On 03/12/19 11:07, Qais Yousef wrote: > eBPF tools like bcc-tools have hard time figuring out when features like > raw_tracepoint are supported in the kernel on which we are running. At > the moment a fragile mechanism of matching bpf_find_raw_tracepoint() > function in /proc/kallsyms is used to find out whether raw tracepoints > can be used or not. But when this function was renamed recently to > bpf_get_raw_tracepoint() the tool started to fail to use raw > tracepoints. > > To help in providing a more reliable way to detect features like > RAW_TRACEPOINT, add a new file in trace debugfs to export the supported > features. > > $cat /sys/kernel/debug/tracing/supported_features > RAW_TRACEPOINT > EXAMPLE_FEATURE_1 > EXAMPLE_FEATURE_2 > > Signed-off-by: Qais Yousef <qais.you...@arm.com> > --- > > This is a half baked patch to probe the potential of this solution. > > The breakage mentioned in the commit message is here: > > https://github.com/iovisor/bcc/pull/2241/commits/0f5849187972a50adf0d9eaa8788c11f9fd926ea > > I am not sure what else beside raw_tracepoint makes sense to expose right now. > > kernel/trace/trace.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index c4238b441624..daae09238e62 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -6670,6 +6670,28 @@ static const struct file_operations snapshot_raw_fops > = { > > #endif /* CONFIG_TRACER_SNAPSHOT */ > > +#define TRACE_FEATURE(feat)__stringify(feat) "\n" > + > +#define TRACE_FEATURES\ > +TRACE_FEATURE(RAW_TRACEPOINT)\ > +TRACE_FEATURE(EXAMPLE_FEATUTE_1)\ > +TRACE_FEATURE(EXAMPLE_FEATUTE_2) > + > +static ssize_t > +tracing_read_trace_features(struct file *filp, char __user *ubuf, > +size_t cnt, loff_t *ppos) > +{ > +char *buf = TRACE_FEATURES; > +size_t len = sizeof(TRACE_FEATURES); > + > +return simple_read_from_buffer(ubuf, cnt, ppos, buf, len); > +} > + > +static const struct file_operations show_trace_features_fops = { > +.read = tracing_read_trace_features, > +.llseek = no_llseek, > +}; > + > static int tracing_buffers_open(struct inode *inode, struct file *filp) > { > struct trace_array *tr = inode->i_private; > @@ -8242,6 +8264,9 @@ static __init int tracer_init_tracefs(void) > &ftrace_update_tot_cnt, &tracing_dyn_info_fops); > #endif > > +trace_create_file("trace_features", 0444, d_tracer, > +NULL, &show_trace_features_fops); > + > create_trace_instances(d_tracer); > > update_tracer_options(&global_trace); > -- > 2.17.1 > > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you.
Apologies that shouldn't have appeared. I can resend the patch if it matters. -- Qais Yousef
