[RFC PATCH v1 0/1] bpftool: Add generating command to C dumped file.

[RFC PATCH v1 0/1] bpftool: Add generating command to C dumped file.

[Francis Laniel]

Hi.


First, I hope you are fine and the same for your relatives.

In this patch, I added the command used to generate a BTF dump at the top of the
dump when outputting to C:
/*
 * File generated by bpftool using:
 * bpftool btf dump file /sys/kernel/btf/vmlinux format c
 * DO NOT EDIT.
 */

The goal of this is to first warn users this file must not be edited and also
to document the command used to get it.
The idea was gathered from a message posted on iovisor/bcc repository and from
message written by bpf2go when it generates a file [1, 2].

This patch is clearly not a big change which impacts the future of bpftool but
I think it could be welcomed.
If you see any way to improve it or have any question, feel free to ask.

Francis Laniel (1):
  bpftool: Add generating command to dumped file.

 tools/bpf/bpftool/btf.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)


Best regards and thank you in advance.
---
[1] https://github.com/iovisor/bcc/pull/4088#pullrequestreview-1032543916
[2] https://github.com/cilium/ebpf/blob/951bb28908d23e50fca063a2d51098ca028352bf/cmd/bpf2go/output.go#L21
-- 
2.25.1

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

[Francis Laniel]

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@linux.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]);
+	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

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

[sdf]

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@linux.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?
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 ?


> +	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

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

[Francis Laniel]

Hi.


Le mardi 12 juillet 2022, 22:47:40 CEST sdf@google.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@linux.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.