linux-kernel - Re: [RFC PATCH v1 1/1] bpftool: Add generating command to C dumped file.

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Date:   Wed, 13 Jul 2022 15:40:22 +0200
From:   Francis Laniel <flaniel@...ux.microsoft.com>
To:     sdf@...gle.com
Cc:     bpf@...r.kernel.org, Quentin Monnet <quentin@...valent.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 1/1] bpftool: Add generating command to C dumped file.

Hi.


Le mardi 12 juillet 2022, 22:47:40 CEST sdf@...gle.com a écrit :
> On 07/12, Francis Laniel wrote:
> > This commit adds the following lines to file generated by dump:
> > /*
> > 
> >   * File generated by bpftool using:
> >   * bpftool btf dump file /sys/kernel/btf/vmlinux format c
> >   * DO NOT EDIT.
> >   */
> > 
> > This warns users to not edit the file and documents the command used to
> > generate the file.
> > 
> > Signed-off-by: Francis Laniel <flaniel@...ux.microsoft.com>
> > ---
> > 
> >   tools/bpf/bpftool/btf.c | 16 ++++++++++++++--
> >   1 file changed, 14 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > index 7e6accb9d9f7..eecfc27370c3 100644
> > --- a/tools/bpf/bpftool/btf.c
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -415,7 +415,8 @@ static void __printf(2, 0) btf_dump_printf(void *ctx,
> > 
> >   }
> >   
> >   static int dump_btf_c(const struct btf *btf,
> > 
> > -		      __u32 *root_type_ids, int root_type_cnt)
> > +		      __u32 *root_type_ids, int root_type_cnt,
> > +		      int argc, char **argv)
> > 
> >   {
> >   
> >   	struct btf_dump *d;
> >   	int err = 0, i;
> > 
> > @@ -425,6 +426,14 @@ static int dump_btf_c(const struct btf *btf,
> > 
> >   	if (err)
> >   	
> >   		return err;
> > 
> > +	printf("/*\n");
> > +	printf(" * File generated by bpftool using:\n");
> > +	printf(" * bpftool btf dump");
> 
> [..]
> 
> > +	for (i = 0; i < argc; i++)
> > +		printf(" %s", argv[i]);
> 
> Do we really need that complexity to preserve the arguments?

I was also a bit sceptickal when I first wrote as I found this code a bit 
complex for not so much added value.
But in my case, I do not use bpftool often, so having the command documented 
in the generated file would have been useful.
I will just find another way to document (or I think now I will not forget it 
anymore since this series).

> For skeletons we're simply doing:
> 
> 	/* THIS FILE IS AUTOGENERATED BY BPFTOOL! */
> 
> So probably the same should be fine here?
> 
> Also, while at it, might be worth adding SPDX license comment? So let's
> align with whatever we have in gen.c ?

I will send a v2 aligned on skeletons in no more than 15 minutes.

> > +	printf("\n");
> > +	printf(" * DO NOT EDIT.\n");
> > +	printf(" */\n");
> > 
> >   	printf("#ifndef __VMLINUX_H__\n");
> >   	printf("#define __VMLINUX_H__\n");
> >   	printf("\n");
> > 
> > @@ -507,8 +516,10 @@ static bool btf_is_kernel_module(__u32 btf_id)
> > 
> >   static int do_dump(int argc, char **argv)
> >   {
> >   
> >   	struct btf *btf = NULL, *base = NULL;
> > 
> > +	char **orig_argv = argv;
> > 
> >   	__u32 root_type_ids[2];
> >   	int root_type_cnt = 0;
> > 
> > +	int orig_argc = argc;
> > 
> >   	bool dump_c = false;
> >   	__u32 btf_id = -1;
> >   	const char *src;
> > 
> > @@ -649,7 +660,8 @@ static int do_dump(int argc, char **argv)
> > 
> >   			err = -ENOTSUP;
> >   			goto done;
> >   		
> >   		}
> > 
> > -		err = dump_btf_c(btf, root_type_ids, root_type_cnt);
> > +		err = dump_btf_c(btf, root_type_ids, root_type_cnt,
> > +				 orig_argc, orig_argv);
> > 
> >   	} else {
> >   	
> >   		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
> >   	
> >   	}
> > 
> > --
> > 2.25.1


Best regards.