Re: [PATCHv2 perf/core 2/2] tools lib bpf: Sync with samples/bpf/libbpf

From: Wangnan (F)
Date: Wed Nov 16 2016 - 22:21:32 EST




On 2016/11/17 10:46, Joe Stringer wrote:
On 16 November 2016 at 18:10, Wangnan (F) <wangnan0@xxxxxxxxxx> wrote:
I'm also working on improving bpf.c. Please have a look at:

https://lkml.org/lkml/2016/11/14/1078

Since bpf.c is simple, I think we can add more functions and fixes
gradually, instead of a full copy.

See my inline comment below.
Ah, I missed this, my apologies. It looks like it will provide much of
what I need, I can reassess this patch with your series in mind.

One comment though for your patch (I don't have the original thread to
respond to unfortunately): The map_pin and map_get functions in your
patch series can be used to pin progs too, so maybe there is a better
name? You'll see that this patch uses bpf_obj_{pin,get}() - although I
wouldn't want those to be confused with the libbpf.c objects so maybe
there's a clearer name that could be used.

The full thread can be found:

https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1272045.html

(lkml.kernel.org is not working for me, sorry)

In that patch set, bpf_map_pin/get is linked into perf hooks, so BPF script
can pin a map to sysfs. I think this feature would be useful, but I don't
have an example to show how to use it. I didn't provide program pinning/get
interface because in perf hook they are not useful. After rethinking your
suggestion now I think it is okay to provide bpf_obj_{pin,get} in bpf.c
and export bpf_map_pin to perf hook. I'll adjust my own patch.

I also have some patches to rework the samples/bpf/* code to use
libbpf instead of the sample code that is there, is it worth me
submitting that? It will need to wait for your patch to go in, plus a
merge with davem's tree.

On 2016/11/17 1:43, Joe Stringer wrote:

[SNIP]

/*
@@ -53,24 +60,71 @@ static int sys_bpf(enum bpf_cmd cmd, union bpf_attr
*attr,
return syscall(__NR_bpf, cmd, attr, size);
}
-int bpf_create_map(enum bpf_map_type map_type, int key_size,
- int value_size, int max_entries)
+int bpf_create_map(enum bpf_map_type map_type, int key_size, int
value_size,
+ int max_entries, int map_flags)
{
- union bpf_attr attr;
+ union bpf_attr attr = {
+ .map_type = map_type,
+ .key_size = key_size,
+ .value_size = value_size,
+ .max_entries = max_entries,
+ .map_flags = map_flags,
+ };
- memset(&attr, '\0', sizeof(attr));
+ return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+}


I lost map_flags in original bpf.c. Thanks to your patch. map_flags is
useful
when creating BPF_MAP_TYPE_PERCPU_HASH: BPF_F_NO_PREALLOC is meanful in this
case.
Do you want me to resubmit this piece as a separate patch or will you
address this?

Please send it.

Thank you.