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David Vernet says: ==================== A series of recent patch sets introduced kfuncs that allowed struct task_struct and struct cgroup objects to be used as kptrs. These were introduced in [0], [1], and [2]. [0]: https://lore.kernel.org/lkml/20221120051004.3605026-1-void@manifault.com/ [1]: https://lore.kernel.org/lkml/20221122145300.251210-2-void@manifault.com/T/ [2]: https://lore.kernel.org/lkml/20221122055458.173143-1-void@manifault.com/ These are "core" kfuncs, in that they may be used by a wide variety of possible BPF tracepoint or struct_ops programs, and are defined in kernel/bpf/helpers.c. Even though as kfuncs they have no ABI stability guarantees, they should still be properly documented. This patch set adds that documentation. Some other kfuncs were added recently as well, such as bpf_rcu_read_lock() and bpf_rcu_read_unlock(). Those could and should be added to this "Core kfuncs" section as well in subsequent patch sets. Note that this patch set does not contain documentation for bpf_task_acquire_not_zero(), or bpf_task_kptr_get(). As discussed in [3], those kfuncs currently always return NULL pending resolution on how to properly protect their arguments using RCU. [3]: https://lore.kernel.org/all/20221206210538.597606-1-void@manifault.com/ --- Changelog: v2 -> v3: - Don't document bpf_task_kptr_get(), and instead provide a more substantive example for bpf_cgroup_kptr_get(). - Further clarify expected behavior of bpf_task_from_pid() in comments (Alexei) v1 -> v2: - Expand comment to specify that a map holds a reference to a task kptr if we don't end up releasing it (Alexei) - Just read task->pid instead of using a probed read (Alexei) ==================== Signed-off-by: Alexei Starovoitov <ast@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.