From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yonghong Song Subject: Re: [PATCH bpf] tools/bpftool: fix a bug in bpftool perf Date: Mon, 11 Jun 2018 18:51:59 -0700 Message-ID: <6a2b9ae2-d9bb-d5de-9700-0ec5846fb1ca@fb.com> References: <20180612011516.4171096-1-yhs@fb.com> <20180611184902.23c13235@cakuba.netronome.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , To: Jakub Kicinski Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:45080 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934105AbeFLBwi (ORCPT ); Mon, 11 Jun 2018 21:52:38 -0400 In-Reply-To: <20180611184902.23c13235@cakuba.netronome.com> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 6/11/18 6:49 PM, Jakub Kicinski wrote: > On Mon, 11 Jun 2018 18:15:16 -0700, Yonghong Song wrote: >> Commit b04df400c302 ("tools/bpftool: add perf subcommand") >> introduced bpftool subcommand perf to query bpf program >> kuprobe and tracepoint attachments. >> >> The perf subcommand will first test whether bpf subcommand >> BPF_TASK_FD_QUERY is supported in kernel or not. It does it >> by opening a file with argv[0] and feeds the file descriptor >> and current task pid to the kernel for querying. >> >> Such an approach won't work if the argv[0] cannot be opened >> successfully in the current directory. This is especially >> true when bpftool is accessible through PATH env variable. >> The error below reflects the open failure for file argv[0] >> at home directory. >> >> [yhs@localhost ~]$ which bpftool >> /usr/local/sbin/bpftool >> [yhs@localhost ~]$ bpftool perf >> Error: perf_query_support: No such file or directory >> >> To fix the issue, let us open root directory ("/") >> which exists in every linux system. With the fix, the >> error message will correctly reflect the permission issue. >> >> [yhs@localhost ~]$ which bpftool >> /usr/local/sbin/bpftool >> [yhs@localhost ~]$ bpftool perf >> Error: perf_query_support: Operation not permitted >> HINT: non root or kernel doesn't support TASK_FD_QUERY >> >> Fixes: b04df400c302 ("tools/bpftool: add perf subcommand") >> Reported-by: Alexei Starovoitov >> Signed-off-by: Yonghong Song >> --- >> tools/bpf/bpftool/perf.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c >> index ac6b1a12c9b7..f1e4c9b270e2 100644 >> --- a/tools/bpf/bpftool/perf.c >> +++ b/tools/bpf/bpftool/perf.c >> @@ -29,9 +29,10 @@ static bool has_perf_query_support(void) >> if (perf_query_supported) >> goto out; >> >> - fd = open(bin_name, O_RDONLY); >> - if (fd < 0) { >> - p_err("perf_query_support: %s", strerror(errno)); >> + fd = open("/", O_RDONLY); >> + if (fd > 0) { >> + p_err("perf_query_support: cannot open directory \"/\" (%s)\n", > > nit: no \n at the end of p_err() format, because it breaks JSON :( Thanks for letting me know. Will send v2 to fix this! > >> + strerror(errno)); >> goto out; >> } >> >