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Subject[PATCH 01/44] perf trace: Associate vfs_getname()'ed pathname with fd returned from 'openat'
Date
From: Arnaldo Carvalho de Melo <acme@redhat.com>

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: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-trace.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 88561eed7950..2a85f5198da0 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -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));
--
2.14.4
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