[PATCH v2 0/2] Print map ID on successful creation

[PATCH v2 0/2] Print map ID on successful creation

[Harshit Mogalapalli]

Hi all,

I have tried looking at an issue from the bpftool repository:
https://github.com/libbpf/bpftool/issues/121 and this RFC tries to add
that enhancement.

Summary: Currently when a map creation is successful there is no message
on the terminal, printing IDs on successful creation of maps can help
notify the user and can be used in CI/CD.

The first patch adds the logic for printing and the second patch adds a
simple selftest for the same.

The github issue is not fully solved with these two patches, as there
are other bpf objects that might need similar additions. Would
appreciate any inputs on this.

Thank you very much.

V1 --> V2: PATCH 1 updated [Thanks Yonghong for suggesting better way of
error handling with a new label for close(fd); instead of calling
multiple times]

Regards,
Harshit

Harshit Mogalapalli (2):
  bpftool: Print map ID upon creation and support JSON output
  selftests/bpf: Add test for bpftool map ID printing

 tools/bpf/bpftool/map.c                       | 21 ++++++++---
 .../testing/selftests/bpf/test_bpftool_map.sh | 36 +++++++++++++++++++
 2 files changed, 53 insertions(+), 4 deletions(-)

-- 
2.50.1

[PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output

[Harshit Mogalapalli]

It is useful to print map ID on successful creation.

JSON case:
$ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 128 name map4
{"id":12}

Generic case:
$ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 128 name map5
Map successfully created with ID: 15

Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
---
 tools/bpf/bpftool/map.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index c9de44a45778..80c96b33b553 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -1251,6 +1251,8 @@ static int do_create(int argc, char **argv)
 	LIBBPF_OPTS(bpf_map_create_opts, attr);
 	enum bpf_map_type map_type = BPF_MAP_TYPE_UNSPEC;
 	__u32 key_size = 0, value_size = 0, max_entries = 0;
+	struct bpf_map_info map_info = {};
+	__u32 map_info_len = sizeof(map_info);
 	const char *map_name = NULL;
 	const char *pinfile;
 	int err = -1, fd;
@@ -1353,13 +1355,24 @@ static int do_create(int argc, char **argv)
 	}
 
 	err = do_pin_fd(fd, pinfile);
-	close(fd);
 	if (err)
-		goto exit;
+		goto close_fd;
 
-	if (json_output)
-		jsonw_null(json_wtr);
+	err = bpf_obj_get_info_by_fd(fd, &map_info, &map_info_len);
+	if (err) {
+		p_err("Failed to fetch map info: %s\n", strerror(errno));
+		goto close_fd;
+	}
 
+	if (json_output) {
+		jsonw_start_object(json_wtr);
+		jsonw_int_field(json_wtr, "id", map_info.id);
+		jsonw_end_object(json_wtr);
+	} else {
+		printf("Map successfully created with ID: %u\n", map_info.id);
+	}
+close_fd:
+	close(fd);
 exit:
 	if (attr.inner_map_fd > 0)
 		close(attr.inner_map_fd);
-- 
2.50.1

Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output

[Yonghong Song]

On 10/30/25 2:06 PM, Harshit Mogalapalli wrote:
> It is useful to print map ID on successful creation.
>
> JSON case:
> $ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 128 name map4
> {"id":12}
>
> Generic case:
> $ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 128 name map5
> Map successfully created with ID: 15
>
> Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output

[Quentin Monnet]

2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
<harshit.m.mogalapalli@oracle.com>
> It is useful to print map ID on successful creation.
> 
> JSON case:
> $ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 128 name map4
> {"id":12}
> 
> Generic case:
> $ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 128 name map5
> Map successfully created with ID: 15
> 
> Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
> ---
>  tools/bpf/bpftool/map.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index c9de44a45778..80c96b33b553 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1251,6 +1251,8 @@ static int do_create(int argc, char **argv)
>  	LIBBPF_OPTS(bpf_map_create_opts, attr);
>  	enum bpf_map_type map_type = BPF_MAP_TYPE_UNSPEC;
>  	__u32 key_size = 0, value_size = 0, max_entries = 0;
> +	struct bpf_map_info map_info = {};
> +	__u32 map_info_len = sizeof(map_info);
>  	const char *map_name = NULL;
>  	const char *pinfile;
>  	int err = -1, fd;
> @@ -1353,13 +1355,24 @@ static int do_create(int argc, char **argv)
>  	}
>  
>  	err = do_pin_fd(fd, pinfile);
> -	close(fd);
>  	if (err)
> -		goto exit;
> +		goto close_fd;
>  
> -	if (json_output)
> -		jsonw_null(json_wtr);
> +	err = bpf_obj_get_info_by_fd(fd, &map_info, &map_info_len);
> +	if (err) {
> +		p_err("Failed to fetch map info: %s\n", strerror(errno));


Nit: Please remove the line break ('\n') here, p_err() already adds it.


> +		goto close_fd;
> +	}
>  
> +	if (json_output) {
> +		jsonw_start_object(json_wtr);
> +		jsonw_int_field(json_wtr, "id", map_info.id);
> +		jsonw_end_object(json_wtr);


I've been wondering if we should have some parent object like
'{"map_created": { "id": 15 }}' in case we later add more output, but I
can't really see a good use case at the moment, I'm probably
overthinking it... So I'm good with the current output. Thanks for this!

With the line break removed:

Reviewed-by: Quentin Monnet <qmo@kernel.org>

Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output

[Harshit Mogalapalli]

Hi Quentin,

On 01/11/25 22:29, Quentin Monnet wrote:
> 2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
> <harshit.m.mogalapalli@oracle.com>
>> It is useful to print map ID on successful creation.
>>
>> JSON case:
>> $ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 128 name map4
>> {"id":12}
>>
>> Generic case:
>> $ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 128 name map5
>> Map successfully created with ID: 15
>>
>> Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
>> ---
>>   tools/bpf/bpftool/map.c | 21 +++++++++++++++++----
>>   1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
>> index c9de44a45778..80c96b33b553 100644
>> --- a/tools/bpf/bpftool/map.c
>> +++ b/tools/bpf/bpftool/map.c
>> @@ -1251,6 +1251,8 @@ static int do_create(int argc, char **argv)
>>   	LIBBPF_OPTS(bpf_map_create_opts, attr);
>>   	enum bpf_map_type map_type = BPF_MAP_TYPE_UNSPEC;
>>   	__u32 key_size = 0, value_size = 0, max_entries = 0;
>> +	struct bpf_map_info map_info = {};
>> +	__u32 map_info_len = sizeof(map_info);
>>   	const char *map_name = NULL;
>>   	const char *pinfile;
>>   	int err = -1, fd;
>> @@ -1353,13 +1355,24 @@ static int do_create(int argc, char **argv)
>>   	}
>>   
>>   	err = do_pin_fd(fd, pinfile);
>> -	close(fd);
>>   	if (err)
>> -		goto exit;
>> +		goto close_fd;
>>   
>> -	if (json_output)
>> -		jsonw_null(json_wtr);
>> +	err = bpf_obj_get_info_by_fd(fd, &map_info, &map_info_len);
>> +	if (err) {
>> +		p_err("Failed to fetch map info: %s\n", strerror(errno));
> 
> 
> Nit: Please remove the line break ('\n') here, p_err() already adds it.
> 

Ah thanks for spotting that, will do.

> 
>> +		goto close_fd;
>> +	}
>>   
>> +	if (json_output) {
>> +		jsonw_start_object(json_wtr);
>> +		jsonw_int_field(json_wtr, "id", map_info.id);
>> +		jsonw_end_object(json_wtr);
> 
> 
> I've been wondering if we should have some parent object like
> '{"map_created": { "id": 15 }}' in case we later add more output, but I
> can't really see a good use case at the moment, I'm probably
> overthinking it... So I'm good with the current output. Thanks for this!
> 

Thanks a lot for the review.

> With the line break removed:
> 

Sure will send a next version with updates to p_err and selftest(to not 
echo messages on success)

> Reviewed-by: Quentin Monnet <qmo@kernel.org>
Regards,
Harshit

[PATCH v2 2/2] selftests/bpf: Add test for bpftool map ID printing

[Harshit Mogalapalli]

Add selftest to check if Map ID is printed on successful creation in
both plain text and json formats.

Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
---
 .../testing/selftests/bpf/test_bpftool_map.sh | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_bpftool_map.sh b/tools/testing/selftests/bpf/test_bpftool_map.sh
index 515b1df0501e..013a64e96cbf 100755
--- a/tools/testing/selftests/bpf/test_bpftool_map.sh
+++ b/tools/testing/selftests/bpf/test_bpftool_map.sh
@@ -361,6 +361,40 @@ test_map_access_with_btf_list() {
 	fi
 }
 
+# Function to test map ID printing
+# Parameters:
+#   $1: bpftool path
+#   $2: BPF_DIR
+test_map_id_printing() {
+	local bpftool_path="$1"
+	local bpf_dir="$2"
+	local test_map_name="test_map_id"
+	local test_map_path="$bpf_dir/$test_map_name"
+
+	local output
+	output=$("$bpftool_path" map create "$test_map_path" type hash key 4 \
+		value 8 entries 128 name "$test_map_name")
+	if echo "$output" | grep -q "Map successfully created with ID:"; then
+		echo "PASS: Map ID printed in plain text output."
+	else
+		echo "FAIL: Map ID not printed in plain text output."
+		exit 1
+	fi
+
+	rm -f "$test_map_path"
+
+	output=$("$bpftool_path" map create "$test_map_path" type hash key 4 \
+		value 8 entries 128 name "$test_map_name" --json)
+	if echo "$output" | jq -e 'has("id")' >/dev/null 2>&1; then
+		echo "PASS: Map ID printed in JSON output."
+	else
+		echo "FAIL: Map ID not printed in JSON output."
+		exit 1
+	fi
+
+	rm -f "$test_map_path"
+}
+
 set -eu
 
 trap cleanup_skip EXIT
@@ -395,4 +429,6 @@ test_map_creation_and_map_of_maps "$BPFTOOL_PATH" "$BPF_DIR"
 
 test_map_access_with_btf_list "$BPFTOOL_PATH"
 
+test_map_id_printing "$BPFTOOL_PATH" "$BPF_DIR"
+
 exit 0
-- 
2.50.1

Re: [PATCH v2 2/2] selftests/bpf: Add test for bpftool map ID printing

[Quentin Monnet]

2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
<harshit.m.mogalapalli@oracle.com>
> Add selftest to check if Map ID is printed on successful creation in
> both plain text and json formats.
> 
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
> ---
>  .../testing/selftests/bpf/test_bpftool_map.sh | 36 +++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/test_bpftool_map.sh b/tools/testing/selftests/bpf/test_bpftool_map.sh
> index 515b1df0501e..013a64e96cbf 100755
> --- a/tools/testing/selftests/bpf/test_bpftool_map.sh
> +++ b/tools/testing/selftests/bpf/test_bpftool_map.sh
> @@ -361,6 +361,40 @@ test_map_access_with_btf_list() {
>  	fi
>  }
>  
> +# Function to test map ID printing
> +# Parameters:
> +#   $1: bpftool path
> +#   $2: BPF_DIR
> +test_map_id_printing() {
> +	local bpftool_path="$1"
> +	local bpf_dir="$2"
> +	local test_map_name="test_map_id"
> +	local test_map_path="$bpf_dir/$test_map_name"
> +
> +	local output
> +	output=$("$bpftool_path" map create "$test_map_path" type hash key 4 \
> +		value 8 entries 128 name "$test_map_name")
> +	if echo "$output" | grep -q "Map successfully created with ID:"; then
> +		echo "PASS: Map ID printed in plain text output."
> +	else
> +		echo "FAIL: Map ID not printed in plain text output."
> +		exit 1


Other tests in the file print a message only on failure, without a
"FAIL:" prefix. Could you do the same, for consistency and brevity? Same
for the JSON test.

Thanks,
Quentin

Re: [PATCH v2 0/2] Print map ID on successful creation

[Quentin Monnet]

2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
<harshit.m.mogalapalli@oracle.com>
> Hi all,
> 
> I have tried looking at an issue from the bpftool repository:
> https://github.com/libbpf/bpftool/issues/121 and this RFC tries to add


This is not longer a RFC :)


> that enhancement.
> 
> Summary: Currently when a map creation is successful there is no message
> on the terminal, printing IDs on successful creation of maps can help
> notify the user and can be used in CI/CD.
> 
> The first patch adds the logic for printing and the second patch adds a
> simple selftest for the same.
> 
> The github issue is not fully solved with these two patches, as there
> are other bpf objects that might need similar additions. Would
> appreciate any inputs on this.


What's your question, exactly?

Thanks,
Quentin

Re: [PATCH v2 0/2] Print map ID on successful creation

[Harshit Mogalapalli]

Hi Quentin,

On 01/11/25 22:29, Quentin Monnet wrote:
> 2025-10-30 14:06 UTC-0700 ~ Harshit Mogalapalli
> <harshit.m.mogalapalli@oracle.com>
>> Hi all,
>>
>> I have tried looking at an issue from the bpftool repository:
>> https://github.com/libbpf/bpftool/issues/121 and this RFC tries to add
> 
> 
> This is not longer a RFC :)
> 

Oh, right, I used part of it from my RFC cover letter, sorry about that.

> 
>> that enhancement.
>>
>> Summary: Currently when a map creation is successful there is no message
>> on the terminal, printing IDs on successful creation of maps can help
>> notify the user and can be used in CI/CD.
>>
>> The first patch adds the logic for printing and the second patch adds a
>> simple selftest for the same.
>>
>> The github issue is not fully solved with these two patches, as there
>> are other bpf objects that might need similar additions. Would
>> appreciate any inputs on this.
> 
> 
> What's your question, exactly?
> 
If I understand the issue correctly, the goal is to improve usability
and CI support by printing IDs or other relevant information to the
terminal upon creation of BPF objects, instead of producing no output as
is currently the case. For maps, printing the map ID on creation is
particularly helpful.

In addition to maps, I believe it would be beneficial to print the ID 
when loading a program. I am currently working on implementing this 
enhancement.

Are there any other BPF objects where displaying additional information 
(such as IDs or relevant metadata) on the terminal would be useful?


Thank you!


Regards,
Harshit
  > Thanks,
> Quentin