[lttng-dev] [PATCH babeltrace] Fix: lttng-live flush when output to file

[Jérémie Galarneau]

Merged in master and stable-1.3. Thanks!

Jérémie

On Tue, Apr 19, 2016 at 6:42 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> When the standard output is redirected to a file, we need to flush the
> output between each packet, otherwise the stream buffering may keep us
> from seeing events for a while in a low-throughput trace.
>
> While we are there, document that lttng-live does now support the
> --output option in babeltrace 1.x.
>
> Fixes #1010
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
>  doc/babeltrace.1                       |  3 ++-
>  formats/lttng-live/lttng-live-comm.c   | 13 ++++++++++++-
>  formats/lttng-live/lttng-live-plugin.c |  6 ++++++
>  formats/lttng-live/lttng-live.h        |  7 +++++++
>  4 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/doc/babeltrace.1 b/doc/babeltrace.1
> index f783105..cee9f7b 100644
> --- a/doc/babeltrace.1
> +++ b/doc/babeltrace.1
> @@ -100,7 +100,8 @@ babeltrace-log(1), lttng(1), lttng-ust(3), lttng-sessiond(8)
>  .SH "BUGS"
>
>  .PP
> -No known bugs at this point.
> +The lttng-live plugin does not honor the the "--output" command line
> +option.
>
>  If you encounter any issues or usability problem, please report it on
>  our mailing list <lttng-dev at lists.lttng.org> to help improve this
> diff --git a/formats/lttng-live/lttng-live-comm.c b/formats/lttng-live/lttng-live-comm.c
> index cea50ff..729df6f 100644
> --- a/formats/lttng-live/lttng-live-comm.c
> +++ b/formats/lttng-live/lttng-live-comm.c
> @@ -246,7 +246,7 @@ void print_session_list(GPtrArray *session_list, const char *path)
>
>         for (i = 0; i < session_list->len; i++) {
>                 relay_session = g_ptr_array_index(session_list, i);
> -               fprintf(stdout, "%s/host/%s/%s (timer = %u, "
> +               fprintf(LTTNG_LIVE_OUTPUT_FP, "%s/host/%s/%s (timer = %u, "
>                                 "%u stream(s), %u client(s) connected)\n",
>                                 path, relay_session->hostname,
>                                 relay_session->name, relay_session->timer,
> @@ -649,6 +649,17 @@ retry:
>                 ret = -1;
>                 goto end;
>         }
> +
> +       /*
> +        * Flush the output between attempt to grab a packet, thus
> +        * ensuring we flush at least at the periodical timer period.
> +        * This is useful when the output is redirected to a file.
> +        */
> +       if (fflush(LTTNG_LIVE_OUTPUT_FP) < 0) {
> +               perror("fflush");
> +               goto error;
> +       }
> +
>         cmd.cmd = htobe32(LTTNG_VIEWER_GET_PACKET);
>         cmd.data_size = htobe64(sizeof(rq));
>         cmd.cmd_version = htobe32(0);
> diff --git a/formats/lttng-live/lttng-live-plugin.c b/formats/lttng-live/lttng-live-plugin.c
> index bf71b2b..771801c 100644
> --- a/formats/lttng-live/lttng-live-plugin.c
> +++ b/formats/lttng-live/lttng-live-plugin.c
> @@ -292,6 +292,12 @@ struct bt_trace_descriptor *lttng_live_open_trace(const char *path, int flags,
>         pos->parent.rw_table = NULL;
>         pos->parent.event_cb = NULL;
>         pos->parent.trace = &pos->trace_descriptor;
> +       /*
> +        * Since we do *everything* in this function, we are skipping
> +        * the output plugin handling that is part of Babeltrace 1.x.
> +        * Therefore, don't expect the --output cmd line option to work.
> +        * This limits the output of lttng-live to stderr and stdout.
> +        */
>         if (lttng_live_open_trace_read(path) < 0) {
>                 goto error;
>         }
> diff --git a/formats/lttng-live/lttng-live.h b/formats/lttng-live/lttng-live.h
> index 553cd34..e00a51e 100644
> --- a/formats/lttng-live/lttng-live.h
> +++ b/formats/lttng-live/lttng-live.h
> @@ -32,6 +32,13 @@
>  #define LTTNG_LIVE_MAJOR                       2
>  #define LTTNG_LIVE_MINOR                       4
>
> +/*
> + * The lttng-live output file pointer is currently hardcoded to stdout,
> + * and is expected to be hardcoded to this by fflush() performed between
> + * each packet.
> + */
> +#define LTTNG_LIVE_OUTPUT_FP                   stdout
> +
>  struct lttng_live_ctx {
>         char traced_hostname[MAXNAMLEN];
>         char session_name[MAXNAMLEN];
> --
> 2.1.4
>



-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com