Fix: event-notifier: do not flush packet if it only contains subbuf header

This poll behavior returns POLLIN in situations where there is
actually no event to read, which causes read to block when it
should not.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I59e56cd4da9907b6f9ccdc14c6037f0f72e4505e

diff --git a/src/lttng-abi.c b/src/lttng-abi.c
index 1b08b3b7412270ff2199ab3d3bde1e379ca23370..09e437884c8e54971dad9597d6f517cb8cf660fc 100644 (file)
--- a/src/lttng-abi.c
+++ b/src/lttng-abi.c
@@ -933,6 +933,7 @@ unsigned int lttng_event_notifier_group_notif_poll(struct file *filp,
        const struct lib_ring_buffer_config *config = &chan->backend.config;
        int finalized, disabled;
        unsigned long consumed, offset;
+       size_t subbuffer_header_size = config->cb.subbuffer_header_size();
 
        if (filp->f_mode & FMODE_READ) {
                poll_wait_set_exclusive(wait);
@@ -960,7 +961,7 @@ retry:
                        /*
                         * If there is a non-empty subbuffer, flush and try again.
                         */
-                       if (subbuf_offset(offset, chan) != 0) {
+                       if (subbuf_offset(offset, chan) > subbuffer_header_size) {
                                lib_ring_buffer_switch_remote(buf);
                                goto retry;
                        }