On Wed, Aug 13, 2025 at 1:09 PM Yureka Lilian <yuka@xxxxxxxx> 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, > but BPF_F_RDONLY_PROG being set on a map during creation is invalid. > > Thus, ignore the BPF_F_RDONLY_PROG flag on both sides when checking for > compatibility with an existing DEVMAP. > > Ignoring it on both sides ensures that it continues to work on older > kernels which don't set BPF_F_RDONLY_PROG on get_map_info. > > The same problem is handled in a third-party ebpf library: > - https://github.com/cilium/ebpf/issues/925 > - https://github.com/cilium/ebpf/pull/930 > > Fixes: 0cdbb4b09a06 ("devmap: Allow map lookups from eBPF") > Signed-off-by: Yureka Lilian <yuka@xxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index d41ee26b9..049b0c400 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -5076,6 +5076,7 @@ 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); > @@ -5088,11 +5089,22 @@ 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, ignore the BPF_F_RDONLY_PROG flag on both sides 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_info.map_flags |= BPF_F_RDONLY_PROG; > + map_flags_for_check |= BPF_F_RDONLY_PROG; > + } can we instead clear BPF_F_RDONLY_PROG in map_info.map_flags? and then keep using map->def.map_flags directly pw-bot: cr > + > 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); > } > > -- > 2.50.1 >
