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    SubjectRe: [RFC][PATCH 1/2] tracing/ftrace: syscall tracing infrastructure

    On Sat, 7 Mar 2009, Frederic Weisbecker wrote:
    > +
    > +
    > +static atomic_t refcount;
    > +
    > +enum print_line_t
    > +print_syscall_enter(struct trace_iterator *iter, int flags)
    > +{
    > + struct trace_seq *s = &iter->seq;
    > + struct trace_entry *ent = iter->ent;
    > + struct syscall_trace_enter *trace;
    > + enum syscall_trace_nr syscall;
    > + const struct syscall_trace_entry *entry;
    > + char *str = NULL;
    > + int i, ret;
    > +
    > + trace_assign_type(trace, ent);
    > +
    > + syscall = trace->nr;
    > +
    > + if (!syscall || syscall >= __SYSCALL_TRACE_END)

    You still need to print a "\n" otherwise the output of the next line
    will start on the current line.

    > + return TRACE_TYPE_HANDLED;
    > +
    > + entry = &syscall_trace_entries[syscall];
    > + if (!entry->simple_format) {
    > + ret = entry->output.print(trace->args);
    > + if (!ret)
    > + return TRACE_TYPE_PARTIAL_LINE;
    > + return TRACE_TYPE_HANDLED;
    > + }
    > +
    > + ret = trace_seq_printf(s, "syscall %s :", entry->name);
    > + if (!ret)
    > + return TRACE_TYPE_PARTIAL_LINE;
    > +
    > + for (i = 0; i < entry->nb_args; i++) {
    > + /*
    > + * FIXME: the string comes from the user, but on tracing
    > + * output time, it may have disappeared from the memory.
    > + * May be better to strdup it on tracing time.
    > + */
    > + if (entry->output.string_mask & (1 << i)) {
    > + /* 128 is enough for most path */
    > + str = strndup_user((char *)trace->args[i], 128);
    > +
    > + /* If it faulted badly, the error shoud have been
    > + * handled while servicing the syscall, just ignore.
    > + */
    > + if (str == ERR_PTR(-EFAULT) || str == ERR_PTR(-EINVAL)
    > + || str == ERR_PTR(-ENOMEM))
    > + return TRACE_TYPE_HANDLED;
    > +
    > + ret = trace_seq_printf(s, " %s", str);
    > + } else {
    > + ret = trace_seq_printf(s, " 0x%lx", trace->args[i]);
    > + }
    > + if (!ret)
    > + goto end_partial;
    > + }
    > + if (!trace_seq_printf(s, "\n"))
    > + goto end_partial;
    > +
    > + kfree(str);
    > + return TRACE_TYPE_HANDLED;
    > +
    > +end_partial:
    > + kfree(str);
    > + return TRACE_TYPE_PARTIAL_LINE;
    > +}
    > +
    > +enum print_line_t
    > +print_syscall_exit(struct trace_iterator *iter, int flags)
    > +{
    > + struct trace_seq *s = &iter->seq;
    > + struct trace_entry *ent = iter->ent;
    > + struct syscall_trace_exit *trace;
    > + enum syscall_trace_nr syscall;
    > + const struct syscall_trace_entry *entry;
    > + int ret;
    > +
    > + trace_assign_type(trace, ent);
    > +
    > + syscall = trace->nr;
    > +
    > + if (!syscall || syscall >= __SYSCALL_TRACE_END)
    > + return TRACE_TYPE_HANDLED;
    > +
    > + entry = &syscall_trace_entries[syscall];
    > +
    > + ret = trace_seq_printf(s, "syscall %s -> 0x%lx\n", entry->name,
    > + trace->ret);
    > + if (!ret)
    > + return TRACE_TYPE_PARTIAL_LINE;
    > +
    > + return TRACE_TYPE_HANDLED;
    > +}
    > +
    > +void start_ftrace_syscalls(void)
    > +{
    > + unsigned long flags;
    > + struct task_struct *g, *t;
    > +
    > + if (atomic_inc_return(&refcount) != 1)
    > + goto out;
    > +
    > + read_lock_irqsave(&tasklist_lock, flags);
    > +
    > + do_each_thread(g, t) {
    > + set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
    > + } while_each_thread(g, t);
    > +
    > + read_unlock_irqrestore(&tasklist_lock, flags);
    > +
    > + return;
    > +out:
    > + atomic_dec(&refcount);
    > +}
    > +
    > +void stop_ftrace_syscalls(void)
    > +{
    > + unsigned long flags;
    > + struct task_struct *g, *t;
    > +
    > + if (atomic_dec_return(&refcount))
    > + return;
    > +
    > + read_lock_irqsave(&tasklist_lock, flags);
    > +
    > + do_each_thread(g, t) {
    > + clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
    > + } while_each_thread(g, t);
    > +
    > + read_unlock_irqrestore(&tasklist_lock, flags);
    > +}
    > +
    > +void ftrace_syscall_enter(struct pt_regs *regs)
    > +{
    > + struct trace_array *tr = __get_global_trace();
    > + struct syscall_trace_enter *entry;
    > + const struct syscall_trace_entry *sys_data;
    > + struct ring_buffer_event *event;
    > + struct trace_array_cpu *data;
    > + int size;
    > + int syscall_nr;
    > + int nr_offset;
    > + int cpu;
    > +
    > + syscall_nr = syscall_get_nr(current, regs);
    > + nr_offset = arch_syscall_trace_nr[syscall_nr];
    > + if (!nr_offset || nr_offset >= __SYSCALL_TRACE_END)
    > + return;
    > +
    > + cpu = raw_smp_processor_id();
    > + data = tr->data[cpu];
    > +
    > + if (unlikely(atomic_read(&data->disabled)))
    > + return;
    > +
    > + sys_data = &syscall_trace_entries[nr_offset];
    > + size = sizeof(*entry) + sizeof(unsigned long) * sys_data->nb_args;
    > +
    > + event = trace_buffer_lock_reserve(tr, TRACE_SYSCALL_ENTER, size, 0, 0);
    > + if (!event)
    > + return;
    > +
    > + entry = ring_buffer_event_data(event);
    > + entry->nr = nr_offset;
    > + syscall_get_arguments(current, regs, 0, sys_data->nb_args, entry->args);
    > +
    > + ring_buffer_unlock_commit(tr->buffer, event);

    BTW, you should always use the matching lock. Above you used
    trace_buffer_lock_reserve, and here you use ring_buffer_unlock_commit.
    This may not work in the future. There is a trace_buffer_unlock_commit
    too.

    But you are going to change these to trace_current_buffer_lock_reserve and
    trace_current_buffer_unlock_commit anyway ;-)


    > + trace_wake_up();
    > +}
    > +
    > +void ftrace_syscall_exit(struct pt_regs *regs)
    > +{
    > + struct trace_array *tr = __get_global_trace();
    > + struct syscall_trace_exit *entry;
    > + const struct syscall_trace_entry *sys_data;
    > + struct ring_buffer_event *event;
    > + struct trace_array_cpu *data;
    > + int syscall_nr;
    > + int nr_offset;
    > + int cpu;
    > +
    > + syscall_nr = syscall_get_nr(current, regs);
    > + nr_offset = arch_syscall_trace_nr[syscall_nr];
    > + if (!nr_offset || nr_offset >= __SYSCALL_TRACE_END)
    > + return;
    > +
    > + cpu = raw_smp_processor_id();
    > + data = tr->data[cpu];
    > +
    > + if (unlikely(atomic_read(&data->disabled)))
    > + return;
    > +
    > + sys_data = &syscall_trace_entries[nr_offset];
    > +
    > + event = trace_buffer_lock_reserve(tr, TRACE_SYSCALL_EXIT,
    > + sizeof(*entry), 0, 0);
    > + if (!event)
    > + return;
    > +
    > + entry = ring_buffer_event_data(event);
    > + entry->nr = nr_offset;
    > + entry->ret = syscall_get_return_value(current, regs);
    > +
    > + ring_buffer_unlock_commit(tr->buffer, event);

    Same here.

    -- Steve

    > + trace_wake_up();
    > +}
    > +
    > +static int init_syscall_tracer(struct trace_array *tr)
    > +{
    > + start_ftrace_syscalls();
    > +
    > + return 0;
    > +}
    > +
    > +static void reset_syscall_tracer(struct trace_array *tr)
    > +{
    > + stop_ftrace_syscalls();
    > +}
    > +
    > +static struct trace_event syscall_enter_event = {
    > + .type = TRACE_SYSCALL_ENTER,
    > + .trace = print_syscall_enter,
    > +};
    > +
    > +static struct trace_event syscall_exit_event = {
    > + .type = TRACE_SYSCALL_EXIT,
    > + .trace = print_syscall_exit,
    > +};
    > +
    > +static struct tracer syscall_tracer __read_mostly = {
    > + .name = "syscall",
    > + .init = init_syscall_tracer,
    > + .reset = reset_syscall_tracer
    > +};
    > +
    > +__init int register_ftrace_syscalls(void)
    > +{
    > + int ret;
    > +
    > + ret = register_ftrace_event(&syscall_enter_event);
    > + if (!ret) {
    > + printk(KERN_WARNING "event %d failed to register\n",
    > + syscall_enter_event.type);
    > + WARN_ON_ONCE(1);
    > + }
    > +
    > + ret = register_ftrace_event(&syscall_exit_event);
    > + if (!ret) {
    > + printk(KERN_WARNING "event %d failed to register\n",
    > + syscall_exit_event.type);
    > + WARN_ON_ONCE(1);
    > + }
    > +
    > + return register_tracer(&syscall_tracer);
    > +}
    > +device_initcall(register_ftrace_syscalls);
    > --
    > 1.6.1
    >
    >
    >


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      Last update: 2009-03-09 14:55    [W:4.033 / U:21.560 seconds]
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