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 <y...@fb.com>
Acked-by: Alexei Starovoitov <a...@kernel.org>
