When a BPF-map type doesn't support having a BTF info associated, the
bpf_map_ops->map_check_btf is set to map_check_no_btf(). This function
map_check_no_btf() currently returns -ENOTSUPP, which result in a very
confusing error message in libbpf, see below.
The errno ENOTSUPP is part of the kernels internal errno in file
include/linux/errno.h. As is stated in the file, these "should never be
seen by user programs". This is not a not a standard Unix error.
This should likely have been EOPNOTSUPP instead. This seems to be a common
mistake, that even checkpatch tries to catch see commit 6b9ea5ff5abd
("checkpatch: warn about uses of ENOTSUPP").
Before this change end-users of libbpf will see:
libbpf: Error in bpf_create_map_xattr(cpu_map):ERROR: strerror_r(-524)=22(-524). Retrying without BTF.
After this change end-users of libbpf will see:
libbpf: Error in bpf_create_map_xattr(cpu_map):Operation not supported(-95). Retrying without BTF.
V2: Use EOPNOTSUPP instead of EUCLEAN.
Fixes: e8d2bec04579 ("bpf: decouple btf from seq bpf fs dump and enable more maps")
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
kernel/bpf/syscall.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index d13b804ff045..e4e0a0c5192c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -732,7 +732,7 @@ int map_check_no_btf(const struct bpf_map *map,
const struct btf_type *key_type,
const struct btf_type *value_type)
{
- return -ENOTSUPP;
+ return -EOPNOTSUPP;
}
static int map_check_btf(struct bpf_map *map, const struct btf *btf,
