Messages in this thread |  | | Date | Mon, 19 Feb 2018 10:21:34 +0900 | From | Namhyung Kim <> | Subject | Re: [PATCH v3] perf ftrace: Append an EOL when write tracing files |
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Hello,
On Wed, Feb 14, 2018 at 10:44:24AM +0800, changbin.du@intel.com wrote: > From: Changbin Du <changbin.du@intel.com> > > Before this change, the '--graph-funcs', '--nograph-funcs' and > '--trace-funcs' options didn't work as expected when the <func> doesn't > exist. Because the kernel side hid possible errors. > > $ sudo ./perf ftrace -a --graph-depth 1 --graph-funcs abcdefg > 0) 0.140 us | rcu_all_qs(); > 3) 0.304 us | mutex_unlock(); > 0) 0.153 us | find_vma(); > 3) 0.088 us | __fsnotify_parent(); > 0) 6.145 us | handle_mm_fault(); > 3) 0.089 us | fsnotify(); > 3) 0.161 us | __sb_end_write(); > 3) 0.710 us | SyS_close(); > 3) 7.848 us | exit_to_usermode_loop(); > > On above example, I specified function filter 'abcdefg' but all functions > are enabled. The expected error is hidden. > > The original fix is to make the kernel support '\0' as end of string: > https://lkml.org/lkml/2018/1/16/116 > > But above fix cannot be compatible with old kernels. Then Namhyung Kim > suggest adding a space after function name. > > This patch will append an '\n' when write tracing file. After this fix, > the perf will report correct error state. Also let it print an error if > reset_tracing_files() fails. > > Cc: Namhyung Kim <namhyung@kernel.org> > Signed-off-by: Changbin Du <changbin.du@intel.com> > > --- > v3: Took Kim's suggestion that add a space after function name. > v2: Rebase. > --- > tools/perf/builtin-ftrace.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c > index 25a42ac..9ffd748 100644 > --- a/tools/perf/builtin-ftrace.c > +++ b/tools/perf/builtin-ftrace.c > @@ -72,6 +72,7 @@ static int __write_tracing_file(const char *name, const char *val, bool append) > ssize_t size = strlen(val); > int flags = O_WRONLY; > char errbuf[512]; > + char *val_copy; > > file = get_tracing_file(name); > if (!file) { > @@ -91,12 +92,20 @@ static int __write_tracing_file(const char *name, const char *val, bool append) > goto out; > } > > - if (write(fd, val, size) == size) > + /* > + * Copy the original value and append a '\n'. Without this, > + * the kernel can hide possible errors. > + */ > + val_copy = strdup(val);
Please check the return value.
Thanks, Namhyung
> + val_copy[size] = '\n'; > + > + if (write(fd, val_copy, size + 1) == size + 1) > ret = 0; > else > pr_debug("write '%s' to tracing/%s failed: %s\n", > val, name, str_error_r(errno, errbuf, sizeof(errbuf))); > > + free(val_copy); > close(fd); > out: > put_tracing_file(file); > @@ -280,8 +289,10 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv) > signal(SIGCHLD, sig_handler); > signal(SIGPIPE, sig_handler); > > - if (reset_tracing_files(ftrace) < 0) > + if (reset_tracing_files(ftrace) < 0) { > + pr_err("failed to reset ftrace\n"); > goto out; > + } > > /* reset ftrace buffer */ > if (write_tracing_file("trace", "0") < 0) > -- > 2.7.4 >
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