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

Harshit Mogalapalli posted 2 patches 3 months, 1 week ago
There is a newer version of this series
[PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output
Posted by Harshit Mogalapalli 3 months, 1 week ago 
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
Posted by Quentin Monnet 3 months, 1 week ago 
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
Posted by Harshit Mogalapalli 3 months, 1 week ago 
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
Re: [PATCH v2 1/2] bpftool: Print map ID upon creation and support JSON output
Posted by Yonghong Song 3 months, 1 week ago 

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>

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