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SubjectRe: [PATCH 1/4] tracing: add run-time field descriptions for event filtering
Hi Tom,


On Sun, Mar 22, 2009 at 03:30:39AM -0500, Tom Zanussi wrote:
> This patch makes the field descriptions defined for event tracing
> available at run-time, for the event-filtering mechanism introduced in a
> subsequent patch.
>
> The common event fields are prepended with 'common_' in the format
> display, allowing them to be distinguished from the other fields that
> might internally have same name and can therefore be unambiguously used
> in filters.
>
> Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
>
> ---
> kernel/trace/trace.h | 30 ++++++++++++++++-------
> kernel/trace/trace_events.c | 40 ++++++++++++++++++++++++++++++-
> kernel/trace/trace_events_stage_2.h | 45 +++++++++++++++++++++++++++++++++++
> kernel/trace/trace_events_stage_3.h | 2 +
> 4 files changed, 107 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 7cfb741..9288dc7 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -775,16 +775,26 @@ enum {
> TRACE_EVENT_TYPE_RAW = 2,
> };
>
> +struct ftrace_event_field {
> + struct list_head link;
> + char *name;
> + char *type;
> + int offset;
> + int size;
> +};
> +
> struct ftrace_event_call {
> - char *name;
> - char *system;
> - struct dentry *dir;
> - int enabled;
> - int (*regfunc)(void);
> - void (*unregfunc)(void);
> - int id;
> - int (*raw_init)(void);
> - int (*show_format)(struct trace_seq *s);
> + char *name;
> + char *system;
> + struct dentry *dir;
> + int enabled;
> + int (*regfunc)(void);
> + void (*unregfunc)(void);
> + int id;
> + int (*raw_init)(void);
> + int (*show_format)(struct trace_seq *s);
> + int (*define_fields)(void);
> + struct list_head fields;
>
> #ifdef CONFIG_EVENT_PROFILE
> atomic_t profile_count;
> @@ -793,6 +803,8 @@ struct ftrace_event_call {
> #endif
> };
>
> +int trace_define_field(struct ftrace_event_call *call, char *type,
> + char *name, int offset, int size);
> void event_trace_printk(unsigned long ip, const char *fmt, ...);
> extern struct ftrace_event_call __start_ftrace_events[];
> extern struct ftrace_event_call __stop_ftrace_events[];
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 3047b56..961b057 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -19,6 +19,34 @@
>
> static DEFINE_MUTEX(event_mutex);
>
> +int trace_define_field(struct ftrace_event_call *call, char *type,
> + char *name, int offset, int size)
> +{
> + struct ftrace_event_field *field;
> +
> + field = kmalloc(sizeof(*field), GFP_KERNEL);
> + if (!field)
> + goto err;
> + field->name = kstrdup(name, GFP_KERNEL);
> + if (!field->name)
> + goto err;
> + field->type = kstrdup(type, GFP_KERNEL);
> + if (!field->type)
> + goto err;
> + field->offset = offset;
> + field->size = size;
> + list_add(&field->link, &call->fields);
> +
> + return 0;
> +err:
> + if (field) {
> + kfree(field->name);
> + kfree(field->type);


You need kzalloc to allocate field.
With kmalloc, field will point to random filled memory
after a fresh allocation.

Imagine this path:

if (!field->name)
goto err;
...
err:
kfree(field->name) <- field->name = NULL, correct
kfree(field->type) <- field->type = ?

> + }
> + kfree(field);
> + return -ENOMEM;
> +}
> +
> static void ftrace_clear_events(void)
> {
> struct ftrace_event_call *call = (void *)__start_ftrace_events;
> @@ -343,7 +371,8 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
>
> #undef FIELD
> #define FIELD(type, name) \
> - #type, #name, offsetof(typeof(field), name), sizeof(field.name)
> + #type, "common_" #name, offsetof(typeof(field), name), \
> + sizeof(field.name)
>
> static int trace_write_header(struct trace_seq *s)
> {
> @@ -581,6 +610,15 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
> call->name);
> }
>
> + if (call->define_fields) {
> + ret = call->define_fields();
> + if (ret < 0) {
> + pr_warning("Could not initialize trace point"
> + " events/%s\n", call->name);
> + return ret;
> + }
> + }
> +
> /* A trace may not want to export its format */
> if (!call->show_format)
> return 0;
> diff --git a/kernel/trace/trace_events_stage_2.h b/kernel/trace/trace_events_stage_2.h
> index 5117c43..30743f7 100644
> --- a/kernel/trace/trace_events_stage_2.h
> +++ b/kernel/trace/trace_events_stage_2.h
> @@ -129,3 +129,48 @@ ftrace_format_##call(struct trace_seq *s) \
> }
>
> #include <trace/trace_event_types.h>
> +
> +#undef __field
> +#define __field(type, item) \
> + ret = trace_define_field(event_call, #type, #item, \
> + offsetof(typeof(field), item), \
> + sizeof(field.item)); \
> + if (ret) \
> + return ret;
> +
> +#undef __array
> +#define __array(type, item, len) \
> + ret = trace_define_field(event_call, #type "[" #len "]", #item, \
> + offsetof(typeof(field), item), \
> + sizeof(field.item)); \
> + if (ret) \
> + return ret;
> +
> +#define __common_field(type, item) \
> + ret = trace_define_field(event_call, #type, "common_" #item, \
> + offsetof(typeof(field.ent), item), \
> + sizeof(field.ent.item)); \
> + if (ret) \
> + return ret;
> +
> +#undef TRACE_EVENT
> +#define TRACE_EVENT(call, proto, args, tstruct, func, print) \
> +int \
> +ftrace_define_fields_##call(void) \
> +{ \
> + struct ftrace_raw_##call field; \
> + struct ftrace_event_call *event_call = &event_##call; \
> + int ret; \
> + \
> + __common_field(unsigned char, type); \
> + __common_field(unsigned char, flags); \
> + __common_field(unsigned char, preempt_count); \
> + __common_field(int, pid); \
> + __common_field(int, tgid); \
> + \
> + tstruct; \
> + \
> + return ret; \
> +}
> +
> +#include <trace/trace_event_types.h>
> diff --git a/kernel/trace/trace_events_stage_3.h b/kernel/trace/trace_events_stage_3.h
> index 6b3261c..468938f 100644
> --- a/kernel/trace/trace_events_stage_3.h
> +++ b/kernel/trace/trace_events_stage_3.h
> @@ -252,6 +252,7 @@ static int ftrace_raw_init_event_##call(void) \
> if (!id) \
> return -ENODEV; \
> event_##call.id = id; \
> + INIT_LIST_HEAD(&event_##call.fields); \
> return 0; \
> } \
> \
> @@ -264,6 +265,7 @@ __attribute__((section("_ftrace_events"))) event_##call = { \
> .regfunc = ftrace_raw_reg_event_##call, \
> .unregfunc = ftrace_raw_unreg_event_##call, \
> .show_format = ftrace_format_##call, \
> + .define_fields = ftrace_define_fields_##call, \
> _TRACE_PROFILE_INIT(call) \
> }
>

Other than the small possible memory leak, it looks good.

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>



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