From: Changbin Du <changbin...@intel.com> The terminal character '\0' should take into account into size of the string buffer. Without this fix, the '--graph-funcs', '--nograph-funcs' and '--trace-funcs' options didn't work as expected when the <func> doesn't exist. If usersapce writes a non-terminated string, the kernel side will always return success but actually no filter applied.
As discussed before, the kernel now support '\0' to mark the end of string: https://lkml.org/lkml/2018/1/16/116 After this fix in userspace, the perf will report correct error state. Also let it print an error if reset_tracing_files() fails. The problem: $ 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. Signed-off-by: Changbin Du <changbin...@intel.com> --- tools/perf/builtin-ftrace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c index 25a42ac..a87e9b3 100644 --- a/tools/perf/builtin-ftrace.c +++ b/tools/perf/builtin-ftrace.c @@ -69,7 +69,7 @@ static int __write_tracing_file(const char *name, const char *val, bool append) { char *file; int fd, ret = -1; - ssize_t size = strlen(val); + ssize_t size = strlen(val) + 1; int flags = O_WRONLY; char errbuf[512]; @@ -280,8 +280,10 @@ 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
