Re: [PATCH 4/4] trace2: use system config for default trace2 settings

> 
> On Thu, Mar 28 2019, Jeff Hostetler via GitGitGadget wrote:
> 
> Thanks for working on this!
> 
> Haven't given this any deep testing. Just some observations:
> 
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Teach git to read the system config (usually "/etc/gitconfig") for
>> default Trace2 settings.  This allows system-wide Trace2 settings to
>> be installed and inherited to make it easier to manage a collection of
>> systems.

>> +/* clang-format off */
>> +static struct tr2_sysenv_entry tr2_sysenv_settings[] = {
>> +	{ "GIT_TR2_CONFIG_PARAMS",   "trace2.configparams"     },
>> +
>> +	{ "GIT_TR2_DST_DEBUG",       "trace2.destinationdebug" },
>> +
>> +	{ "GIT_TR2",                 "trace2.normaltarget"     },
>> +	{ "GIT_TR2_BRIEF",           "trace2.normalbrief"      },
>> +
>> +	{ "GIT_TR2_EVENT",           "trace2.eventtarget"      },
>> +	{ "GIT_TR2_EVENT_BRIEF",     "trace2.eventbrief"       },
>> +	{ "GIT_TR2_EVENT_NESTING",   "trace2.eventnesting"     },
>> +
>> +	{ "GIT_TR2_PERF",            "trace2.perftarget"       },
>> +	{ "GIT_TR2_PERF_BRIEF",      "trace2.perfbrief"        },
>> +};
>> +/* clang-format on */
>> +
>> +static int tr2_sysenv_cb(const char *key, const char *value, void *d)
>> +{
>> +	int k;
>> +
> 
> I added:
> 
> 	if (!starts_with(key, "trace2."))
> 		return 0;
> 
> Here, and everything works as expected. I think that's a good
> idea. Makes this O(n) over N config keys instead of O(n*x) where x = num
> entries in tr2_sysenv_settings.

> 
>> +	for (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++) {
>> +		if (!strcmp(key, tr2_sysenv_settings[k].git_config_name)) {
>> +			free(tr2_sysenv_settings[k].value);
>> +			tr2_sysenv_settings[k].value = xstrdup(value);
>> +			return 0;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * Load Trace2 settings from the system config (usually "/etc/gitconfig"
>> + * unless we were built with a runtime-prefix).  These are intended to
>> + * define the default values for Trace2 as requested by the administrator.
>> + */
>> +void tr2_sysenv_load(void)
>> +{
>> +	const char *system_config_pathname;
>> +	const char *test_pathname;
>> +
>> +	system_config_pathname = git_etc_gitconfig();
>> +
>> +	test_pathname = getenv("GIT_TEST_TR2_SYSTEM_CONFIG");
>> +	if (test_pathname) {
>> +		if (!*test_pathname || !strcmp(test_pathname, "0"))
>> +			return; /* disable use of system config */
>> +
>> +		/* mock it with given test file */
>> +		system_config_pathname = test_pathname;
>> +	}
>> +
>> +	if (file_exists(system_config_pathname))
>> +		git_config_from_file(tr2_sysenv_cb, system_config_pathname,
>> +				     NULL);
> 
> Maybe this isn't worth it, but this "file_exists" thing is something we
> could abstract in the config machinery (or maybe passing via
> "config_options" makes more sense):

>>
>> -	nesting = getenv(TR2_ENVVAR_EVENT_NESTING);
>> +	nesting = tr2_sysenv_get(TR2_SYSENV_EVENT_NESTING);
>>   	if (nesting && ((want_nesting = atoi(nesting)) > 0))
>>   		tr2env_event_nesting_wanted = want_nesting;
>>
>> -	brief = getenv(TR2_ENVVAR_EVENT_BRIEF);
>> +	brief = tr2_sysenv_get(TR2_SYSENV_EVENT_BRIEF);
>>   	if (brief && ((want_brief = atoi(brief)) > 0))
>>   		tr2env_event_brief = want_brief;
> 
> A lot of this pre-dates this patch, but I wonder if the whole of trace2
> couldn't make more use of config.c's bool parsing for things like
> these. Maybe by having a "cfg_type" enum & parsed_value void* in
> tr2_sysenv_entry?

>> -	brief = getenv(TR2_ENVVAR_NORMAL_BRIEF);
>> +	brief = tr2_sysenv_get(TR2_SYSENV_NORMAL_BRIEF);
>>   	if (brief && *brief &&
>>   	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
>>   		tr2env_normal_brief = want_brief;

>> -	brief = getenv(TR2_ENVVAR_PERF_BRIEF);
>> +	brief = tr2_sysenv_get(TR2_SYSENV_PERF_BRIEF);
>>   	if (brief && *brief &&
>>   	    ((want_brief = git_parse_maybe_bool(brief)) != -1))
>>   		tr2env_perf_brief = want_brief;