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David Vernet says: ==================== The struct bpf_struct_ops structure in BPF is a framework that allows subsystems to extend themselves using BPF. In commit68b04864ca("bpf: Create links for BPF struct_ops maps") and commitaef56f2e91("bpf: Update the struct_ops of a bpf_link"), the structure was updated to include new ->validate() and ->update() callbacks respectively in support of allowing struct_ops maps to be created with BPF_F_LINK. The intention was that struct bpf_struct_ops implementations could support map updates through the link. Because map validation and registration would take place in two separate steps for struct_ops maps managed by the link (the first in map update elem, and the latter in link create), the ->validate() callback was added, and any struct_ops implementation that wished to use BPF_F_LINK, even just for lifetime management, would then be required to define both it and ->update(). Not all struct_ops implementations can or will support update, however. For example, the sched_ext struct_ops implementation proposed in [0] will not be able to support atomic map updates because it can race with sysrq, has to cycle tasks through various states in order to safely transition, etc. It can, however, benefit from letting the BPF link automatically evict the struc_ops map when the application exits (e.g. if it crashes). This patch set therefore: 1. Updates the struct_ops implementation to support default values for ->validate() and ->update() so that struct_ops implementations can benefit from BPF_F_LINK management even if they can't support updates. 2. Documents struct bpf_struct_ops so that the semantics are clear and well defined. --- v2: https://lore.kernel.org/bpf/0f5ea3de-c6e7-490f-b5ec-b5c7cd288687@gmail.com/T/ Changes from v2 -> v3: - Add patch 2/2 that documents the struct bpf_struct_ops structure. - Add Kui-Feng's Acked-by tag to patch 1/2. v1: https://lore.kernel.org/lkml/20230811150934.GA542801@maniforge/ Changes from v1 -> v2: - Move the if (!st_map->st_ops->update) check outside of the critical section before we acquire the update_mutex. ==================== Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
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.