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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Alan Maguire <alan.maguire@oracle.com>
Cc: acme@kernel.org, ast@kernel.org, andrii@kernel.org,
	daniel@iogearbox.net, quentin@isovalent.com, jolsa@kernel.org,
	martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
	john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
	haoluo@google.com, mykolal@fb.com, bpf@vger.kernel.org
Subject: Re: [PATCH v2 bpf-next 0/9] bpf: support BTF kind layout info, CRCs
Date: Fri, 16 Jun 2023 17:39:25 -0700	[thread overview]
Message-ID: <20230617003925.hrzvkiyasj4rwhdj@MacBook-Pro-8.local.dhcp.thefacebook.com> (raw)
In-Reply-To: <20230616171728.530116-1-alan.maguire@oracle.com>

On Fri, Jun 16, 2023 at 06:17:18PM +0100, Alan Maguire wrote:
> By separating parsing BTF from using all the information
> it provides, we allow BTF to encode new features even if
> they cannot be used.  This is helpful in particular for
> cases where newer tools for BTF generation run on an
> older kernel; BTF kinds may be present that the kernel
> cannot yet use, but at least it can parse the BTF
> provided.  Meanwhile userspace tools with newer libbpf
> may be able to use the newer information.

Overall looks great, but
why such narrow formatting? It's much less than 80.

> 
> The intent is to support encoding of kind layouts
> optionally so that tools like pahole can add this
> information.  So for each kind we record
> 
> - kind-related flags
> - length of singular element following struct btf_type
> - length of each of the btf_vlen() elements following
> 
> In addition we make space in the BTF header for
> CRC32s computed over the BTF along with a CRC for
> the base BTF; this allows split BTF to identify
> a mismatch explicitly.
> 
> The ideas here were discussed at [1], with further
> discussion at [2].
> 
> Future work can take more advantage of these features
> such as
> 
> - using base CRC to identify base/module BTF mismatch
>   explicitly
> - using absence of a base BTF CRC as evidence that
>   BTF is standalone

That's fine to have as a follow up, but with BTF_FLAG_CRC_SET
the kernel should check the crc.
Calling crc32c on modern cpus should be plenty fast.
It won't slow down btf verification.

  parent reply	other threads:[~2023-06-17  0:39 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-16 17:17 [PATCH v2 bpf-next 0/9] bpf: support BTF kind layout info, CRCs Alan Maguire
2023-06-16 17:17 ` [PATCH v2 bpf-next 1/9] btf: add kind layout encoding, crcs to UAPI Alan Maguire
2023-06-17  0:39   ` Alexei Starovoitov
2023-06-22 22:02   ` Andrii Nakryiko
2023-07-03 13:42     ` Alan Maguire
2023-07-05 23:48       ` Andrii Nakryiko
2023-07-20 20:18         ` Alan Maguire
2023-06-16 17:17 ` [PATCH v2 bpf-next 2/9] libbpf: support handling of kind layout section in BTF Alan Maguire
2023-06-22 22:02   ` Andrii Nakryiko
2023-06-16 17:17 ` [PATCH v2 bpf-next 3/9] libbpf: use kind layout to compute an unknown kind size Alan Maguire
2023-06-22 22:03   ` Andrii Nakryiko
2023-06-16 17:17 ` [PATCH v2 bpf-next 4/9] btf: support kernel parsing of BTF with kind layout Alan Maguire
2023-06-18 13:08   ` Jiri Olsa
2023-06-20  8:40     ` Alan Maguire
2023-06-22 22:03   ` Andrii Nakryiko
2023-06-16 17:17 ` [PATCH v2 bpf-next 5/9] libbpf: add kind layout encoding, crc support Alan Maguire
2023-06-19 23:24   ` Yonghong Song
2023-06-20  9:09     ` Alan Maguire
2023-06-20 14:41       ` Yonghong Song
2023-06-22 22:04   ` Andrii Nakryiko
2023-06-16 17:17 ` [PATCH v2 bpf-next 6/9] btf: generate BTF kind layout for vmlinux/module BTF Alan Maguire
2023-06-16 18:53   ` kernel test robot
2023-06-18 13:07   ` Jiri Olsa
2023-06-20  8:46     ` Alan Maguire
2023-06-16 17:17 ` [PATCH v2 bpf-next 7/9] bpftool: add BTF dump "format meta" to dump header/metadata Alan Maguire
2023-06-22 22:04   ` Andrii Nakryiko
2023-06-29 14:16   ` Quentin Monnet
2023-06-16 17:17 ` [PATCH v2 bpf-next 8/9] bpftool: update doc to describe bpftool btf dump .. format meta Alan Maguire
2023-06-29 14:16   ` Quentin Monnet
2023-06-16 17:17 ` [PATCH v2 bpf-next 9/9] selftests/bpf: test kind encoding/decoding Alan Maguire
2023-06-22 23:48   ` Andrii Nakryiko
2023-06-16 17:17 ` [PATCH dwarves] dwarves: encode BTF kind layout, crcs Alan Maguire
2023-06-17  0:39 ` Alexei Starovoitov [this message]
2023-06-20  8:41   ` [PATCH v2 bpf-next 0/9] bpf: support BTF kind layout info, CRCs Alan Maguire

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