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

[Christophe de Dinechin]

On 2020-06-30 at 11:05 CEST, Dr. David Alan Gilbert wrote...
> * Christophe de Dinechin (dinechin@redhat.com) wrote:
>> 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
>                                                           ^^^^^^^^
> is that intended?

No. I think the intent was to indicate that you could pass the name of a
recorder to dump as an arg. I'll fix.

>
>> - 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?",
>
> Having 'arg' as a filename is a bit odd; using op/arg is very generic
> for adding extra commands; but it suddenly becomes less generic if
> arg is always a filename.
>
>> +        .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
>
> I think this SRST chunk is the one that needs updating for recorder.
> (The diff has made a bit of a mess, but I think you've copy pasted the
> trace-file chunk, but forgotten to update the SRST section).

Indeed. I had forgotten to get back to the .hx file and add the documentation.

>
>> @@ -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");
>> +    }
>> +}
>
> Consider whether just doing two separate commands would be easier;
> a recorder-trace and recorder-dump for example; that's fine from a HMP
> point of view and I think you'll find it's less code.

Hmmm. Looking back at the code, I see that I should also probably name the
commands something beginning with trace. Maybe trace-record and trace-dump?


>
> Dave
>
>> +#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
>>


--
Cheers,
Christophe de Dinechin (IRC c3d)