docs/bpf: Add bpf() syscall command reference

Generate the syscall command reference from the UAPI header file and
include it in the main bpf docs page.

Signed-off-by: Joe Stringer <joe@cilium.io>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210302171947.2268128-15-joe@cilium.io

Documentation/bpf/index.rst

@@ -12,9 +12,6 @@ BPF instruction-set.
 The Cilium project also maintains a `BPF and XDP Reference Guide`_
 that goes into great technical depth about the BPF Architecture.
 
-The primary info for the bpf syscall is available in the `man-pages`_
-for `bpf(2)`_.
-
 BPF Type Format (BTF)
 =====================
 
@@ -35,6 +32,12 @@ Two sets of Questions and Answers (Q&A) are maintained.
    bpf_design_QA
    bpf_devel_QA
 
+Syscall API
+===========
+
+The primary info for the bpf syscall is available in the `man-pages`_
+for `bpf(2)`_. For more information about the userspace API, see
+Documentation/userspace-api/ebpf/index.rst.
 
 Helper functions
 ================

Documentation/userspace-api/ebpf/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+eBPF Userspace API
+==================
+
+eBPF is a kernel mechanism to provide a sandboxed runtime environment in the
+Linux kernel for runtime extension and instrumentation without changing kernel
+source code or loading kernel modules. eBPF programs can be attached to various
+kernel subsystems, including networking, tracing and Linux security modules
+(LSM).
+
+For internal kernel documentation on eBPF, see Documentation/bpf/index.rst.
+
+.. toctree::
+   :maxdepth: 1
+
+   syscall

Documentation/userspace-api/ebpf/syscall.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+eBPF Syscall
+------------
+
+:Authors: - Alexei Starovoitov <ast@kernel.org>
+          - Joe Stringer <joe@wand.net.nz>
+          - Michael Kerrisk <mtk.manpages@gmail.com>
+
+The primary info for the bpf syscall is available in the `man-pages`_
+for `bpf(2)`_.
+
+bpf() subcommand reference
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/uapi/linux/bpf.h
+   :doc: eBPF Syscall Preamble
+
+.. kernel-doc:: include/uapi/linux/bpf.h
+   :doc: eBPF Syscall Commands
+
+.. Links:
+.. _man-pages: https://www.kernel.org/doc/man-pages/
+.. _bpf(2): https://man7.org/linux/man-pages/man2/bpf.2.html

Documentation/userspace-api/index.rst

@@ -21,6 +21,7 @@ place where this information is gathered.
    unshare
    spec_ctrl
    accelerators/ocxl
+   ebpf/index
    ioctl/index
    iommu
    media/index

MAINTAINERS

@@ -3209,6 +3209,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
 F:	Documentation/bpf/
 F:	Documentation/networking/filter.rst
+F:	Documentation/userspace-api/ebpf/
 F:	arch/*/net/*
 F:	include/linux/bpf*
 F:	include/linux/filter.h