[PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Yinjun Zhang]

When reworking btf__get_from_id() in commit a19f93cfafdf the error
handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
if bpf_btf_get_fd_by_id() failed the error would not be propagated to
callers of btf__get_from_id(), after the rework it is. This lead to a
change in behavior in print_key_value() that now prints an error when
trying to lookup keys in maps with no btf available.

Fix this by following the way used in dumping maps to allow to look up
keys in no-btf maps, by which it decides whether and where to get the
btf info according to the btf value type.

Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
---
 tools/bpf/bpftool/map.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index cc530a229812..4fc772d66e3a 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
 	json_writer_t *btf_wtr;
 	struct btf *btf;
 
-	btf = btf__load_from_kernel_by_id(info->btf_id);
-	if (libbpf_get_error(btf)) {
-		p_err("failed to get btf");
+	btf = get_map_kv_btf(info);
+	if (libbpf_get_error(btf))
 		return;
-	}
 
 	if (json_output) {
 		print_entry_json(info, key, value, btf);
-- 
1.8.3.1

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Andrii Nakryiko]

On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> wrote:
>
> When reworking btf__get_from_id() in commit a19f93cfafdf the error
> handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> callers of btf__get_from_id(), after the rework it is. This lead to a
> change in behavior in print_key_value() that now prints an error when
> trying to lookup keys in maps with no btf available.
>
> Fix this by following the way used in dumping maps to allow to look up
> keys in no-btf maps, by which it decides whether and where to get the
> btf info according to the btf value type.
>
> Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> Signed-off-by: Simon Horman <simon.horman@corigine.com>
> ---
>  tools/bpf/bpftool/map.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index cc530a229812..4fc772d66e3a 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>         json_writer_t *btf_wtr;
>         struct btf *btf;
>
> -       btf = btf__load_from_kernel_by_id(info->btf_id);
> -       if (libbpf_get_error(btf)) {
> -               p_err("failed to get btf");
> +       btf = get_map_kv_btf(info);
> +       if (libbpf_get_error(btf))

See discussion in [0], it seems relevant.

  [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

>                 return;
> -       }
>
>         if (json_output) {
>                 print_entry_json(info, key, value, btf);
> --
> 1.8.3.1
>

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Jiri Olsa]

On Mon, Feb 07, 2022 at 09:42:25AM -0800, Andrii Nakryiko wrote:
> On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> wrote:
> >
> > When reworking btf__get_from_id() in commit a19f93cfafdf the error
> > handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> > if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> > callers of btf__get_from_id(), after the rework it is. This lead to a
> > change in behavior in print_key_value() that now prints an error when
> > trying to lookup keys in maps with no btf available.
> >
> > Fix this by following the way used in dumping maps to allow to look up
> > keys in no-btf maps, by which it decides whether and where to get the
> > btf info according to the btf value type.
> >
> > Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> > Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> > Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> > Signed-off-by: Simon Horman <simon.horman@corigine.com>
> > ---
> >  tools/bpf/bpftool/map.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> > index cc530a229812..4fc772d66e3a 100644
> > --- a/tools/bpf/bpftool/map.c
> > +++ b/tools/bpf/bpftool/map.c
> > @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
> >         json_writer_t *btf_wtr;
> >         struct btf *btf;
> >
> > -       btf = btf__load_from_kernel_by_id(info->btf_id);
> > -       if (libbpf_get_error(btf)) {
> > -               p_err("failed to get btf");
> > +       btf = get_map_kv_btf(info);
> > +       if (libbpf_get_error(btf))
> 
> See discussion in [0], it seems relevant.
> 
>   [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

I checked and this patch does not fix the problem for me,
but looks like similar issue, do you have test case for this?

mine is to dump any no-btf map with -p option

thanks,
jirka

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Jiri Olsa]

On Mon, Feb 07, 2022 at 06:57:20PM +0100, Jiri Olsa wrote:
> On Mon, Feb 07, 2022 at 09:42:25AM -0800, Andrii Nakryiko wrote:
> > On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> wrote:
> > >
> > > When reworking btf__get_from_id() in commit a19f93cfafdf the error
> > > handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> > > if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> > > callers of btf__get_from_id(), after the rework it is. This lead to a
> > > change in behavior in print_key_value() that now prints an error when
> > > trying to lookup keys in maps with no btf available.
> > >
> > > Fix this by following the way used in dumping maps to allow to look up
> > > keys in no-btf maps, by which it decides whether and where to get the
> > > btf info according to the btf value type.
> > >
> > > Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> > > Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> > > Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> > > Signed-off-by: Simon Horman <simon.horman@corigine.com>
> > > ---
> > >  tools/bpf/bpftool/map.c | 6 ++----
> > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> > > index cc530a229812..4fc772d66e3a 100644
> > > --- a/tools/bpf/bpftool/map.c
> > > +++ b/tools/bpf/bpftool/map.c
> > > @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
> > >         json_writer_t *btf_wtr;
> > >         struct btf *btf;
> > >
> > > -       btf = btf__load_from_kernel_by_id(info->btf_id);
> > > -       if (libbpf_get_error(btf)) {
> > > -               p_err("failed to get btf");
> > > +       btf = get_map_kv_btf(info);
> > > +       if (libbpf_get_error(btf))
> > 
> > See discussion in [0], it seems relevant.
> > 
> >   [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/
> 
> I checked and this patch does not fix the problem for me,
> but looks like similar issue, do you have test case for this?
> 
> mine is to dump any no-btf map with -p option

anyway I think your change should go in separately,
I can send change below (v2 for [0] above) on top of yours

thanks,
jirka


---
 tools/bpf/bpftool/map.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index c66a3c979b7a..8562add7417d 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -805,29 +805,28 @@ static int maps_have_btf(int *fds, int nb_fds)
 
 static struct btf *btf_vmlinux;
 
-static struct btf *get_map_kv_btf(const struct bpf_map_info *info)
+static int get_map_kv_btf(const struct bpf_map_info *info, struct btf **btf)
 {
-	struct btf *btf = NULL;
+	int err = 0;
 
 	if (info->btf_vmlinux_value_type_id) {
 		if (!btf_vmlinux) {
 			btf_vmlinux = libbpf_find_kernel_btf();
-			if (libbpf_get_error(btf_vmlinux))
+			err = libbpf_get_error(btf_vmlinux);
+			if (err) {
 				p_err("failed to get kernel btf");
+				return err;
+			}
 		}
-		return btf_vmlinux;
+		*btf = btf_vmlinux;
 	} else if (info->btf_value_type_id) {
-		int err;
-
-		btf = btf__load_from_kernel_by_id(info->btf_id);
-		err = libbpf_get_error(btf);
-		if (err) {
+		*btf = btf__load_from_kernel_by_id(info->btf_id);
+		err = libbpf_get_error(*btf);
+		if (err)
 			p_err("failed to get btf");
-			btf = ERR_PTR(err);
-		}
 	}
 
-	return btf;
+	return err;
 }
 
 static void free_map_kv_btf(struct btf *btf)
@@ -862,8 +861,7 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
 	prev_key = NULL;
 
 	if (wtr) {
-		btf = get_map_kv_btf(info);
-		err = libbpf_get_error(btf);
+		err = get_map_kv_btf(info, &btf);
 		if (err) {
 			goto exit_free;
 		}
@@ -1054,11 +1052,8 @@ static void print_key_value(struct bpf_map_info *info, void *key,
 	json_writer_t *btf_wtr;
 	struct btf *btf;
 
-	btf = btf__load_from_kernel_by_id(info->btf_id);
-	if (libbpf_get_error(btf)) {
-		p_err("failed to get btf");
+	if (get_map_kv_btf(info, &btf))
 		return;
-	}
 
 	if (json_output) {
 		print_entry_json(info, key, value, btf);
-- 
2.34.1

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Yonghong Song]

On 2/7/22 10:26 AM, Jiri Olsa wrote:
> On Mon, Feb 07, 2022 at 06:57:20PM +0100, Jiri Olsa wrote:
>> On Mon, Feb 07, 2022 at 09:42:25AM -0800, Andrii Nakryiko wrote:
>>> On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> wrote:
>>>>
>>>> When reworking btf__get_from_id() in commit a19f93cfafdf the error
>>>> handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
>>>> if bpf_btf_get_fd_by_id() failed the error would not be propagated to
>>>> callers of btf__get_from_id(), after the rework it is. This lead to a
>>>> change in behavior in print_key_value() that now prints an error when
>>>> trying to lookup keys in maps with no btf available.
>>>>
>>>> Fix this by following the way used in dumping maps to allow to look up
>>>> keys in no-btf maps, by which it decides whether and where to get the
>>>> btf info according to the btf value type.
>>>>
>>>> Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
>>>> Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
>>>> Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
>>>> Signed-off-by: Simon Horman <simon.horman@corigine.com>
>>>> ---
>>>>   tools/bpf/bpftool/map.c | 6 ++----
>>>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
>>>> index cc530a229812..4fc772d66e3a 100644
>>>> --- a/tools/bpf/bpftool/map.c
>>>> +++ b/tools/bpf/bpftool/map.c
>>>> @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>>>>          json_writer_t *btf_wtr;
>>>>          struct btf *btf;
>>>>
>>>> -       btf = btf__load_from_kernel_by_id(info->btf_id);
>>>> -       if (libbpf_get_error(btf)) {
>>>> -               p_err("failed to get btf");
>>>> +       btf = get_map_kv_btf(info);
>>>> +       if (libbpf_get_error(btf))
>>>
>>> See discussion in [0], it seems relevant.
>>>
>>>    [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

For the patch in the above link:

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index c66a3c979b7a..2ccf85042e75 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -862,6 +862,7 @@ map_dump(int fd, struct bpf_map_info *info, 
json_writer_t *wtr,
  	prev_key = NULL;

  	if (wtr) {
+		errno = 0;
  		btf = get_map_kv_btf(info);
  		err = libbpf_get_error(btf);
  		if (err) {
-- 

Do we know who sets non-zero errno in the above?
Maybe we can fix the issue in that place?

>>
>> I checked and this patch does not fix the problem for me,
>> but looks like similar issue, do you have test case for this?
>>
>> mine is to dump any no-btf map with -p option
> 
> anyway I think your change should go in separately,
> I can send change below (v2 for [0] above) on top of yours
> 
> thanks,
> jirka
> 
> 
> ---
>   tools/bpf/bpftool/map.c | 31 +++++++++++++------------------
>   1 file changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index c66a3c979b7a..8562add7417d 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -805,29 +805,28 @@ static int maps_have_btf(int *fds, int nb_fds)
>   
>   static struct btf *btf_vmlinux;
>   
> -static struct btf *get_map_kv_btf(const struct bpf_map_info *info)
> +static int get_map_kv_btf(const struct bpf_map_info *info, struct btf **btf)
>   {
> -	struct btf *btf = NULL;
> +	int err = 0;
>   
>   	if (info->btf_vmlinux_value_type_id) {
>   		if (!btf_vmlinux) {
>   			btf_vmlinux = libbpf_find_kernel_btf();
> -			if (libbpf_get_error(btf_vmlinux))
> +			err = libbpf_get_error(btf_vmlinux);
> +			if (err) {
>   				p_err("failed to get kernel btf");
> +				return err;
> +			}
>   		}
> -		return btf_vmlinux;
> +		*btf = btf_vmlinux;
>   	} else if (info->btf_value_type_id) {
> -		int err;
> -
> -		btf = btf__load_from_kernel_by_id(info->btf_id);
> -		err = libbpf_get_error(btf);
> -		if (err) {
> +		*btf = btf__load_from_kernel_by_id(info->btf_id);
> +		err = libbpf_get_error(*btf);
> +		if (err)
>   			p_err("failed to get btf");
> -			btf = ERR_PTR(err);
> -		}
>   	}
>   
> -	return btf;
> +	return err;
>   }
>   
>   static void free_map_kv_btf(struct btf *btf)
> @@ -862,8 +861,7 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
>   	prev_key = NULL;
>   
>   	if (wtr) {
> -		btf = get_map_kv_btf(info);
> -		err = libbpf_get_error(btf);
> +		err = get_map_kv_btf(info, &btf);
>   		if (err) {
>   			goto exit_free;
>   		}
> @@ -1054,11 +1052,8 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>   	json_writer_t *btf_wtr;
>   	struct btf *btf;
>   
> -	btf = btf__load_from_kernel_by_id(info->btf_id);
> -	if (libbpf_get_error(btf)) {
> -		p_err("failed to get btf");
> +	if (get_map_kv_btf(info, &btf))
>   		return;
> -	}
>   
>   	if (json_output) {
>   		print_entry_json(info, key, value, btf);

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Yinjun Zhang]

On Mon, Feb 07, 2022 at 07:26:29PM +0100, Jiri Olsa wrote:
> On Mon, Feb 07, 2022 at 06:57:20PM +0100, Jiri Olsa wrote:
> > On Mon, Feb 07, 2022 at 09:42:25AM -0800, Andrii Nakryiko wrote:
> > > On Mon, Feb 7, 2022 at 8:00 AM Yinjun Zhang <yinjun.zhang@corigine.com> wrote:
> > > >
> > > > When reworking btf__get_from_id() in commit a19f93cfafdf the error
> > > > handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> > > > if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> > > > callers of btf__get_from_id(), after the rework it is. This lead to a
> > > > change in behavior in print_key_value() that now prints an error when
> > > > trying to lookup keys in maps with no btf available.
> > > >
> > > > Fix this by following the way used in dumping maps to allow to look up
> > > > keys in no-btf maps, by which it decides whether and where to get the
> > > > btf info according to the btf value type.
> > > >
> > > > Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> > > > Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> > > > Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> > > > Signed-off-by: Simon Horman <simon.horman@corigine.com>
> > > > ---
> > > >  tools/bpf/bpftool/map.c | 6 ++----
> > > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> > > > index cc530a229812..4fc772d66e3a 100644
> > > > --- a/tools/bpf/bpftool/map.c
> > > > +++ b/tools/bpf/bpftool/map.c
> > > > @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
> > > >         json_writer_t *btf_wtr;
> > > >         struct btf *btf;
> > > >
> > > > -       btf = btf__load_from_kernel_by_id(info->btf_id);
> > > > -       if (libbpf_get_error(btf)) {
> > > > -               p_err("failed to get btf");
> > > > +       btf = get_map_kv_btf(info);
> > > > +       if (libbpf_get_error(btf))
> > > 
> > > See discussion in [0], it seems relevant.
> > > 
> > >   [0] https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/
> > 
> > I checked and this patch does not fix the problem for me,
> > but looks like similar issue, do you have test case for this?
> > 
> > mine is to dump any no-btf map with -p option
> 
> anyway I think your change should go in separately,
> I can send change below (v2 for [0] above) on top of yours
> 
> thanks,
> jirka
> 

Yeah, I agree they are separate issues, and my test case is also
simple, just lookup a key in a no-btf map, example:
# ./bpftool map create /sys/fs/bpf/xx type array key 4 value 4 entries 2 name def
# ./bpftool map lookup name def key 0 0 0 0
Error: failed to get btf

> 
> ---
>  tools/bpf/bpftool/map.c | 31 +++++++++++++------------------
>  1 file changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index c66a3c979b7a..8562add7417d 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -805,29 +805,28 @@ static int maps_have_btf(int *fds, int nb_fds)
>  
>  static struct btf *btf_vmlinux;
>  
> -static struct btf *get_map_kv_btf(const struct bpf_map_info *info)
> +static int get_map_kv_btf(const struct bpf_map_info *info, struct btf **btf)
>  {
> -	struct btf *btf = NULL;
> +	int err = 0;
>  
>  	if (info->btf_vmlinux_value_type_id) {
>  		if (!btf_vmlinux) {
>  			btf_vmlinux = libbpf_find_kernel_btf();
> -			if (libbpf_get_error(btf_vmlinux))
> +			err = libbpf_get_error(btf_vmlinux);
> +			if (err) {
>  				p_err("failed to get kernel btf");
> +				return err;
> +			}
>  		}
> -		return btf_vmlinux;
> +		*btf = btf_vmlinux;
>  	} else if (info->btf_value_type_id) {
> -		int err;
> -
> -		btf = btf__load_from_kernel_by_id(info->btf_id);
> -		err = libbpf_get_error(btf);
> -		if (err) {
> +		*btf = btf__load_from_kernel_by_id(info->btf_id);
> +		err = libbpf_get_error(*btf);
> +		if (err)
>  			p_err("failed to get btf");
> -			btf = ERR_PTR(err);
> -		}
>  	}
>  
> -	return btf;
> +	return err;
>  }
>  
>  static void free_map_kv_btf(struct btf *btf)
> @@ -862,8 +861,7 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
>  	prev_key = NULL;
>  
>  	if (wtr) {
> -		btf = get_map_kv_btf(info);
> -		err = libbpf_get_error(btf);
> +		err = get_map_kv_btf(info, &btf);
>  		if (err) {
>  			goto exit_free;
>  		}
> @@ -1054,11 +1052,8 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>  	json_writer_t *btf_wtr;
>  	struct btf *btf;
>  
> -	btf = btf__load_from_kernel_by_id(info->btf_id);
> -	if (libbpf_get_error(btf)) {
> -		p_err("failed to get btf");
> +	if (get_map_kv_btf(info, &btf))
>  		return;
> -	}
>  
>  	if (json_output) {
>  		print_entry_json(info, key, value, btf);
> -- 
> 2.34.1
> 

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[Jiri Olsa]

On Tue, Feb 08, 2022 at 12:00:25AM +0800, Yinjun Zhang wrote:
> When reworking btf__get_from_id() in commit a19f93cfafdf the error
> handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> callers of btf__get_from_id(), after the rework it is. This lead to a
> change in behavior in print_key_value() that now prints an error when
> trying to lookup keys in maps with no btf available.
> 
> Fix this by following the way used in dumping maps to allow to look up
> keys in no-btf maps, by which it decides whether and where to get the
> btf info according to the btf value type.
> 
> Fixes: a19f93cfafdf ("libbpf: Add internal helper to load BTF data by FD")
> Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> Signed-off-by: Simon Horman <simon.horman@corigine.com>

once this one gets merged, I'd send this fix on top of that:
  https://lore.kernel.org/bpf/20220204225823.339548-3-jolsa@kernel.org/

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka


> ---
>  tools/bpf/bpftool/map.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index cc530a229812..4fc772d66e3a 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1054,11 +1054,9 @@ static void print_key_value(struct bpf_map_info *info, void *key,
>  	json_writer_t *btf_wtr;
>  	struct btf *btf;
>  
> -	btf = btf__load_from_kernel_by_id(info->btf_id);
> -	if (libbpf_get_error(btf)) {
> -		p_err("failed to get btf");
> +	btf = get_map_kv_btf(info);
> +	if (libbpf_get_error(btf))
>  		return;
> -	}
>  
>  	if (json_output) {
>  		print_entry_json(info, key, value, btf);
> -- 
> 1.8.3.1
> 

Re: [PATCH bpf] bpftool: fix the error when lookup in no-btf maps

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Tue,  8 Feb 2022 00:00:25 +0800 you wrote:
> When reworking btf__get_from_id() in commit a19f93cfafdf the error
> handling when calling bpf_btf_get_fd_by_id() changed. Before the rework
> if bpf_btf_get_fd_by_id() failed the error would not be propagated to
> callers of btf__get_from_id(), after the rework it is. This lead to a
> change in behavior in print_key_value() that now prints an error when
> trying to lookup keys in maps with no btf available.
> 
> [...]

Here is the summary with links:
  - [bpf] bpftool: fix the error when lookup in no-btf maps
    https://git.kernel.org/bpf/bpf-next/c/edc21dc909c6

You are awesome, thank you!
-- 
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