[DTrace-devel] [PATCH] Implement the ppid builtin D variable

[Eugene Loh]

The other reply slipped out before I wrote anything.  Sorry. Let's try 
this again...


On 09/16/2020 02:02 PM, Kris Van Hees wrote:
> On Wed, Sep 16, 2020 at 02:16:33PM -0400, eugene.loh at oracle.com wrote:
>> diff --git a/bpf/get_bvar.c b/bpf/get_bvar.c
>> @@ -46,6 +46,17 @@ noinline uint64_t dt_get_bvar(dt_mstate_t *mst, uint32_t id)
>>   
>>   		return val & 0x00000000ffffffffUL;
>>   	}
>> +	case DIF_VAR_PPID: {
>> +		uint64_t	ptr = bpf_get_current_task();
>> +		int32_t		val = -1;
>> +
>> +		if (ptr == 0)
>> +			return -1;
>> +
>> +		bpf_probe_read((void *) &ptr, 8, (const void *) (ptr + mst->offparent));
>> +		bpf_probe_read((void *) &val, 4, (const void *) (ptr + mst->offtgid));
> I suggested storing the offsets in the 'state' map rather than the 'mem' map.

Right, sorry.  But what is the 'state' map?

     $ grep create_gmap libdtrace/dt_bpf.c
     create_gmap(dtrace_hdl_t *dtp, const char *name, enum bpf_map_type 
type,
         if (create_gmap(dtp, "buffers", BPF_MAP_TYPE_PERF_EVENT_ARRAY,
         ci_mapfd = create_gmap(dtp, "cpuinfo", BPF_MAP_TYPE_PERCPU_ARRAY,
         ci_memfd = create_gmap(dtp, "mem", BPF_MAP_TYPE_PERCPU_ARRAY,
         if (create_gmap(dtp, "strtab", BPF_MAP_TYPE_ARRAY,
             create_gmap(dtp, "gvars", BPF_MAP_TYPE_ARRAY,
             create_gmap(dtp, "tvars", BPF_MAP_TYPE_ARRAY,

'mstate' was the closest I found, and it's in mem.