On 8/11/25 2:39 AM, Yureka Lilian wrote:
Previously, re-using pinned DEVMAP maps would always fail, because
get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set,
it BPF_F_RDONLY_PROG being set on a map being created is invalid.
Thus, match the BPF_F_RDONLY_PROG flag being set on the new map when
checking for compatibility with an existing DEVMAP
The same problem is handled in third-party ebpf library:
- https://github.com/cilium/ebpf/issues/925
- https://github.com/cilium/ebpf/pull/930
Signed-off-by: Yureka Lilian <yuka@xxxxxxxx>
This should be a fix for this commit?
Fixes: 0cdbb4b09a06 ("devmap: Allow map lookups from eBPF")
---
tools/lib/bpf/libbpf.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fb4d92c5c..a554d7fff 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5081,6 +5081,7 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
{
struct bpf_map_info map_info;
__u32 map_info_len = sizeof(map_info);
+ __u32 map_flags_for_check = map->def.map_flags;
int err;
memset(&map_info, 0, map_info_len);
@@ -5093,11 +5094,20 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
return false;
}
+ /* get_map_info on a DEVMAP will always return flags with
+ * BPF_F_RDONLY_PROG set, but it will never be set on a map
+ * being created.
+ * Thus, match the BPF_F_RDONLY_PROG flag being set on the new
+ * map when checking for compatibility with an existing DEVMAP
+ */
+ if (map->def.type == BPF_MAP_TYPE_DEVMAP || map->def.type == BPF_MAP_TYPE_DEVMAP_HASH)
+ map_flags_for_check |= BPF_F_RDONLY_PROG;
Does it break older kernels that do not set the RDONLY_PROG bit implicitly by
itself?
+
return (map_info.type == map->def.type &&
map_info.key_size == map->def.key_size &&
map_info.value_size == map->def.value_size &&
map_info.max_entries == map->def.max_entries &&
- map_info.map_flags == map->def.map_flags &&
+ map_info.map_flags == map_flags_for_check &&
map_info.map_extra == map->map_extra);
}
