linux-kernel - Re: [PATCH 07/10] perf record: Support synthesizing cgroup events

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Message-ID: <20200306141528.GD290743@krava>
Date:   Fri, 6 Mar 2020 15:15:28 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 07/10] perf record: Support synthesizing cgroup events

On Fri, Mar 06, 2020 at 03:14:09PM +0100, Jiri Olsa wrote:
> On Mon, Feb 24, 2020 at 01:37:46PM +0900, Namhyung Kim wrote:
> 
> SNIP
> 
> > +	d = opendir(path);
> > +	if (d == NULL) {
> > +		pr_debug("failed to open directory: %s\n", path);
> > +		return -1;
> > +	}
> > +
> > +	while ((dent = readdir(d)) != NULL) {
> > +		if (dent->d_type != DT_DIR)
> > +			continue;
> > +		if (!strcmp(dent->d_name, ".") ||
> > +		    !strcmp(dent->d_name, ".."))
> > +			continue;
> > +
> > +		/* any sane path should be less than PATH_MAX */
> > +		if (strlen(path) + strlen(dent->d_name) + 1 >= PATH_MAX)
> > +			continue;
> > +
> > +		if (path[pos - 1] != '/')
> > +			strcat(path, "/");
> > +		strcat(path, dent->d_name);
> > +
> > +		ret = perf_event__walk_cgroup_tree(tool, event, path,
> > +						   mount_len, process, machine);
> > +		if (ret < 0)
> > +			break;
> > +
> > +		path[pos] = '\0';
> > +	}
> > +
> > +	closedir(d);
> > +	return ret;
> > +}
> > +
> > +int perf_event__synthesize_cgroups(struct perf_tool *tool,
> > +				   perf_event__handler_t process,
> > +				   struct machine *machine)
> > +{
> > +	union perf_event event;
> > +	char cgrp_root[PATH_MAX];
> > +	size_t mount_len;  /* length of mount point in the path */
> > +
> > +	if (cgroupfs__mountpoint(cgrp_root, PATH_MAX, "perf_event") < 0) {
> > +		pr_debug("cannot find cgroup mount point\n");
> > +		return -1;
> > +	}
> > +
> > +	mount_len = strlen(cgrp_root);
> > +	/* make sure the path starts with a slash (after mount point) */
> > +	strcat(cgrp_root, "/");
> 
> the code above checks on this and seems to add '/' if needed,
> is this strcat necessary?

nah nevermind.. it's the recursive call check above, ok

jirka