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libbpf: Fix reuse of DEVMAP

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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 in the flags returned from
get_map_info when checking for compatibility with an existing DEVMAP.

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@yuka.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250814180113.1245565-3-yuka@yuka.dev
This commit is contained in:
Yureka Lilian
2025-08-14 20:01:12 +02:00
committed by Andrii Nakryiko
parent fc687b8ee9
commit 04a23358c7
1 changed files with 10 additions and 0 deletions
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10
src/libbpf.c
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@@ -5093,6 +5093,16 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
return false;
}
/*
* bpf_get_map_info_by_fd() for DEVMAP will always return flags with
* BPF_F_RDONLY_PROG set, but it generally is not set at map creation time.
* Thus, ignore the BPF_F_RDONLY_PROG flag in the flags returned from
* bpf_get_map_info_by_fd() 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;
return (map_info.type == map->def.type &&
map_info.key_size == map->def.key_size &&
map_info.value_size == map->def.value_size &&