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bpf, docs: Document existing macros instead of deprecated 

The BTF_TYPE_SAFE_NESTED macro was replaced by the BTF_TYPE_SAFE_TRUSTED,
BTF_TYPE_SAFE_RCU, and BTF_TYPE_SAFE_RCU_OR_NULL macros. Fix the docs
correspondingly.

Fixes: 6fcd486b3a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20230622095424.1024244-1-aspsk@isovalent.com
This commit is contained in:
Anton Protopopov 2023-06-22 09:54:24 +00:00 committed by Daniel Borkmann
parent 2404dd01b5
commit fbc5669de6
1 changed files with 32 additions and 6 deletions
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38
Documentation/bpf/kfuncs.rst
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@ -227,23 +227,49 @@ absolutely no ABI stability guarantees.
As mentioned above, a nested pointer obtained from walking a trusted pointer is
no longer trusted, with one exception. If a struct type has a field that is
guaranteed to be valid as long as its parent pointer is trusted, the
``BTF_TYPE_SAFE_NESTED`` macro can be used to express that to the verifier as
follows:
guaranteed to be valid (trusted or rcu, as in KF_RCU description below) as long
as its parent pointer is valid, the following macros can be used to express
that to the verifier:
* ``BTF_TYPE_SAFE_TRUSTED``
* ``BTF_TYPE_SAFE_RCU``
* ``BTF_TYPE_SAFE_RCU_OR_NULL``
For example,
.. code-block:: c
BTF_TYPE_SAFE_NESTED(struct task_struct) {
BTF_TYPE_SAFE_TRUSTED(struct socket) {
struct sock *sk;
};
or
.. code-block:: c
BTF_TYPE_SAFE_RCU(struct task_struct) {
const cpumask_t *cpus_ptr;
struct css_set __rcu *cgroups;
struct task_struct __rcu *real_parent;
struct task_struct *group_leader;
};
In other words, you must:
1. Wrap the trusted pointer type in the ``BTF_TYPE_SAFE_NESTED`` macro.
1. Wrap the valid pointer type in a ``BTF_TYPE_SAFE_*`` macro.
2. Specify the type and name of the trusted nested field. This field must match
2. Specify the type and name of the valid nested field. This field must match
the field in the original type definition exactly.
A new type declared by a ``BTF_TYPE_SAFE_*`` macro also needs to be emitted so
that it appears in BTF. For example, ``BTF_TYPE_SAFE_TRUSTED(struct socket)``
is emitted in the ``type_is_trusted()`` function as follows:
.. code-block:: c
BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct socket));
2.4.5 KF_SLEEPABLE flag
-----------------------