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From: "Denis V. Lunev" <den@openvz.org>
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Date: Mon, 12 Oct 2015 16:58:20 +0300
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Subject: Re: [Qemu-devel] [PATCH 1/1] log hmp/qmp command
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To: Eric Blake <eblake@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, qemu-devel@nongnu.org, Pavel Butsykin <pbutsykin@virtuozzo.com>

On 10/12/2015 04:49 PM, Eric Blake wrote:
> On 10/12/2015 02:41 AM, Denis V. Lunev wrote:
>> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
>>
>> This log would be very welcome for long-term diagnostics of the system
>> in the production. This log is at least necessary to understand what
>> has been happened on the system and to identify issues at higher-level
>> subsystems (libvirt, etc).
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Markus Armbruster <armbru@redhat.com>
>> CC: Luiz Capitulino <lcapitulino@redhat.com>
>> CC: Eric Blake <eblake@redhat.com>
>> ---
>> @@ -3822,6 +3824,8 @@ static void handle_qmp_command(JSONMessageParser *parser, QList *tokens)
>>           error_setg(&local_err, QERR_JSON_PARSING);
>>           goto err_out;
>>       }
>> +    qemu_log_mask(LOG_CMD, "qmp \"%s\" requested\n",
>> +                  qobject_to_json(obj)->string);
>>   
> In addition to the leak already pointed out, qobject_to_json() can be
> expensive, and it looks like we are doing that work unconditionally even
> if the logging is not turned on. Is there a way to optimize so that the
> conversion is only done when logging is enabled?
>
this seems quite reasonable.

Will it be good if we'll change logging implementation to
use macros, something like

#define qemu_log_mask(int mask, const char *ftp, ...) \
do { \
va_list ap; \
   \
if (!(qemu_loglevel & mask) || !qemu_logfile) {\
       break;\
   }\
   qemu_log(ftp, __VA_ARGS__); \
} while (0)

This IMHO makes sense even out of the scope of this patch.

Den