 (file)
--- a/plugins/ctf/common/notif-iter/notif-iter.c
+++ b/plugins/ctf/common/notif-iter/notif-iter.c
@@ -211,6 +211,9 @@ struct bt_ctf_notif_iter {
 
                /* Current position from addr (bits) */
                size_t at;
+
+               /* Position of the last event header from addr (bits) */
+               size_t last_eh_at;
        } buf;
 
        /* Binary type reader */
@@ -477,6 +480,7 @@ enum bt_ctf_notif_iter_status request_medium_bytes(
 
                /* Restart at the beginning of the new medium buffer */
                notit->buf.at = 0;
+               notit->buf.last_eh_at = -1ULL;
 
                /* New medium buffer size */
                notit->buf.sz = buffer_sz;
@@ -1252,6 +1256,9 @@ enum bt_ctf_notif_iter_status read_event_header_begin_state(
        enum bt_ctf_notif_iter_status status = BT_CTF_NOTIF_ITER_STATUS_OK;
        struct bt_ctf_field_type *event_header_type = NULL;
 
+       /* Reset the position of the last event header */
+       notit->buf.last_eh_at = notit->buf.at;
+
        /* Check if we have some content left */
        if (notit->cur_content_size >= 0) {
                if (packet_at(notit) == notit->cur_content_size) {
@@ -1782,6 +1789,7 @@ void bt_ctf_notif_iter_reset(struct bt_ctf_notif_iter *notit)
        notit->buf.addr = NULL;
        notit->buf.sz = 0;
        notit->buf.at = 0;
+       notit->buf.last_eh_at = -1ULL;
        notit->buf.packet_offset = 0;
        notit->state = STATE_INIT;
        notit->cur_content_size = -1;
@@ -2962,9 +2970,17 @@ void notify_event(struct bt_ctf_notif_iter *notit,
                struct bt_clock_class_priority_map *cc_prio_map,
                struct bt_notification **notification)
 {
-       struct bt_ctf_event *event;
+       struct bt_ctf_event *event = NULL;
        struct bt_notification *ret = NULL;
 
+       /* Make sure that the event contains at least one bit of data */
+       if (notit->buf.at == notit->buf.last_eh_at) {
+               BT_LOGE("Cannot create empty event with 0 bits of data: "
+                       "notit-addr=%p, packet-cur=%zu",
+                       notit, packet_at(notit));
+               goto end;
+       }
+
        /* Create event */
        event = create_event(notit);
        if (!event) {