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Date:   Mon, 3 Aug 2020 11:33:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 3/4] bpf: Add kernel module with user mode
 driver that populates bpffs.

On Mon, Aug 3, 2020 at 10:40 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 8/3/20 7:34 PM, Daniel Borkmann wrote:
> > On 8/3/20 7:15 PM, Daniel Borkmann wrote:
> >> On 8/3/20 12:29 AM, Alexei Starovoitov wrote:
> >>> From: Alexei Starovoitov <ast@...nel.org>
> >>>
> >>> Add kernel module with user mode driver that populates bpffs with
> >>> BPF iterators.
> >>>
> >>> $ mount bpffs /my/bpffs/ -t bpf
> >>> $ ls -la /my/bpffs/
> >>> total 4
> >>> drwxrwxrwt  2 root root    0 Jul  2 00:27 .
> >>> drwxr-xr-x 19 root root 4096 Jul  2 00:09 ..
> >>> -rw-------  1 root root    0 Jul  2 00:27 maps.debug
> >>> -rw-------  1 root root    0 Jul  2 00:27 progs.debug
> >>>
> >>> The user mode driver will load BPF Type Formats, create BPF maps, populate BPF
> >>> maps, load two BPF programs, attach them to BPF iterators, and finally send two
> >>> bpf_link IDs back to the kernel.
> >>> The kernel will pin two bpf_links into newly mounted bpffs instance under
> >>> names "progs.debug" and "maps.debug". These two files become human readable.
> >>>
> >>> $ cat /my/bpffs/progs.debug
> >>>    id name            attached
> >>>    11 dump_bpf_map    bpf_iter_bpf_map
> >>>    12 dump_bpf_prog   bpf_iter_bpf_prog
> >>>    27 test_pkt_access
> >>>    32 test_main       test_pkt_access test_pkt_access
> >>>    33 test_subprog1   test_pkt_access_subprog1 test_pkt_access
> >>>    34 test_subprog2   test_pkt_access_subprog2 test_pkt_access
> >>>    35 test_subprog3   test_pkt_access_subprog3 test_pkt_access
> >>>    36 new_get_skb_len get_skb_len test_pkt_access
> >>>    37 new_get_skb_ifindex get_skb_ifindex test_pkt_access
> >>>    38 new_get_constant get_constant test_pkt_access
> >>>
> >>> The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about
> >>> all BPF programs currently loaded in the system. This information is unstable
> >>> and will change from kernel to kernel as ".debug" suffix conveys.
> >>>
> >>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> >> [...]
> >>> diff --git a/kernel/bpf/preload/Kconfig b/kernel/bpf/preload/Kconfig
> >>> new file mode 100644
> >>> index 000000000000..b8ba5a9398ed
> >>> --- /dev/null
> >>> +++ b/kernel/bpf/preload/Kconfig
> >>> @@ -0,0 +1,18 @@
> >>> +# SPDX-License-Identifier: GPL-2.0-only
> >>> +menuconfig BPF_PRELOAD
> >>> +    bool "Preload BPF file system with kernel specific program and map iterators"
> >>> +    depends on BPF
> >>> +    help
> >>> +      This builds kernel module with several embedded BPF programs that are
> >>> +      pinned into BPF FS mount point as human readable files that are
> >>> +      useful in debugging and introspection of BPF programs and maps.
> >>> +
> >>> +if BPF_PRELOAD
> >>> +config BPF_PRELOAD_UMD
> >>> +    tristate "bpf_preload kernel module with user mode driver"
> >>> +    depends on CC_CAN_LINK
> >>> +    depends on m || CC_CAN_LINK_STATIC
> >>> +    default m
> >>> +    help
> >>> +      This builds bpf_preload kernel module with embedded user mode driver.
> >>> +endif
> >> [...]
> >> When I applied this set locally to run build & selftests I noticed that the above
> >> kconfig will appear in the top-level menuconfig. This is how it looks in menuconfig:
> >>
> >>    │ ┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ │
> >>    │ │                                           General setup  --->                                                                                      │ │
> >>    │ │                                       [*] 64-bit kernel                                                                                            │ │
> >>    │ │                                           Processor type and features  --->                                                                        │ │
> >>    │ │                                           Power management and ACPI options  --->                                                                  │ │
> >>    │ │                                           Bus options (PCI etc.)  --->                                                                             │ │
> >>    │ │                                           Binary Emulations  --->                                                                                  │ │
> >>    │ │                                           Firmware Drivers  --->                                                                                   │ │
> >>    │ │                                       [*] Virtualization  --->                                                                                     │ │
> >>    │ │                                           General architecture-dependent options  --->                                                             │ │
> >>    │ │                                       [*] Enable loadable module support  --->                                                                     │ │
> >>    │ │                                       -*- Enable the block layer  --->                                                                             │ │
> >>    │ │                                           IO Schedulers  --->                                                                                      │ │
> >>    │ │                                       [ ] Preload BPF file system with kernel specific program and map iterators  ----                             │ │
> >>    │ │                                           Executable file formats  --->                                                                            │ │
> >>    │ │                                           Memory Management options  --->                                                                          │ │
> >>    │ │                                       [*] Networking support  --->                                                                                 │ │
> >>    │ │                                           Device Drivers  --->                                                                                     │ │
> >>    │ │                                           File systems  --->                                                                                       │ │
> >>    │ │                                           Security options  --->                                                                                   │ │
> >> [...]
> >>
> >> I assume the original intention was to have it under 'general setup' on a similar level for
> >> the JIT settings, or is this intentional to have it at this high level next to 'networking
> >> support' and others?

I don't remember when last time I did menuconfig.
How do you propose to move it?
Any particular suggestion how kconfig suppose to look like?

> >
> > Hm, my config has:
> >
> > CONFIG_BPF_PRELOAD=y
> > CONFIG_BPF_PRELOAD_UMD=y
> >
> > I'm getting the following 3 warnings and build error below:
> >
> > root@...k:~/bpf-next# make -j8 > /dev/null
> > arch/x86/hyperv/hv_apic.c: In function ‘hv_send_ipi_mask_allbutself’:
> > arch/x86/hyperv/hv_apic.c:236:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> >   }
> >   ^
> > make[3]: *** No rule to make target 'kernel/bpf/preload/./../../tools/lib/bpf/bpf.c', needed by 'kernel/bpf/preload/./../../tools/lib/bpf/bpf.o'.  Stop.
> > make[3]: *** Waiting for unfinished jobs....
> > kernel/bpf/preload/iterators/iterators.c: In function ‘main’:
> > kernel/bpf/preload/iterators/iterators.c:50:2: warning: ignoring return value of ‘dup’, declared with attribute warn_unused_result [-Wunused-result]
> >    dup(debug_fd);
> >    ^~~~~~~~~~~~~
> > kernel/bpf/preload/iterators/iterators.c:53:2: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
> >    read(from_kernel, &magic, sizeof(magic));
> >    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > kernel/bpf/preload/iterators/iterators.c:85:2: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
> >    read(from_kernel, &magic, sizeof(magic));
> >    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > make[2]: *** [kernel/bpf/preload] Error 2
> > make[1]: *** [kernel/bpf] Error 2
> > make: *** [kernel] Error 2
> > make: *** Waiting for unfinished jobs....
> > [...]
> >
> > Have you seen the target error before, what am I missing?
>
> Looks like the path in this patch is wrong:
>
> diff --git a/kernel/bpf/preload/Makefile b/kernel/bpf/preload/Makefile
> index 191d82209842..136c6ca0c196 100644
> --- a/kernel/bpf/preload/Makefile
> +++ b/kernel/bpf/preload/Makefile
> @@ -1,6 +1,6 @@
>   # SPDX-License-Identifier: GPL-2.0
>
> -LIBBPF := $(srctree)/../../tools/lib/bpf
> +LIBBPF := $(srctree)/../../../tools/lib/bpf

hmm. that's very odd.
Are you building in-src-tree ?
I'm building out-of-src-tree with KBUILD_OUTPUT.
And two pairs of dots would be correct.
make V=1 kernel/bpf/preload/
gcc  -m64 -lelf -lz  -o kernel/bpf/preload/bpf_preload_umd
kernel/bpf/preload/iterators/iterators.o
kernel/bpf/preload/../../../tools/lib/bpf/bpf.o

see three pairs above. the first pair comes from $(srctree) somehow.

>   userccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi -I $(LIBBPF) \
>          -I $(srctree)/tools/lib/ \
>          -I $(srctree)/kernel/bpf/preload/iterators/ -Wno-int-conversion \
>
> With that, I'm now getting the following error:
>
> root@...k:~/bpf-next# make -j8
>    DESCEND  objtool
>    DESCEND  bpf/resolve_btfids
>    CALL    scripts/atomic/check-atomics.sh
>    CALL    scripts/checksyscalls.sh
>    CHK     include/generated/compile.h
>    CC      kernel/events/core.o
>    CC [U]  kernel/bpf/preload/iterators/iterators.o
> kernel/bpf/preload/iterators/iterators.c: In function ‘main’:
> kernel/bpf/preload/iterators/iterators.c:50:2: warning: ignoring return value of ‘dup’, declared with attribute warn_unused_result [-Wunused-result]
>    dup(debug_fd);
>    ^~~~~~~~~~~~~
> kernel/bpf/preload/iterators/iterators.c:53:2: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
>    read(from_kernel, &magic, sizeof(magic));
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> kernel/bpf/preload/iterators/iterators.c:85:2: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
>    read(from_kernel, &magic, sizeof(magic));
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    CC      kernel/events/ring_buffer.o
>    CC [U]  kernel/bpf/preload/./../../../tools/lib/bpf/bpf.o
>    CC [U]  kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o
> In file included from kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.c:47:0:
> ./tools/include/tools/libc_compat.h:11:21: error: static declaration of ‘reallocarray’ follows non-static declaration
>   static inline void *reallocarray(void *ptr, size_t nmemb, size_t size)
>                       ^~~~~~~~~~~~

I saw this in the past when makefile was wrong. I suspect it's related
to the above issue.
Could you send me your build script / command line and make version?

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