Subject: Re: [PATCH bpf-next v4 2/5] libbpf: Store map pin path and status in struct bpf_map

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 31 Oct 2019 18:26:48 +0100

Andrii Nakryiko <[email-masked]> writes:

> On Tue, Oct 29, 2019 at 12:39 PM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> From: Toke Høiland-Jørgensen <[email-masked]>
>>
>> Support storing and setting a pin path in struct bpf_map, which can be used
>> for automatic pinning. Also store the pin status so we can avoid attempts
>> to re-pin a map that has already been pinned (or reused from a previous
>> pinning).
>>
>> The behaviour of bpf_object__{un,}pin_maps() is changed so that if it is
>> called with a NULL path argument (which was previously illegal), it will
>> (un)pin only those maps that have a pin_path set.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
>> ---
>
> Looks good, thanks! Just some minor things to fix up below.
>
> Acked-by: Andrii Nakryiko <[email-masked]>
>
>>  tools/lib/bpf/libbpf.c   |  164 +++++++++++++++++++++++++++++++++++-----------
>>  tools/lib/bpf/libbpf.h   |    8 ++
>>  tools/lib/bpf/libbpf.map |    3 +
>>  3 files changed, 134 insertions(+), 41 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index ce5ef3ddd263..fd11f6aeb32c 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -226,6 +226,8 @@ struct bpf_map {
>>         void *priv;
>>         bpf_map_clear_priv_t clear_priv;
>>         enum libbpf_map_type libbpf_type;
>> +       char *pin_path;
>> +       bool pinned;
>>  };
>>
>>  struct bpf_secdata {
>> @@ -4025,47 +4027,119 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
>>         char *cp, errmsg[STRERR_BUFSIZE];
>>         int err;
>>
>> -       err = check_path(path);
>> -       if (err)
>> -               return err;
>> -
>>         if (map == NULL) {
>>                 pr_warn("invalid map pointer\n");
>>                 return -EINVAL;
>>         }
>>
>> -       if (bpf_obj_pin(map->fd, path)) {
>> -               cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
>> -               pr_warn("failed to pin map: %s\n", cp);
>> -               return -errno;
>> +       if (map->pin_path) {
>> +               if (path && strcmp(path, map->pin_path)) {
>> +                       pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
>> +                               bpf_map__name(map), map->pin_path, path);
>> +                       return -EINVAL;
>> +               } else if (map->pinned) {
>> +                       pr_debug("map '%s' already pinned at '%s'; not re-pinning\n",
>> +                                bpf_map__name(map), map->pin_path);
>> +                       return 0;
>> +               }
>
> `if (map->pinned)` check is the same in both branches, so I'd do it
> first, before this map->pin_path if/else.

But it's not. It's debug & return if pin_path is set, and an error
otherwise.

Will fix the rest of your nits :)

-Toke