5ca7867078
struct cgroup * objects have a variably sized struct cgroup *ancestors[] field which stores pointers to their ancestor cgroups. If using a cgroup as a kptr, it can be useful to access these ancestors, but doing so requires variable offset accesses for PTR_TO_BTF_ID, which is currently unsupported. This is a very useful field to access for cgroup kptrs, as programs may wish to walk their ancestor cgroups when determining e.g. their proportional cpu.weight. So as to enable this functionality with cgroup kptrs before var_off is supported for PTR_TO_BTF_ID, this patch adds a bpf_cgroup_ancestor() kfunc which accesses the cgroup node on behalf of the caller, and acquires a reference on it. Once var_off is supported for PTR_TO_BTF_ID, and fields inside a struct can be marked as trusted so they retain the PTR_TRUSTED modifier when walked, this can be removed. Signed-off-by: David Vernet <void@manifault.com> Link: https://lore.kernel.org/r/20221122055458.173143-4-void@manifault.com 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.