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Date: Thu, 9 Aug 2018 21:44:04 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Yonghong Song <yhs@...com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: ast@...com, netdev@...r.kernel.org, kernel-team@...com,
jakub.kicinski@...ronome.com
Subject: Re: [PATCH bpf] bpf: fix bpffs non-array map seq_show issue
On 08/09/2018 07:54 PM, Yonghong Song wrote:
> On 8/9/18 10:02 AM, Daniel Borkmann wrote:
>> On 08/09/2018 06:55 PM, Yonghong Song wrote:
>>> On 8/9/18 8:59 AM, Daniel Borkmann wrote:
>>>> On 08/09/2018 05:15 PM, Yonghong Song wrote:
>>>>> On 8/9/18 7:24 AM, Daniel Borkmann wrote:
>>>>>> On 08/09/2018 05:55 AM, Yonghong Song wrote:
>>>>>>> On 8/8/18 7:25 PM, Alexei Starovoitov wrote:
>>>>>>>> On Wed, Aug 08, 2018 at 06:25:19PM -0700, Yonghong Song wrote:
>>>>>>>>> In function map_seq_next() of kernel/bpf/inode.c,
>>>>>>>>> the first key will be the "0" regardless of the map type.
>>>>>>>>> This works for array. But for hash type, if it happens
>>>>>>>>> key "0" is in the map, the bpffs map show will miss
>>>>>>>>> some items if the key "0" is not the first element of
>>>>>>>>> the first bucket.
>>>>>>>>>
>>>>>>>>> This patch fixed the issue by guaranteeing to get
>>>>>>>>> the first element, if the seq_show is just started,
>>>>>>>>> by passing NULL pointer key to map_get_next_key() callback.
>>>>>>>>> This way, no missing elements will occur for
>>>>>>>>> bpffs hash table show even if key "0" is in the map.
>>>>>>>
>>>>>>> Currently, map_seq_show_elem callback is only implemented
>>>>>>> for arraymap. So the problem actually is not exposed.
>>>>>>>
>>>>>>> The issue is discovered when I tried to implement
>>>>>>> map_seq_show_elem for hash maps, and I will have followup
>>>>>>> patches for it.
>>>>
>>>> Btw, on that note, I would also prefer if we could decouple
>>>> BTF from the map_seq_show_elem() as there is really no reason
>>>> to have it on a per-map. I had a patch below which would enable
>>>> it for all map types generically, and bpftool works out of the
>>>> box for it. Also, array doesn't really have to be 'int' type
>>>> enforced as long as it's some data structure with 4 bytes, it's
>>>> all fine, so this can be made fully generic (we only eventually
>>>> care about the match in size).
>>>
>>> I agree with a generic map_check_btf as mostly we only care about size
>>> and this change should enable btftool btf based pretty print for hash/lru_hash tables.
>>
>> Yep, agree, the below output from bpftool is from test_xdp_noinline.o
>> where both work with it.
>>
>>>> From 0a8be27cbc2ac0c6fc2632865b5afe37222a1fc7 Mon Sep 17 00:00:00 2001
>>>> Message-Id: <0a8be27cbc2ac0c6fc2632865b5afe37222a1fc7.1533830053.git.daniel@...earbox.net>
>>>> From: Daniel Borkmann <daniel@...earbox.net>
>>>> Date: Thu, 9 Aug 2018 16:50:21 +0200
>>>> Subject: [PATCH bpf-next] bpf, btf: enable for all maps
>>>>
>>>> # bpftool m dump id 19
>>>> [{
>>>> "key": {
>>>> "": {
>>>> "vip": 0,
>>>> "vipv6": []
>>>> },
>>>> "port": 0,
>>>> "family": 0,
>>>> "proto": 0
>>>> },
>>>> "value": {
>>>> "flags": 0,
>>>> "vip_num": 0
>>>> }
>>>> }
>>>> ]
>>>>
>>>> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
>>>> ---
>>>> include/linux/bpf.h | 4 +---
>>>> kernel/bpf/arraymap.c | 27 ---------------------------
>>>> kernel/bpf/inode.c | 3 ++-
>>>> kernel/bpf/syscall.c | 24 ++++++++++++++++++++----
>>>> 4 files changed, 23 insertions(+), 35 deletions(-)
>>>>
>>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>>> index cd8790d..91aa4be 100644
>>>> --- a/include/linux/bpf.h
>>>> +++ b/include/linux/bpf.h
>>>> @@ -48,8 +48,6 @@ struct bpf_map_ops {
>>>> u32 (*map_fd_sys_lookup_elem)(void *ptr);
>>>> void (*map_seq_show_elem)(struct bpf_map *map, void *key,
>>>> struct seq_file *m);
>>>> - int (*map_check_btf)(const struct bpf_map *map, const struct btf *btf,
>>>> - u32 key_type_id, u32 value_type_id);
>>>> };
>>>>
>>>> struct bpf_map {
>>>> @@ -118,7 +116,7 @@ static inline bool bpf_map_offload_neutral(const struct bpf_map *map)
>>>>
>>>> static inline bool bpf_map_support_seq_show(const struct bpf_map *map)
>>>> {
>>>> - return map->ops->map_seq_show_elem && map->ops->map_check_btf;
>>>> + return map->ops->map_seq_show_elem;
>>>> }
>>>>
>>>> extern const struct bpf_map_ops bpf_map_offload_ops;
>>>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>>>> index 2aa55d030..67f0bdf 100644
>>>> --- a/kernel/bpf/arraymap.c
>>>> +++ b/kernel/bpf/arraymap.c
>>>> @@ -358,32 +358,6 @@ static void array_map_seq_show_elem(struct bpf_map *map, void *key,
>>>> rcu_read_unlock();
>>>> }
>>>>
>>>> -static int array_map_check_btf(const struct bpf_map *map, const struct btf *btf,
>>>> - u32 btf_key_id, u32 btf_value_id)
>>>> -{
>>>> - const struct btf_type *key_type, *value_type;
>>>> - u32 key_size, value_size;
>>>> - u32 int_data;
>>>> -
>>>> - key_type = btf_type_id_size(btf, &btf_key_id, &key_size);
>>>> - if (!key_type || BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
>>>> - return -EINVAL;
>>>> -
>>>> - int_data = *(u32 *)(key_type + 1);
>>>> - /* bpf array can only take a u32 key. This check makes
>>>> - * sure that the btf matches the attr used during map_create.
>>>> - */
>>>> - if (BTF_INT_BITS(int_data) != 32 || key_size != 4 ||
>>>> - BTF_INT_OFFSET(int_data))
>>>> - return -EINVAL;
>>>> -
>>>> - value_type = btf_type_id_size(btf, &btf_value_id, &value_size);
>>>> - if (!value_type || value_size != map->value_size)
>>>> - return -EINVAL;
>>>> -
>>>> - return 0;
>>>> -}
>>>> -
>>>> const struct bpf_map_ops array_map_ops = {
>>>> .map_alloc_check = array_map_alloc_check,
>>>> .map_alloc = array_map_alloc,
>>>> @@ -394,7 +368,6 @@ const struct bpf_map_ops array_map_ops = {
>>>> .map_delete_elem = array_map_delete_elem,
>>>> .map_gen_lookup = array_map_gen_lookup,
>>>> .map_seq_show_elem = array_map_seq_show_elem,
>>>> - .map_check_btf = array_map_check_btf,
>>>> };
>>>>
>>>> const struct bpf_map_ops percpu_array_map_ops = {
>>>> diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
>>>> index 76efe9a..400f27d 100644
>>>> --- a/kernel/bpf/inode.c
>>>> +++ b/kernel/bpf/inode.c
>>>> @@ -332,7 +332,8 @@ static int bpf_mkmap(struct dentry *dentry, umode_t mode, void *arg)
>>>> struct bpf_map *map = arg;
>>>>
>>>> return bpf_mkobj_ops(dentry, mode, arg, &bpf_map_iops,
>>>> - map->btf ? &bpffs_map_fops : &bpffs_obj_fops);
>>>> + bpf_map_support_seq_show(map) ?
>>>> + &bpffs_map_fops : &bpffs_obj_fops);
>>>
>>> There are an issue here, the condition bpf_map_support_seq_show(map) may not be enough since the map specific implementation assumes availability of btf and proper map key/value btf_type_id's.
>>> We can either use
>>> map->btf && bpf_map_support_seq_show(map)
>>> condition here, or check map->btf in each individual implementation
>>> of map_support_seq_show().
>>
>> Good, point, agree. Will fix and cook proper patch later today.
>
> Sounds good. i will wait until this gets merged and then resubmit.
Ok, just flushed it out. Thanks!
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