lkml.org 
[lkml]   [2016]   [Aug]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCHV5 1/3] tracing: add a possibility of exporting function trace to other places instead of ring buffer only
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 {

\
 
 \ /
  Last update: 2016-09-17 09:58    [W:0.086 / U:3.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site