Re: [PATCH bpf-next v3 4/4] selftests: Add tests for automatic map pinning

On Mon, 28 Oct 2019 15:32:26 +0000
Yonghong Song [off-list ref] wrote:

On 10/28/19 6:15 AM, Toke Høiland-Jørgensen wrote:

quoted

Jesper Dangaard Brouer [off-list ref] writes:
  

quoted

On Sun, 27 Oct 2019 21:53:19 +0100
Toke Høiland-Jørgensen [off-list ref] wrote:
 

quoted

diff --git a/tools/testing/selftests/bpf/progs/test_pinning.c b/tools/testing/selftests/bpf/progs/test_pinning.c
new file mode 100644
index 000000000000..ff2d7447777e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_pinning.c

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+int _version SEC("version") = 1;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+} pinmap SEC(".maps");  

So, this is the new BTF-defined maps syntax.

Please remind me, what version of LLVM do we need to compile this?  

No idea what the minimum version is. I'm running LLVM 9.0 :)  

LLVM 9.0 starts to support .maps.
There is no dependency on pahole.

LLVM 9.0.0 is still very new:
 - 19 September 2019: LLVM 9.0.0 is now available

For my XDP-tutorial[1], I cannot required people to have this new llvm
version.  But I would like to teach people about this new syntax (note,
I can upgrade libbpf version via git-submodule, and update bpf_helpers.h).

To Andrii, any recommendations on how I can do the transition? 

I'm thinking, it should be possible to define both ELF-object sections
SEC "maps" and ".maps" at the same time. But how does libbpf handle that?
(Who takes precedence?)


(Alternatively, I can detect the LLVM version, in the Makefile, and have
a #ifdef define in the code)
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

[1] https://github.com/xdp-project/xdp-tutorial