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.
>
> So this patch probably should apply to bpf-next or
> I can include this patch in my later patch set
> which implements map_seq_show_elem for hash map
> which can demonstrate the problem.
>
> Please let me know.
>
>>> Fixes: a26ca7c982cb5 ("bpf: btf: Add pretty print support to the basic
>>> arraymap")
>>> Signed-off-by: Yonghong Song <[email protected]>
>>
>> Acked-by: Alexei Starovoitov <[email protected]>
Given this doesn't affect any current code, I think bpf-next
would be fine.
Anyway, this cannot be used as-is, results in following compile
warning ...
# make -j4 kernel/bpf/
DESCEND objtool
CALL scripts/checksyscalls.sh
CC kernel/bpf/verifier.o
CC kernel/bpf/inode.o
kernel/bpf/inode.c: In function ‘map_seq_next’:
kernel/bpf/inode.c:214:1: warning: label ‘done’ defined but not used
[-Wunused-label]
done:
^~~~
AR kernel/bpf/built-in.a
