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* [RFC PATCH] bpftool btf: Add prefix option to dump C
@ 2020-07-22  5:43 Ian Rogers
  2020-07-22  6:57 ` Andrii Nakryiko
  0 siblings, 1 reply; 4+ messages in thread
From: Ian Rogers @ 2020-07-22  5:43 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, Andrii Nakryiko, John Fastabend, KP Singh,
	Quentin Monnet, Jakub Kicinski, Jiri Olsa,
	Toke Høiland-Jørgensen, netdev, bpf, linux-kernel
  Cc: Stanislav Fomichev, Ian Rogers

When bpftool dumps types and enum members into a header file for
inclusion the names match those in the original source. If the same
header file needs to be included in the original source and the bpf
program, the names of structs, unions, typedefs and enum members will
have naming collisions.

To avoid these collisions an approach is to redeclare the header file
types and enum members, which leads to duplication and possible
inconsistencies. Another approach is to use preprocessor macros
to rename conflicting names, but this can be cumbersome if there are
many conflicts.

This patch adds a prefix option for the dumped names. Use of this option
can avoid name conflicts and compile time errors.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 .../bpf/bpftool/Documentation/bpftool-btf.rst |  7 ++++++-
 tools/bpf/bpftool/btf.c                       | 18 ++++++++++++++---
 tools/lib/bpf/btf.h                           |  1 +
 tools/lib/bpf/btf_dump.c                      | 20 +++++++++++++------
 4 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
index 896f4c6c2870..85d66bc69634 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-btf.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
@@ -20,7 +20,7 @@ BTF COMMANDS
 =============
 
 |	**bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
-|	**bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
+|	**bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*] [**prefix** *PREFIX*]
 |	**bpftool** **btf help**
 |
 |	*BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
@@ -66,6 +66,11 @@ DESCRIPTION
 		  output format. Raw (**raw**) or C-syntax (**c**) output
 		  formats are supported.
 
+		  With the C-syntax format the **prefix** option can
+                  be used to prefix all identifiers and enum members
+                  with *PREFIX*. This is useful to avoid naming
+                  collisions.
+
 	**bpftool btf help**
 		  Print short help message.
 
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index fc9bc7a23db6..6a428636fa6f 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -379,12 +379,15 @@ 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, const char *name_prefix)
 {
 	struct btf_dump *d;
 	int err = 0, i;
+	struct btf_dump_opts opts = {
+		.name_prefix = name_prefix,
+	};
 
-	d = btf_dump__new(btf, NULL, NULL, btf_dump_printf);
+	d = btf_dump__new(btf, NULL, &opts, btf_dump_printf);
 	if (IS_ERR(d))
 		return PTR_ERR(d);
 
@@ -478,6 +481,7 @@ static int do_dump(int argc, char **argv)
 	bool dump_c = false;
 	__u32 btf_id = -1;
 	const char *src;
+	const char *c_prefix = NULL;
 	int fd = -1;
 	int err;
 
@@ -583,6 +587,14 @@ static int do_dump(int argc, char **argv)
 				goto done;
 			}
 			NEXT_ARG();
+		} else if (is_prefix(*argv, "prefix")) {
+			NEXT_ARG();
+			if (argc < 1 || !*argv) {
+				p_err("expecting value for 'prefix' option\n");
+				goto done;
+			}
+			c_prefix = *argv;
+			NEXT_ARG();
 		} else {
 			p_err("unrecognized option: '%s'", *argv);
 			goto done;
@@ -608,7 +620,7 @@ 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, c_prefix);
 	} else {
 		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
 	}
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 491c7b41ffdc..fea4baab00bd 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -117,6 +117,7 @@ struct btf_dump;
 
 struct btf_dump_opts {
 	void *ctx;
+	const char *name_prefix;
 };
 
 typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index e1c344504cae..baf2b4d82e1e 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -138,6 +138,7 @@ struct btf_dump *btf_dump__new(const struct btf *btf,
 	d->btf_ext = btf_ext;
 	d->printf_fn = printf_fn;
 	d->opts.ctx = opts ? opts->ctx : NULL;
+	d->opts.name_prefix = opts ? opts->name_prefix : NULL;
 
 	d->type_names = hashmap__new(str_hash_fn, str_equal_fn, NULL);
 	if (IS_ERR(d->type_names)) {
@@ -903,6 +904,7 @@ static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
 	const struct btf_enum *v = btf_enum(t);
 	__u16 vlen = btf_vlen(t);
 	const char *name;
+	const char *name_prefix = d->opts.name_prefix;
 	size_t dup_cnt;
 	int i;
 
@@ -912,17 +914,19 @@ static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
 
 	if (vlen) {
 		btf_dump_printf(d, " {");
+		if (!name_prefix)
+			name_prefix = "";
 		for (i = 0; i < vlen; i++, v++) {
 			name = btf_name_of(d, v->name_off);
 			/* enumerators share namespace with typedef idents */
 			dup_cnt = btf_dump_name_dups(d, d->ident_names, name);
 			if (dup_cnt > 1) {
-				btf_dump_printf(d, "\n%s%s___%zu = %u,",
-						pfx(lvl + 1), name, dup_cnt,
+				btf_dump_printf(d, "\n%s%s%s___%zu = %u,",
+						pfx(lvl + 1), name_prefix, name, dup_cnt,
 						(__u32)v->val);
 			} else {
-				btf_dump_printf(d, "\n%s%s = %u,",
-						pfx(lvl + 1), name,
+				btf_dump_printf(d, "\n%s%s%s = %u,",
+						pfx(lvl + 1), name_prefix, name,
 						(__u32)v->val);
 			}
 		}
@@ -1360,6 +1364,7 @@ static const char *btf_dump_resolve_name(struct btf_dump *d, __u32 id,
 	const struct btf_type *t = btf__type_by_id(d->btf, id);
 	const char *orig_name = btf_name_of(d, t->name_off);
 	const char **cached_name = &d->cached_names[id];
+	const char *prefix = d->opts.name_prefix;
 	size_t dup_cnt;
 
 	if (t->name_off == 0)
@@ -1369,11 +1374,14 @@ static const char *btf_dump_resolve_name(struct btf_dump *d, __u32 id,
 		return *cached_name ? *cached_name : orig_name;
 
 	dup_cnt = btf_dump_name_dups(d, name_map, orig_name);
-	if (dup_cnt > 1) {
+	if (dup_cnt > 1 || prefix) {
 		const size_t max_len = 256;
 		char new_name[max_len];
 
-		snprintf(new_name, max_len, "%s___%zu", orig_name, dup_cnt);
+		if (dup_cnt > 1)
+			snprintf(new_name, max_len, "%s%s___%zu", prefix, orig_name, dup_cnt);
+		else
+			snprintf(new_name, max_len, "%s%s", prefix, orig_name);
 		*cached_name = strdup(new_name);
 	}
 
-- 
2.28.0.rc0.105.gf9edc3c819-goog


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [RFC PATCH] bpftool btf: Add prefix option to dump C
  2020-07-22  5:43 [RFC PATCH] bpftool btf: Add prefix option to dump C Ian Rogers
@ 2020-07-22  6:57 ` Andrii Nakryiko
  2020-08-01  1:47   ` Ian Rogers
  0 siblings, 1 reply; 4+ messages in thread
From: Andrii Nakryiko @ 2020-07-22  6:57 UTC (permalink / raw)
  To: Ian Rogers
  Cc: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, Andrii Nakryiko, John Fastabend, KP Singh,
	Quentin Monnet, Jakub Kicinski, Jiri Olsa,
	Toke Høiland-Jørgensen, Networking, bpf, open list,
	Stanislav Fomichev

On Tue, Jul 21, 2020 at 10:44 PM Ian Rogers <irogers@google.com> wrote:
>
> When bpftool dumps types and enum members into a header file for
> inclusion the names match those in the original source. If the same
> header file needs to be included in the original source and the bpf
> program, the names of structs, unions, typedefs and enum members will
> have naming collisions.

vmlinux.h is not really intended to be used from user-space, because
it's incompatible with pretty much any other header that declares any
type. Ideally we should make this better, but that might require some
compiler support. We've been discussing with Yonghong extending Clang
with a compile-time check for whether some type is defined or not,
which would allow to guard every type and only declare it
conditionally, if it's missing. But that's just an idea at this point.

Regardless, vmlinux.h is also very much Clang-specific, and shouldn't
work well with GCC. Could you elaborate on the specifics of the use
case you have in mind? That could help me see what might be the right
solution. Thanks!

>
> To avoid these collisions an approach is to redeclare the header file
> types and enum members, which leads to duplication and possible
> inconsistencies. Another approach is to use preprocessor macros
> to rename conflicting names, but this can be cumbersome if there are
> many conflicts.
>
> This patch adds a prefix option for the dumped names. Use of this option
> can avoid name conflicts and compile time errors.
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  .../bpf/bpftool/Documentation/bpftool-btf.rst |  7 ++++++-
>  tools/bpf/bpftool/btf.c                       | 18 ++++++++++++++---
>  tools/lib/bpf/btf.h                           |  1 +
>  tools/lib/bpf/btf_dump.c                      | 20 +++++++++++++------
>  4 files changed, 36 insertions(+), 10 deletions(-)
>

[...]

> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index 491c7b41ffdc..fea4baab00bd 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -117,6 +117,7 @@ struct btf_dump;
>
>  struct btf_dump_opts {
>         void *ctx;
> +       const char *name_prefix;
>  };

BTW, we can't do that, this breaks ABI. btf_dump_opts were added
before we understood the problem of backward/forward  compatibility of
libbpf APIs, unfortunately.

>
>  typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index e1c344504cae..baf2b4d82e1e 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c

[...]

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [RFC PATCH] bpftool btf: Add prefix option to dump C
  2020-07-22  6:57 ` Andrii Nakryiko
@ 2020-08-01  1:47   ` Ian Rogers
  2020-08-01  3:47     ` Andrii Nakryiko
  0 siblings, 1 reply; 4+ messages in thread
From: Ian Rogers @ 2020-08-01  1:47 UTC (permalink / raw)
  To: Andrii Nakryiko
  Cc: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, Andrii Nakryiko, John Fastabend, KP Singh,
	Quentin Monnet, Jakub Kicinski, Jiri Olsa,
	Toke Høiland-Jørgensen, Networking, bpf, open list,
	Stanislav Fomichev

On Tue, Jul 21, 2020 at 11:58 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Tue, Jul 21, 2020 at 10:44 PM Ian Rogers <irogers@google.com> wrote:
> >
> > When bpftool dumps types and enum members into a header file for
> > inclusion the names match those in the original source. If the same
> > header file needs to be included in the original source and the bpf
> > program, the names of structs, unions, typedefs and enum members will
> > have naming collisions.
>
> vmlinux.h is not really intended to be used from user-space, because
> it's incompatible with pretty much any other header that declares any
> type. Ideally we should make this better, but that might require some
> compiler support. We've been discussing with Yonghong extending Clang
> with a compile-time check for whether some type is defined or not,
> which would allow to guard every type and only declare it
> conditionally, if it's missing. But that's just an idea at this point.

Thanks Andrii! We're not looking at user-space code but the BPF code.
The prefix idea comes from a way to solve this problem in C++ with
namespaces:

namespace vmlinux {
#include "vmlinux.h"
}

As the BPF programs are C code then the prefix acts like the
namespace. It seems strange to need to extend the language.

> Regardless, vmlinux.h is also very much Clang-specific, and shouldn't
> work well with GCC. Could you elaborate on the specifics of the use
> case you have in mind? That could help me see what might be the right
> solution. Thanks!

So the use-case is similar to btf_iter.h:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/bpf_iter.h
To avoid collisions with somewhat cleaner macro or not games.

Prompted by your concern I was looking into changing bpf_iter.h to use
a prefix to show what the difference would be like. I also think that
there may be issues with our kernel and tool set up that may mean that
the prefix is unnecessary, if I fix something else. Anyway, to give an
example I needed to build the selftests but this is failing for me.
What I see is:

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
$ cd bpf-next
$ make defconfig
$ cat >>.config <<EOF
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_BTF=y
EOF
$ make -j all
$ mkdir /tmp/selftests
$ make O=/tmp/selftests/ TARGETS=bpf kselftest
...
  CLANG    /tmp/selftests//kselftest/bpf/tools/build/bpftool/profiler.bpf.o
skeleton/profiler.bpf.c:18:21: error: invalid application of 'sizeof'
to an incomplete type 'struct bpf_perf_event_value'
        __uint(value_size, sizeof(struct bpf_perf_event_value));
                           ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Checking with bpftool the vmlinux lacks struct bpf_perf_event_value
but as this is unconditionally defined in bpf.h this seems wrong. Do
you have any suggestions and getting a working build?

> > To avoid these collisions an approach is to redeclare the header file
> > types and enum members, which leads to duplication and possible
> > inconsistencies. Another approach is to use preprocessor macros
> > to rename conflicting names, but this can be cumbersome if there are
> > many conflicts.
> >
> > This patch adds a prefix option for the dumped names. Use of this option
> > can avoid name conflicts and compile time errors.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  .../bpf/bpftool/Documentation/bpftool-btf.rst |  7 ++++++-
> >  tools/bpf/bpftool/btf.c                       | 18 ++++++++++++++---
> >  tools/lib/bpf/btf.h                           |  1 +
> >  tools/lib/bpf/btf_dump.c                      | 20 +++++++++++++------
> >  4 files changed, 36 insertions(+), 10 deletions(-)
> >
>
> [...]
>
> > diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> > index 491c7b41ffdc..fea4baab00bd 100644
> > --- a/tools/lib/bpf/btf.h
> > +++ b/tools/lib/bpf/btf.h
> > @@ -117,6 +117,7 @@ struct btf_dump;
> >
> >  struct btf_dump_opts {
> >         void *ctx;
> > +       const char *name_prefix;
> >  };
>
> BTW, we can't do that, this breaks ABI. btf_dump_opts were added
> before we understood the problem of backward/forward  compatibility of
> libbpf APIs, unfortunately.

This could be fixed by adding a "new" API for the parameter, which
would be unfortunate compared to just amending the existing API. There
may be solutions that are less duplicative.

Thanks,
Ian

> >
> >  typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
> > diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> > index e1c344504cae..baf2b4d82e1e 100644
> > --- a/tools/lib/bpf/btf_dump.c
> > +++ b/tools/lib/bpf/btf_dump.c
>
> [...]

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [RFC PATCH] bpftool btf: Add prefix option to dump C
  2020-08-01  1:47   ` Ian Rogers
@ 2020-08-01  3:47     ` Andrii Nakryiko
  0 siblings, 0 replies; 4+ messages in thread
From: Andrii Nakryiko @ 2020-08-01  3:47 UTC (permalink / raw)
  To: Ian Rogers
  Cc: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, Andrii Nakryiko, John Fastabend, KP Singh,
	Quentin Monnet, Jakub Kicinski, Jiri Olsa,
	Toke Høiland-Jørgensen, Networking, bpf, open list,
	Stanislav Fomichev

On Fri, Jul 31, 2020 at 6:47 PM Ian Rogers <irogers@google.com> wrote:
>
> On Tue, Jul 21, 2020 at 11:58 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Tue, Jul 21, 2020 at 10:44 PM Ian Rogers <irogers@google.com> wrote:
> > >
> > > When bpftool dumps types and enum members into a header file for
> > > inclusion the names match those in the original source. If the same
> > > header file needs to be included in the original source and the bpf
> > > program, the names of structs, unions, typedefs and enum members will
> > > have naming collisions.
> >
> > vmlinux.h is not really intended to be used from user-space, because
> > it's incompatible with pretty much any other header that declares any
> > type. Ideally we should make this better, but that might require some
> > compiler support. We've been discussing with Yonghong extending Clang
> > with a compile-time check for whether some type is defined or not,
> > which would allow to guard every type and only declare it
> > conditionally, if it's missing. But that's just an idea at this point.
>
> Thanks Andrii! We're not looking at user-space code but the BPF code.
> The prefix idea comes from a way to solve this problem in C++ with
> namespaces:
>
> namespace vmlinux {
> #include "vmlinux.h"
> }
>
> As the BPF programs are C code then the prefix acts like the
> namespace. It seems strange to need to extend the language.

This is a classic case of jumping to designing a solution without
discussing a real problem first :)

You don't need to use any of the kernel headers together with
vmlinux.h (and it won't work as well), because vmlinux.h is supposed
to have all the **used** types from the kernel. So BPF programs only
include vmlinux.h and few libbpf-provided headers with helpers. Which
is why I assumed that you are trying to use it from user-space. But
see below on what went wrong.

>
> > Regardless, vmlinux.h is also very much Clang-specific, and shouldn't
> > work well with GCC. Could you elaborate on the specifics of the use
> > case you have in mind? That could help me see what might be the right
> > solution. Thanks!
>
> So the use-case is similar to btf_iter.h:
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/bpf_iter.h
> To avoid collisions with somewhat cleaner macro or not games.
>
> Prompted by your concern I was looking into changing bpf_iter.h to use
> a prefix to show what the difference would be like. I also think that
> there may be issues with our kernel and tool set up that may mean that
> the prefix is unnecessary, if I fix something else. Anyway, to give an
> example I needed to build the selftests but this is failing for me.
> What I see is:
>
> $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
> $ cd bpf-next
> $ make defconfig
> $ cat >>.config <<EOF
> CONFIG_DEBUG_INFO=y
> CONFIG_DEBUG_INFO_BTF=y
> EOF
> $ make -j all
> $ mkdir /tmp/selftests
> $ make O=/tmp/selftests/ TARGETS=bpf kselftest
> ...
>   CLANG    /tmp/selftests//kselftest/bpf/tools/build/bpftool/profiler.bpf.o
> skeleton/profiler.bpf.c:18:21: error: invalid application of 'sizeof'
> to an incomplete type 'struct bpf_perf_event_value'
>         __uint(value_size, sizeof(struct bpf_perf_event_value));
>                            ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Checking with bpftool the vmlinux lacks struct bpf_perf_event_value
> but as this is unconditionally defined in bpf.h this seems wrong. Do
> you have any suggestions and getting a working build?

It is unconditionally defined in bpf.h, but unless kernel code really
uses that type for something, compiler won't generate DWARF
information for that type, which subsequently won't get into BTF.
Adding CONFIG_DEBUG_INFO_BTF=y ensures you get BTF type info
generated, but only for subsystems that were compiled into vmlinux
according to your kernel config.

In this case, default config doesn't enable CONFIG_BPF_EVENTS, which
is a requirement to compile kernel/trace/bpf_trace.c, which in turn
uses struct bpf_perf_event_value in the helper signature.

So the solution in your case would be to use a slightly richer kernel
config, which enables more of the BPF subsystem. You can check
selftests/bpf/config for a list of options we typically enable to run
of selftests, for instance.

>
> > > To avoid these collisions an approach is to redeclare the header file
> > > types and enum members, which leads to duplication and possible
> > > inconsistencies. Another approach is to use preprocessor macros
> > > to rename conflicting names, but this can be cumbersome if there are
> > > many conflicts.
> > >
> > > This patch adds a prefix option for the dumped names. Use of this option
> > > can avoid name conflicts and compile time errors.
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  .../bpf/bpftool/Documentation/bpftool-btf.rst |  7 ++++++-
> > >  tools/bpf/bpftool/btf.c                       | 18 ++++++++++++++---
> > >  tools/lib/bpf/btf.h                           |  1 +
> > >  tools/lib/bpf/btf_dump.c                      | 20 +++++++++++++------
> > >  4 files changed, 36 insertions(+), 10 deletions(-)
> > >
> >
> > [...]
> >
> > > diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> > > index 491c7b41ffdc..fea4baab00bd 100644
> > > --- a/tools/lib/bpf/btf.h
> > > +++ b/tools/lib/bpf/btf.h
> > > @@ -117,6 +117,7 @@ struct btf_dump;
> > >
> > >  struct btf_dump_opts {
> > >         void *ctx;
> > > +       const char *name_prefix;
> > >  };
> >
> > BTW, we can't do that, this breaks ABI. btf_dump_opts were added
> > before we understood the problem of backward/forward  compatibility of
> > libbpf APIs, unfortunately.
>
> This could be fixed by adding a "new" API for the parameter, which
> would be unfortunate compared to just amending the existing API. There
> may be solutions that are less duplicative.
>

Does ABI stability sucks for maintainers of the library? It absolutely
does! But we can't just go and break it.

> Thanks,
> Ian
>
> > >
> > >  typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args);
> > > diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> > > index e1c344504cae..baf2b4d82e1e 100644
> > > --- a/tools/lib/bpf/btf_dump.c
> > > +++ b/tools/lib/bpf/btf_dump.c
> >
> > [...]

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, back to index

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-22  5:43 [RFC PATCH] bpftool btf: Add prefix option to dump C Ian Rogers
2020-07-22  6:57 ` Andrii Nakryiko
2020-08-01  1:47   ` Ian Rogers
2020-08-01  3:47     ` Andrii Nakryiko

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