| Message ID | 20180612053548.901931-1-yhs@fb.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf,v3] tools/bpftool: fix a bug in bpftool perf | expand |
On Mon, 11 Jun 2018 22:35:48 -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 <ast@kernel.org> > Signed-off-by: Yonghong Song <yhs@fb.com> Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> FWIW :)
On 06/12/2018 07:35 AM, 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 <ast@kernel.org> > Signed-off-by: Yonghong Song <yhs@fb.com> Applied to bpf, thanks Yonghong!
diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c index ac6b1a12c9b7..b76b77dcfd1f 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); + fd = open("/", O_RDONLY); if (fd < 0) { - p_err("perf_query_support: %s", strerror(errno)); + p_err("perf_query_support: cannot open directory \"/\" (%s)", + strerror(errno)); goto out; }
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 <ast@kernel.org> Signed-off-by: Yonghong Song <yhs@fb.com> --- tools/bpf/bpftool/perf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) Changelogs: v2 -> v3: . fix a stupid error (flippingg the condition) I introduced in v2. v1 -> v2: . remove '\n' in the p_err format string in order to have valid json output.