perf symbols: Allow forcing reading of non-root owned files by root

When the root user tries to read a file owned by some other user we get:

# ls -la perf.data
-rw-------. 1 acme acme 20032 Nov 12 15:50 perf.data
# perf report
File perf.data not owned by current user or root (use -f to override)
# perf report -f | grep -v ^# | head -2
30.96% ls [kernel.vmlinux] [k] do_set_pte
28.24% ls libc-2.20.so [.] intel_check_word
#

That wasn't happening when the symbol code tried to read a JIT map,
where the same check was done but no forcing was possible, fix it.

Reported-by: Brendan Gregg <[e-mail]>
Tested-by: Brendan Gregg <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://permalink.gmane.org/gmane.linux.kernel.perf.user/2380
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-report.c

···
 struct report {
 	struct perf_tool	tool;
 	struct perf_session	*session;
-	bool			force, use_tui, use_gtk, use_stdio;
+	bool			use_tui, use_gtk, use_stdio;
 	bool			hide_unresolved;
 	bool			dont_use_callchains;
 	bool			show_full_info;
···
 		   "file", "vmlinux pathname"),
 	OPT_STRING(0, "kallsyms", &symbol_conf.kallsyms_name,
 		   "file", "kallsyms pathname"),
-	OPT_BOOLEAN('f', "force", &report.force, "don't complain, do it"),
+	OPT_BOOLEAN('f', "force", &symbol_conf.force, "don't complain, do it"),
 	OPT_BOOLEAN('m', "modules", &symbol_conf.use_modules,
 		    "load module symbols - WARNING: use only with -k and LIVE kernel"),
 	OPT_BOOLEAN('n', "show-nr-samples", &symbol_conf.show_nr_samples,
···
 	}
 
 	file.path  = input_name;
-	file.force = report.force;
+	file.force = symbol_conf.force;
 
 repeat:
 	session = perf_session__new(&file, false, &report.tool);

tools/perf/util/symbol.c

···
 		if (lstat(dso->name, &st) < 0)
 			goto out;
 
-		if (st.st_uid && (st.st_uid != geteuid())) {
+		if (!symbol_conf.force && st.st_uid && (st.st_uid != geteuid())) {
 			pr_warning("File %s not owned by current user or root, "
-				"ignoring it.\n", dso->name);
+				   "ignoring it (use -f to override).\n", dso->name);
 			goto out;
 		}
 

tools/perf/util/symbol.h

···
 	unsigned short	priv_size;
 	unsigned short	nr_events;
 	bool		try_vmlinux_path,
+			force,
 			ignore_vmlinux,
 			ignore_vmlinux_buildid,
 			show_kernel_path,