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8b59302131
Kui-Feng Lee says:
====================
Given the current constraints of the current implementation,
struct_ops cannot be registered dynamically. This presents a
significant limitation for modules like coming fuse-bpf, which seeks
to implement a new struct_ops type. To address this issue, a new API
is introduced that allows the registration of new struct_ops types
from modules.
Previously, struct_ops types were defined in bpf_struct_ops_types.h
and collected as a static array. The new API lets callers add new
struct_ops types dynamically. The static array has been removed and
replaced by the per-btf struct_ops_tab.
The struct_ops subsystem relies on BTF to determine the layout of
values in a struct_ops map and identify the subsystem that the
struct_ops map registers to. However, the kernel BTF does not include
the type information of struct_ops types defined by a module. The
struct_ops subsystem requires knowledge of the corresponding module
for a given struct_ops map and the utilization of BTF information from
that module. We empower libbpf to determine the correct module for
accessing the BTF information and pass an identity (FD) of the module
btf to the kernel. The kernel looks up type information and registered
struct_ops types directly from the given btf.
If a module exits while one or more struct_ops maps still refer to a
struct_ops type defined by the module, it can lead to unforeseen
complications. Therefore, it is crucial to ensure that a module
remains intact as long as any struct_ops map is still linked to a
struct_ops type defined by the module. To achieve this, every
struct_ops map holds a reference to the module while being registered.
Changes from v16:
- Fix unnecessary bpf_struct_ops_link_create() removing/adding.
- Rename REGISTER_BPF_STRUCT_OPS() to register_bpf_struct_ops().
- Implement bpf_map_struct_ops_info_fill() for !CONFIG_BPF_JIT.
Changes from v15:
- Fix the misleading commit message of part 4.
- Introduce BPF_F_VTYPE_BTF_OBJ_FD flag to struct bpf_attr to tell
if value_type_btf_obj_fd is set or not.
- Introduce links_cnt to struct bpf_struct_ops_map to avoid accessing
struct bpf_struct_ops_desc in bpf_struct_ops_map_put_progs() after
calling module_put() against the owner module of the struct_ops
type. (Part 9)
Changes from v14:
- Rebase. Add cif_stub required by
the commit
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.