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Commit 6a648b53 authored by Arnaldo Carvalho de Melo's avatar Arnaldo Carvalho de Melo
Browse files

perf trace: Associate vfs_getname()'ed pathname with fd returned from 'openat' 

When the vfs_getname() wannabe tracepoint is in place:

  # perf probe -l
    probe:vfs_getname    (on getname_flags:73@acme/git/linux/fs/namei.c with pathname)
  #

'perf trace' will use it to get the pathname when it is copied from
userspace to the kernel, right after syscalls:sys_enter_open, copied
in the 'probe:vfs_getname', stash it somewhere and then, at
syscalls:sys_exit_open time, if the 'open' return is not -1, i.e. a
successfull open syscall, associate that pathname to this return, i.e.
the fd.

We were not doing this for the 'openat' syscall, which would cause 'perf
trace' to fallback to using /proc to get the fd, change it so that we
use what we got from probe:vfs_getname, reducing the 'openat'
beautification process cost, ditching the syscalls performed to read
procfs state and avoiding some possible races in the process.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-xnp44ao3bkb6ejeczxfnjwsh@git.kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent ec2cb7a5

tools/perf/builtin-trace.c

+8 −5
Original line number Diff line number Diff line
@@ -121,7 +121,6 @@ struct trace { 
	bool			force;

	bool			vfs_getname;

	int			trace_pgfaults;

	int			open_id;

};



struct tp_field {
@@ -805,12 +804,17 @@ static struct syscall_fmt *syscall_fmt__find(const char *name) 
	return bsearch(name, syscall_fmts, nmemb, sizeof(struct syscall_fmt), syscall_fmt__cmp);

}



/*

 * is_exit: is this "exit" or "exit_group"?

 * is_open: is this "open" or "openat"? To associate the fd returned in sys_exit with the pathname in sys_enter.

 */

struct syscall {

	struct event_format *tp_format;

	int		    nr_args;

	bool		    is_exit;

	bool		    is_open;

	struct format_field *args;

	const char	    *name;

	bool		    is_exit;

	struct syscall_fmt  *fmt;

	struct syscall_arg_fmt *arg_fmt;

};
@@ -1299,6 +1303,7 @@ static int trace__read_syscall_info(struct trace *trace, int id) 
	}



	sc->is_exit = !strcmp(name, "exit_group") || !strcmp(name, "exit");

	sc->is_open = !strcmp(name, "open") || !strcmp(name, "openat");



	return syscall__set_arg_fmts(sc);

}
@@ -1722,7 +1727,7 @@ static int trace__sys_exit(struct trace *trace, struct perf_evsel *evsel, 


	ret = perf_evsel__sc_tp_uint(evsel, ret, sample);



	if (id == trace->open_id && ret >= 0 && ttrace->filename.pending_open) {

	if (sc->is_open && ret >= 0 && ttrace->filename.pending_open) {

		trace__set_fd_pathname(thread, ret, ttrace->filename.name);

		ttrace->filename.pending_open = false;

		++trace->stats.vfs_getname;
@@ -3205,8 +3210,6 @@ int cmd_trace(int argc, const char **argv) 
		}

	}



	trace.open_id = syscalltbl__id(trace.sctbl, "open");



	err = target__validate(&trace.opts.target);

	if (err) {

		target__strerror(&trace.opts.target, err, bf, sizeof(bf));