netdev - Re: [PATCH bpf-next 5/5] tools/bpftool: add support for in-kernel and named BTF in `btf show`

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Date:   Mon, 9 Nov 2020 16:42:58 +0000 (GMT)
From:   Alan Maguire <alan.maguire@...cle.com>
To:     Andrii Nakryiko <andrii@...nel.org>
cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, kernel-team@...com,
        linux-kernel@...r.kernel.org, rafael@...nel.org, jeyu@...nel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH bpf-next 5/5] tools/bpftool: add support for in-kernel
 and named BTF in `btf show`

On Thu, 5 Nov 2020, Andrii Nakryiko wrote:

> Display vmlinux BTF name and kernel module names when listing available BTFs
> on the system.
> 
> In human-readable output mode, module BTFs are reported with "name
> [module-name]", while vmlinux BTF will be reported as "name [vmlinux]".
> Square brackets are added by bpftool and follow kernel convention when
> displaying modules in human-readable text outputs.
> 

I had a go at testing this and all looks good, but I was curious
if  "bpftool btf dump" is expected to work with module BTF? I see
the various modules in /sys/kernel/btf, but if I run:

# bpftool btf dump file /sys/kernel/btf/ixgbe
Error: failed to load BTF from /sys/kernel/btf/ixgbe: Invalid argument

...while it still works for vmlinux:

# bpftool btf dump file /sys/kernel/btf/vmlinux
[1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 
encoding=(none)
...

"bpftool btf show" works for ixgbe:

# bpftool btf show|grep ixgbe
19: name [ixgbe]  size 182074B

Is this perhaps not expected to work yet? (I updated pahole
to the latest changes etc and BTF generation seemed to work
fine for modules during kernel build).

For the "bpftool btf show" functionality, feel free to add

Tested-by: Alan Maguire <alan.maguire@...cle.com>

Thanks!

Alan