In next few patches, we need a helper that searches all kernel BTFs
(vmlinux and module BTFs), and finds the type denoted by 'name' and
'kind'. Turns out bpf_btf_find_by_name_kind already does the same thing,
but it instead returns a BTF ID and optionally fd (if module BTF). This
is used for relocating ksyms in BPF loader code (bpftool gen skel -L).
We extract the core code out into a new helper
btf_find_by_name_kind_all, which returns the BTF ID and BTF pointer in
an out parameter. The reference for the returned BTF pointer is only
bumped if it is a module BTF, this needs to be kept in mind when using
this helper.
Hence, the user must release the BTF reference iff btf_is_module is
true, otherwise transfer the ownership to e.g. an fd.
In case of the helper, the fd is only allocated for module BTFs, so no
extra handling for btf_vmlinux case is required.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
kernel/bpf/btf.c | 47 +++++++++++++++++++++++++++++++----------------
1 file changed, 31 insertions(+), 16 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 2c4c5dbe2abe..3645d8c14a18 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6545,16 +6545,10 @@ static struct btf *btf_get_module_btf(const struct module *module)
return btf;
}
-BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
+static s32 btf_find_by_name_kind_all(const char *name, u32 kind, struct btf **btfp)
{
struct btf *btf;
- long ret;
-
- if (flags)
- return -EINVAL;
-
- if (name_sz <= 1 || name[name_sz - 1])
- return -EINVAL;
+ s32 ret;
btf = bpf_get_btf_vmlinux();
if (IS_ERR(btf))
@@ -6580,19 +6574,40 @@ BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int
spin_unlock_bh(&btf_idr_lock);
ret = btf_find_by_name_kind(mod_btf, name, kind);
if (ret > 0) {
- int btf_obj_fd;
-
- btf_obj_fd = __btf_new_fd(mod_btf);
- if (btf_obj_fd < 0) {
- btf_put(mod_btf);
- return btf_obj_fd;
- }
- return ret | (((u64)btf_obj_fd) << 32);
+ *btfp = mod_btf;
+ return ret;
}
spin_lock_bh(&btf_idr_lock);
btf_put(mod_btf);
}
spin_unlock_bh(&btf_idr_lock);
+ } else {
+ *btfp = btf;
+ }
+ return ret;
+}
+
+BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
+{
+ struct btf *btf = NULL;
+ int btf_obj_fd = 0;
+ long ret;
+
+ if (flags)
+ return -EINVAL;
+
+ if (name_sz <= 1 || name[name_sz - 1])
+ return -EINVAL;
+
+ ret = btf_find_by_name_kind_all(name, kind, &btf);
+ if (ret > 0 && btf_is_module(btf)) {
+ /* reference for btf is only raised if module BTF */
+ btf_obj_fd = __btf_new_fd(btf);
+ if (btf_obj_fd < 0) {
+ btf_put(btf);
+ return btf_obj_fd;
+ }
+ return ret | (((u64)btf_obj_fd) << 32);
}
return ret;
}
--
2.35.1
