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libbpf: Skip zeroed or null fields if not found in the kernel type.

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Accept additional fields of a struct_ops type with all zero values even if
these fields are not in the corresponding type in the kernel. This provides
a way to be backward compatible. User space programs can use the same map
on a machine running an old kernel by clearing fields that do not exist in
the kernel.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240313214139.685112-2-thinker.li@gmail.com
This commit is contained in:
Kui-Feng Lee 2024-03-13 14:41:37 -07:00 committed by Andrii Nakryiko
parent 9bf48fa19a
commit c911fc61a7
1 changed files with 19 additions and 5 deletions
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24
tools/lib/bpf/libbpf.c
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@ -1132,8 +1132,26 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
const char *mname;
mname = btf__name_by_offset(btf, member->name_off);
moff = member->offset / 8;
mdata = data + moff;
msize = btf__resolve_size(btf, member->type);
if (msize < 0) {
pr_warn("struct_ops init_kern %s: failed to resolve the size of member %s\n",
map->name, mname);
return msize;
}
kern_member = find_member_by_name(kern_btf, kern_type, mname);
if (!kern_member) {
/* Skip all zeros or null fields if they are not
* presented in the kernel BTF.
*/
if (libbpf_is_mem_zeroed(mdata, msize)) {
pr_info("struct_ops %s: member %s not found in kernel, skipping it as it's set to zero\n",
map->name, mname);
continue;
}
pr_warn("struct_ops init_kern %s: Cannot find member %s in kernel BTF\n",
map->name, mname);
return -ENOTSUP;
@ -1147,10 +1165,7 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
return -ENOTSUP;
}
moff = member->offset / 8;
kern_moff = kern_member->offset / 8;
mdata = data + moff;
kern_mdata = kern_data + kern_moff;
mtype = skip_mods_and_typedefs(btf, member->type, &mtype_id);
@ -1230,9 +1245,8 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
continue;
}
msize = btf__resolve_size(btf, mtype_id);
kern_msize = btf__resolve_size(kern_btf, kern_mtype_id);
if (msize < 0 || kern_msize < 0 || msize != kern_msize) {
if (kern_msize < 0 || msize != kern_msize) {
pr_warn("struct_ops init_kern %s: Error in size of member %s: %zd != %zd(kernel)\n",
map->name, mname, (ssize_t)msize,
(ssize_t)kern_msize);