Re: [RFC PATCH 2/5] tracing/events: nicer print format for parsing

[Steven Rostedt]

On Wed, 10 Jun 2009, Ingo Molnar wrote:
> 
> And i kind of like the whole notion on a design level as weell: the 
> kernel exporting C source code for tools :-)
> 
> 	Ingo
> 
> ------------------>
> 
> struct record {
> 	unsigned short common_type;
> 	unsigned char common_flags;
> 	unsigned char common_preempt;
> 	int common_pid;
> 	int common_tgid;
> 	int dev;
> 	unsigned long long sector;
> 	unsigned int nr_sector;
> 	char rwbs[6];
> 	char comm[16];
> } this_record = { 1, 2, 3, 4, 5, 6, 7, 8, { 'a', }, "abc" };
> 
> void main(void)
> {
> 	struct record *REC = &this_record;
> 
> 	printf("%d,%d %s %llu + %u [%s]", ((unsigned int) ((REC->dev) >> 20)), ((unsigned int) ((REC->dev) & ((1U << 20) - 1))), REC->rwbs, (unsigned long long)REC->sector, REC->nr_sector, REC->comm);
> }

I actually tried this first. But it breaks once we start getting types 
into the code:

print fmt: "call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s",
          REC->call_site, REC->ptr, REC->bytes_req, REC->bytes_alloc, 
          (REC->gfp_flags) ? ({ static const struct trace_print_flags 
          flags[] = { {(unsigned long)(((gfp_t)0x10u) | ((gfp_t)0x40u) |
                      ((gfp_t)0x80u) | ((gfp_t)0x20000u) | ((gfp_t)0x02u) | 
                       ((gfp_t)0x100000u)), "GFP_HIGHUSER_MOVABLE"}, [...]

Will break on gfp_t. We also have cases where the enum name slips in too:

print fmt: "softirq=%d action=%s", REC->vec, ({ static const struct trace_print_flags symbols[] =
            { { HI_SOFTIRQ, "HI" }, { TIMER_SOFTIRQ, "TIMER" }, { NET_TX_SOFTIRQ, "NET_TX" },
              { NET_RX_SOFTIRQ, "NET_RX" }, { BLOCK_SOFTIRQ, "BLOCK" },
              { TASKLET_SOFTIRQ, "TASKLET" }, { SCHED_SOFTIRQ, "SCHED" },
              { HRTIMER_SOFTIRQ, "HRTIMER" }, { RCU_SOFTIRQ, "RCU" },
              { -1, ((void *)0) }}; ftrace_print_symbols_seq(p, REC->vec, symbols); })

Yes we can add special types for things like gfp_t, but as we get more and 
more users of TRACE_EVENT, the tools will never be able to keep up.

-- Steve

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/