On 23-Jan 12:06, Andrii Nakryiko wrote:

On Thu, Jan 23, 2020 at 7:25 AM KP Singh [off-list ref] wrote:

quoted

From: KP Singh <redacted>

- The LSM code does the combination of btf_find_by_name_kind and
  btf_type_by_id a couple of times to figure out the BTF type for
  security_hook_heads and security_list_options.
- Add an extern for btf_vmlinux in btf.h

Signed-off-by: KP Singh <redacted>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Florent Revest <redacted>
Reviewed-by: Thomas Garnier <redacted>
---
 include/linux/btf.h |  3 +++
 kernel/bpf/btf.c    | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 5c1ea99b480f..d4e859f90a39 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h

@@ -15,6 +15,7 @@ struct btf_type;
 union bpf_attr;

 extern const struct file_operations btf_fops;
+extern struct btf *btf_vmlinux;

 void btf_put(struct btf *btf);
 int btf_new_fd(const union bpf_attr *attr);

@@ -66,6 +67,8 @@ const struct btf_type *
 btf_resolve_size(const struct btf *btf, const struct btf_type *type,
                 u32 *type_size, const struct btf_type **elem_type,
                 u32 *total_nelems);
+const struct btf_type *btf_type_by_name_kind(
+       struct btf *btf, const char *name, u8 kind);

 #define for_each_member(i, struct_type, member)                        \
        for (i = 0, member = btf_type_member(struct_type);      \

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 32963b6d5a9c..ea53c16802cb 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c

@@ -441,6 +441,18 @@ const struct btf_type *btf_type_resolve_func_ptr(const struct btf *btf,
        return NULL;
 }

+const struct btf_type *btf_type_by_name_kind(
+       struct btf *btf, const char *name, u8 kind)
+{
+       s32 type_id;
+
+       type_id = btf_find_by_name_kind(btf, name, kind);
+       if (type_id < 0)
+               return ERR_PTR(type_id);
+
+       return btf_type_by_id(btf, type_id);
+}
+

is it worth having this as a separate global function? If
btf_find_by_name_kind returns valid ID, then you don't really need to
check btf_type_by_id result, it is always going to be valid. So the
pattern becomes:

Yeah you're right. We went from using this a few times in separate
functions to 2 times in the same function (based on the changes in
v2 -> v3)

I will drop this from the next revision.

 

type_id = btf_find_by_name_kind(btf, name, kind);
if (type_id < 0)
  goto handle_error;
t = btf_type_by_id(btf, type_id);
/* now just use t */

which is not much more verbose than:

t = btf_type_by_name_kind(btf, name, kind);
if (IS_ERR(t))
  goto handle_error
/* now use t */

Agreed.

- KP

quoted

 /* Types that act only as a source, not sink or intermediate
  * type when resolving.
  */
--
2.20.1