Messages in this thread | | | Date | Tue, 30 Aug 2016 10:30:42 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCHV5 1/3] tracing: add a possibility of exporting function trace to other places instead of ring buffer only |
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On Tue, 30 Aug 2016 16:07:28 +0800 Chunyan Zhang <zhang.chunyan@linaro.org> wrote:
> Currently Function traces can be only exported to ring buffer, this > patch added trace_export concept which can process traces and export > them to a registered destination as an addition to the current only > output of Ftrace - i.e. ring buffer. > > In this way, if we want Function traces to be sent to other destination > rather than ring buffer only, we just need to register a new > trace_export and implement its own .commit() callback or just use > 'trace_generic_commit()' which this patch also added and hooks up its > own .write() function for writing traces to the storage. > > With this patch, only Function trace (trace type is TRACE_FN) > is supported. > > Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org> > --- > include/linux/trace.h | 35 ++++++++++++ > kernel/trace/trace.c | 155 +++++++++++++++++++++++++++++++++++++++++++++++++- > kernel/trace/trace.h | 1 + > 3 files changed, 190 insertions(+), 1 deletion(-) > create mode 100644 include/linux/trace.h > > diff --git a/include/linux/trace.h b/include/linux/trace.h > new file mode 100644 > index 0000000..30ded92 > --- /dev/null > +++ b/include/linux/trace.h > @@ -0,0 +1,35 @@ > +#ifndef _LINUX_TRACE_H > +#define _LINUX_TRACE_H > + > +#include <linux/ring_buffer.h> > +struct trace_array; > + > +#ifdef CONFIG_TRACING > +/* > + * The trace export - an export of Ftrace. The trace_export can process > + * traces and export them to a registered destination as an addition to > + * the current only output of Ftrace - i.e. ring buffer. > + * > + * If you want traces to be sent to some other place rather than > + * ring buffer only, just need to register a new trace_export and > + * implement its own .commit() callback or just directly use > + * 'trace_generic_commit()' and hooks up its own .write() function > + * for writing traces to the storage. > + * > + * next - pointer to the next trace_export > + * commit - commit the traces to the destination > + * write - copy traces which have been delt with ->commit() to > + * the destination > + */ > +struct trace_export { > + struct trace_export __rcu *next; > + void (*commit)(struct trace_array *, struct ring_buffer_event *); > + void (*write)(const char *, unsigned int); > +}; > + > +int register_ftrace_export(struct trace_export *export); > +int unregister_ftrace_export(struct trace_export *export); > + > +#endif /* CONFIG_TRACING */ > + > +#endif /* _LINUX_TRACE_H */ > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index dade4c9..3163fa6 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -40,6 +40,7 @@ > #include <linux/poll.h> > #include <linux/nmi.h> > #include <linux/fs.h> > +#include <linux/trace.h> > #include <linux/sched/rt.h> > > #include "trace.h" > @@ -2128,6 +2129,155 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr, > ftrace_trace_userstack(buffer, flags, pc); > } > > +static DEFINE_STATIC_KEY_FALSE(ftrace_exports_enabled); > + > +static void ftrace_exports_enable(void) > +{ > + static_branch_enable(&ftrace_exports_enabled); > +} > + > +static void ftrace_exports_disable(void) > +{ > + static_branch_disable(&ftrace_exports_enabled); > +} > + > +static size_t trace_size[] = { > + [TRACE_FN] = sizeof(struct ftrace_entry), > + [TRACE_CTX] = sizeof(struct ctx_switch_entry), > + [TRACE_WAKE] = sizeof(struct ctx_switch_entry), > + [TRACE_STACK] = sizeof(struct stack_entry), > + [TRACE_PRINT] = sizeof(struct print_entry), > + [TRACE_BPRINT] = sizeof(struct bprint_entry), > + [TRACE_MMIO_RW] = sizeof(struct trace_mmiotrace_rw), > + [TRACE_MMIO_MAP] = sizeof(struct trace_mmiotrace_map), > + [TRACE_BRANCH] = sizeof(struct trace_branch), > + [TRACE_GRAPH_RET] = sizeof(struct ftrace_graph_ret_entry), > + [TRACE_GRAPH_ENT] = sizeof(struct ftrace_graph_ent_entry), > + [TRACE_USER_STACK] = sizeof(struct userstack_entry), > + [TRACE_BPUTS] = sizeof(struct bputs_entry), > +}; > + > +static void > +trace_generic_commit(struct trace_array *tr, > + struct ring_buffer_event *event) > +{ > + struct trace_entry *entry; > + struct trace_export *export = tr->export;
Why not just pass in the export directly?
> + unsigned int size = 0; > + > + entry = ring_buffer_event_data(event); > + > + size = trace_size[entry->type];
BTW, it would make much more sense if you just did:
size = ring_buffer_event_length(event);
and get rid of that silly array, as that is prone to bugs if you add a new type.
> + if (!size) > + return; > + > + if (export && export->write) > + export->write((char *)entry, size); > +} > + > +static DEFINE_MUTEX(ftrace_export_lock); > + > +static struct trace_export __rcu *ftrace_exports_list __read_mostly; > + > +static inline void > +ftrace_exports(struct trace_array *tr, struct ring_buffer_event *event) > +{ > + struct trace_export *export; > + > + preempt_disable_notrace(); > + > + for (export = rcu_dereference_raw_notrace(ftrace_exports_list); > + export && export->commit; > + export = rcu_dereference_raw_notrace(export->next)) { > + tr->export = export; > + export->commit(tr, event);
Um, what's the commit for?
Why not just call the trace_generic_commit() above. Nothing has anything different. But change that name. Maybe call it "process_export()" or something. And pass the export directly and get rid of the tr->export.
> + } > + > + preempt_enable_notrace(); > +} > + > +static inline void > +add_trace_export(struct trace_export **list, struct trace_export *export) > +{ > + rcu_assign_pointer(export->next, *list); > + /* > + * We are entering export into the list but another > + * CPU might be walking that list. We need to make sure > + * the export->next pointer is valid before another CPU sees > + * the export pointer included into the list. > + */ > + rcu_assign_pointer(*list, export); > +} > + > +static inline int > +rm_trace_export(struct trace_export **list, struct trace_export *export) > +{ > + struct trace_export **p; > + > + for (p = list; *p != NULL; p = &(*p)->next) > + if (*p == export) > + break; > + > + if (*p != export) > + return -1; > + > + rcu_assign_pointer(*p, (*p)->next); > + > + return 0; > +} > + > +static inline void > +add_ftrace_export(struct trace_export **list, struct trace_export *export) > +{ > + if (*list == NULL) > + ftrace_exports_enable(); > + > + add_trace_export(list, export); > +} > + > +static inline int > +rm_ftrace_export(struct trace_export **list, struct trace_export *export) > +{ > + int ret; > + > + ret = rm_trace_export(list, export); > + if (*list == NULL) > + ftrace_exports_disable(); > + > + return ret; > +} > + > +int register_ftrace_export(struct trace_export *export) > +{ > + if (WARN_ON_ONCE(!export->write)) > + return -1; > + > + mutex_lock(&ftrace_export_lock); > + > + export->commit = trace_generic_commit; > + > + add_ftrace_export(&ftrace_exports_list, export); > + > + mutex_unlock(&ftrace_export_lock); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(register_ftrace_export); > + > +int unregister_ftrace_export(struct trace_export *export) > +{ > + int ret; > + > + mutex_lock(&ftrace_export_lock); > + > + ret = rm_ftrace_export(&ftrace_exports_list, export); > + > + mutex_unlock(&ftrace_export_lock); > + > + return ret; > +} > +EXPORT_SYMBOL_GPL(unregister_ftrace_export); > + > void > trace_function(struct trace_array *tr, > unsigned long ip, unsigned long parent_ip, unsigned long flags, > @@ -2146,8 +2296,11 @@ trace_function(struct trace_array *tr, > entry->ip = ip; > entry->parent_ip = parent_ip; > > - if (!call_filter_check_discard(call, entry, buffer, event)) > + if (!call_filter_check_discard(call, entry, buffer, event)) { > + if (static_branch_unlikely(&ftrace_exports_enabled)) > + ftrace_exports(tr, event); > __buffer_unlock_commit(buffer, event);
We do the generic commit here.
-- Steve
> + } > } > > #ifdef CONFIG_STACKTRACE > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index f783df4..26a3088 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -260,6 +260,7 @@ struct trace_array { > /* function tracing enabled */ > int function_enabled; > #endif > + struct trace_export *export; > }; > > enum {
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