[PATCH v2 2/3] trace: Add support for recorder back-end

[Christophe de Dinechin]

The recorder library provides support for low-cost continuous
recording of events, which can then be replayed. This makes it
possible to collect data "after the fact",for example to show the
events that led to a crash.

Recorder support in qemu is implemented using the existing tracing
interface. In addition, it is possible to individually enable
recorders that are not traces, although this is probably not
recommended.

HMP COMMAND:
The 'recorder' hmp command has been added, which supports two
sub-commands:
- recorder dump: Dump the current state of the recorder. You can
- recorder trace: Set traces using the recorder_trace_set() syntax.
  You can use "recorder trace help" to list all available recorders.

Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>
---
 configure                             |  5 +++
 hmp-commands.hx                       | 19 ++++++++--
 monitor/misc.c                        | 27 ++++++++++++++
 scripts/tracetool/backend/recorder.py | 51 +++++++++++++++++++++++++++
 trace/Makefile.objs                   |  2 ++
 trace/control.c                       |  7 ++++
 trace/recorder.c                      | 22 ++++++++++++
 trace/recorder.h                      | 34 ++++++++++++++++++
 util/module.c                         |  8 +++++
 9 files changed, 173 insertions(+), 2 deletions(-)
 create mode 100644 scripts/tracetool/backend/recorder.py
 create mode 100644 trace/recorder.c
 create mode 100644 trace/recorder.h

diff --git a/configure b/configure
index ae8737d5a2..130630b98f 100755
--- a/configure
+++ b/configure
@@ -7702,6 +7702,11 @@ fi
 if have_backend "log"; then
   echo "CONFIG_TRACE_LOG=y" >> $config_host_mak
 fi
+if have_backend "recorder"; then
+  echo "CONFIG_TRACE_RECORDER=y" >> $config_host_mak
+  # This is a bit brutal, but there is currently a bug in the makefiles
+  LIBS="$LIBS -lrecorder"
+fi
 if have_backend "ust"; then
   echo "CONFIG_TRACE_UST=y" >> $config_host_mak
 fi
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 60f395c276..565f518d4b 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -297,6 +297,22 @@ ERST
         .cmd        = hmp_trace_file,
     },
 
+SRST
+``trace-file on|off|flush``
+  Open, close, or flush the trace file.  If no argument is given, the
+  status of the trace file is displayed.
+ERST
+#endif
+
+#if defined(CONFIG_TRACE_RECORDER)
+    {
+        .name       = "recorder",
+        .args_type  = "op:s?,arg:F?",
+        .params     = "trace|dump [arg]",
+        .help       = "trace selected recorders or print recorder dump",
+        .cmd        = hmp_recorder,
+    },
+
 SRST
 ``trace-file on|off|flush``
   Open, close, or flush the trace file.  If no argument is given, the
@@ -1120,7 +1136,7 @@ ERST
 
 SRST
 ``dump-guest-memory [-p]`` *filename* *begin* *length*
-  \ 
+  \
 ``dump-guest-memory [-z|-l|-s|-w]`` *filename*
   Dump guest memory to *protocol*. The file can be processed with crash or
   gdb. Without ``-z|-l|-s|-w``, the dump format is ELF.
@@ -1828,4 +1844,3 @@ ERST
         .sub_table  = hmp_info_cmds,
         .flags      = "p",
     },
-
diff --git a/monitor/misc.c b/monitor/misc.c
index 89bb970b00..0094b1860f 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -61,6 +61,9 @@
 #ifdef CONFIG_TRACE_SIMPLE
 #include "trace/simple.h"
 #endif
+#ifdef CONFIG_TRACE_RECORDER
+#include "trace/recorder.h"
+#endif
 #include "exec/memory.h"
 #include "exec/exec-all.h"
 #include "qemu/option.h"
@@ -227,6 +230,30 @@ static void hmp_trace_file(Monitor *mon, const QDict 
*qdict)
 }
 #endif
 
+#ifdef CONFIG_TRACE_RECORDER
+static void hmp_recorder(Monitor *mon, const QDict *qdict)
+{
+    const char *op = qdict_get_try_str(qdict, "op");
+    const char *arg = qdict_get_try_str(qdict, "arg");
+
+    if (!op) {
+        monitor_printf(mon, "missing recorder command\"%s\"\n", op);
+        help_cmd(mon, "recorder");
+    } else if (!strcmp(op, "trace")) {
+        recorder_trace_set(arg);
+    } else if (!strcmp(op, "dump")) {
+        if (!arg || !*arg) {
+            recorder_dump();
+        } else {
+            recorder_dump_for(arg);
+        }
+    } else {
+        monitor_printf(mon, "unexpected recorder command \"%s\"\n", op);
+        help_cmd(mon, "recorder");
+    }
+}
+#endif
+
 static void hmp_info_help(Monitor *mon, const QDict *qdict)
 {
     help_cmd(mon, "info");
diff --git a/scripts/tracetool/backend/recorder.py 
b/scripts/tracetool/backend/recorder.py
new file mode 100644
index 0000000000..79cc6f5b03
--- /dev/null
+++ b/scripts/tracetool/backend/recorder.py
@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+
+"""
+Trace back-end for recorder library
+"""
+
+__author__     = "Christophe de Dinechin <christophe@dinechin.org>"
+__copyright__  = "Copyright 2020, Christophe de Dinechin and Red Hat"
+__license__    = "GPL version 2 or (at your option) any later version"
+
+__maintainer__ = "Christophe de Dinechin"
+__email__      = "christophe@dinechin.org"
+
+
+from tracetool import out
+
+PUBLIC = True
+
+def generate_h_begin(events, group):
+    out('#include <recorder/recorder.h>', '')
+
+    for event in events:
+        out('RECORDER_DECLARE(%(name)s);', name=event.name)
+
+
+def generate_h(event, group):
+    argnames = ", ".join(event.args.names())
+    if len(event.args) > 0:
+        argnames = ", " + argnames
+
+    out('    record(%(event)s, %(fmt)s %(argnames)s);',
+        event=event.name,
+        fmt=event.fmt.rstrip("\n"),
+        argnames=argnames)
+
+
+def generate_h_backend_dstate(event, group):
+    out('    RECORDER_TWEAK(%(event_id)s) || \\', event_id=event.name)
+
+def generate_c_begin(events, group):
+    out('#include "qemu/osdep.h"',
+        '#include "trace/control.h"',
+        '#include "trace/simple.h"',
+        '#include <recorder/recorder.h>',
+        '')
+
+    for event in events:
+        out('RECORDER_DEFINE(%(name)s, 8, "Tracetool recorder for 
%(api)s(%(args)s)");',
+            name=event.name,
+            api=event.api(),
+            args=event.args)
diff --git a/trace/Makefile.objs b/trace/Makefile.objs
index c544509adf..9e347640c2 100644
--- a/trace/Makefile.objs
+++ b/trace/Makefile.objs
@@ -54,6 +54,8 @@ $(obj)/generated-tcg-tracers.h-timestamp: 
$(SRC_PATH)/trace-events $(BUILD_DIR)/
 
 util-obj-$(CONFIG_TRACE_SIMPLE) += simple.o
 util-obj-$(CONFIG_TRACE_FTRACE) += ftrace.o
+util-obj-$(CONFIG_TRACE_RECORDER) += recorder.o
+recorder.o-libs = -lrecorder
 util-obj-y += control.o
 obj-y += control-target.o
 util-obj-y += qmp.o
diff --git a/trace/control.c b/trace/control.c
index 2ffe000818..15e5293eec 100644
--- a/trace/control.c
+++ b/trace/control.c
@@ -23,6 +23,9 @@
 #ifdef CONFIG_TRACE_SYSLOG
 #include <syslog.h>
 #endif
+#ifdef CONFIG_TRACE_RECORDER
+#include "trace/recorder.h"
+#endif
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/config-file.h"
@@ -282,6 +285,10 @@ bool trace_init_backends(void)
     openlog(NULL, LOG_PID, LOG_DAEMON);
 #endif
 
+#ifdef CONFIG_TRACE_RECORDER
+    recorder_trace_init();
+#endif
+
     return true;
 }
 
diff --git a/trace/recorder.c b/trace/recorder.c
new file mode 100644
index 0000000000..cbc22ee2d5
--- /dev/null
+++ b/trace/recorder.c
@@ -0,0 +1,22 @@
+/*
+ * Recorder-based trace backend
+ *
+ * Copyright Red Hat 2020
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "trace/recorder.h"
+
+RECORDER_CONSTRUCTOR
+void recorder_trace_init(void)
+{
+    recorder_trace_set(getenv("RECORDER_TRACES"));
+
+    // Allow a dump in case we receive some unhandled signal
+    // For example, send USR2 to a hung process to get a dump
+    if (getenv("RECORDER_TRACES"))
+        recorder_dump_on_common_signals(0,0);
+}
diff --git a/trace/recorder.h b/trace/recorder.h
new file mode 100644
index 0000000000..00b11a2d2f
--- /dev/null
+++ b/trace/recorder.h
@@ -0,0 +1,34 @@
+/*
+ * Recorder-based trace backend
+ *
+ * Copyright Red Hat 2020
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef TRACE_RECORDER_H
+#define TRACE_RECORDER_H
+
+#include "qemu/osdep.h"
+
+#ifdef CONFIG_TRACE_RECORDER
+
+#include <recorder/recorder.h>
+
+extern void recorder_trace_init(void);
+
+#else
+
+// Disable recorder macros
+#define RECORDER(Name, Size, Description)
+#define RECORDER_DEFINE(Name, Size, Description)
+#define RECORDER_DECLARE(Name)
+#define RECORD(Name, ...)
+#define record(Name, ...)
+#define recorder_trace_init()
+
+#endif // CONFIG_TRACE_RECORDER
+
+#endif // TRACE_RECORDER_H
diff --git a/util/module.c b/util/module.c
index e48d9aacc0..2fa93561fe 100644
--- a/util/module.c
+++ b/util/module.c
@@ -22,6 +22,10 @@
 #ifdef CONFIG_MODULE_UPGRADES
 #include "qemu-version.h"
 #endif
+#ifdef CONFIG_TRACE_RECORDER
+#include "trace/recorder.h"
+#endif
+
 
 typedef struct ModuleEntry
 {
@@ -150,6 +154,10 @@ static int module_load_file(const char *fname)
         g_module_close(g_module);
         ret = -EINVAL;
     } else {
+#ifdef CONFIG_TRACE_RECORDER
+        // New recorders may have been pulled in, activate them if necessary
+        recorder_trace_init();
+#endif
         QTAILQ_FOREACH(e, &dso_init_list, node) {
             e->init();
             register_module_init(e->init, e->type);
-- 
2.26.2