On Wed, Mar 11, 2020 at 12:14:40PM -0700, Andrey Ignatov wrote: > It's a follow-up for discussion in [1]. > > drgn tool bpf_inspect.py was merged to drgn repo in [2]. Document it in > kernel tree to make BPF developers aware that the tool exists and can > help with getting BPF state unavailable via UAPI. > > For now it's just one tool but the doc is written in a way that allows > to cover more tools in the future if needed. > > Please refer to the doc itself for more details. > > The patch was tested by `make htmldocs` and sanity-checking that > resulting html looks good. > > [1] > https://lore.kernel.org/bpf/20200228201514.GB51456@rdna-mbp/T/#mefed65e8a98116bd5d07d09a570a3eac46724951 > [2] https://github.com/osandov/drgn/pull/49 > > Signed-off-by: Andrey Ignatov <rdna@xxxxxx> > --- > Documentation/bpf/drgn.rst | 42 +++++++++++++++++++++++++++++++++++++ > Documentation/bpf/index.rst | 5 +++-- > 2 files changed, 45 insertions(+), 2 deletions(-) > create mode 100644 Documentation/bpf/drgn.rst Location looks good, but I gotta nit pick on wording... > diff --git a/Documentation/bpf/drgn.rst b/Documentation/bpf/drgn.rst > new file mode 100644 > index 000000000000..9a9ad75ab066 > --- /dev/null > +++ b/Documentation/bpf/drgn.rst > @@ -0,0 +1,42 @@ > +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) > + > +============== > +BPF drgn tools > +============== > + > +drgn scripts are great to debug kernel internals including BPF and get > +information unavailable via conventional kernel UAPI. > + > +If there is a piece of kernel state useful for a small number of users, e.g. > +only for BPF developers, or too expensive to expose to user space, drgn script > +can be a good option to still have access to that state but without extending > +UAPI. Above two paragraphs are true for any piece of kernel data. I think they're unnecessary focusing attention on bpf. May be rephrase the whole thing like: " drgn scripts is a convenient and easy to use mechanism to retrieve arbitrary kernel data structures. drgn is not relying on kernel UAPI to read the data. Instead it's reading directly from /proc/kcore or vmcore and pretty prints the data based on dwarf debug information from vmlinux. " > + > +This document describes BPF related drgn tools. > + > +See `drgn/tools`_ for all tools available at the moment and `drgn/doc`_ for > +more details on drgn itself. > + > +bpf_inspect.py > +************** > + > +`bpf_inspect.py`_ is a tool intended to inspect BPF programs and maps. It can > +iterate over all programs and maps in the system and print basic information > +about these objects, including id, type and name. > + > +The main use-case `bpf_inspect.py`_ covers is to show BPF programs of types > +``BPF_PROG_TYPE_EXT`` and ``BPF_PROG_TYPE_TRACING`` attached to other BPF > +programs via ``freplace``/``fentry``/``fexit`` mechanisms, since there is no > +user-space API to get this information. > + > +But developer can edit the tool and get any piece of ``struct bpf_prog`` or Just drop 'but' and say 'Any developer can edit ...' > +``struct bpf_map`` they're interested in, e.g. the whole ``struct > +bpf_prog_aux``. > +
