Re: [PATCH v5 bpf-next 3/4] bpf: Add kernel module with user mode driver that populates bpffs.

[Daniel Borkmann <daniel@iogearbox.net>]

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@kernel.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@kernel.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?
> 
> 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@tank:~/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
  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@tank:~/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)
                      ^~~~~~~~~~~~
In file included from kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.c:16:0:
/usr/include/stdlib.h:558:14: note: previous declaration of ‘reallocarray’ was here
  extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
               ^~~~~~~~~~~~
   CC      kernel/user-return-notifier.o
scripts/Makefile.userprogs:43: recipe for target 'kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o' failed
make[3]: *** [kernel/bpf/preload/./../../../tools/lib/bpf/libbpf.o] Error 1
scripts/Makefile.build:497: recipe for target 'kernel/bpf/preload' failed
make[2]: *** [kernel/bpf/preload] Error 2
scripts/Makefile.build:497: recipe for target 'kernel/bpf' failed
make[1]: *** [kernel/bpf] Error 2
make[1]: *** Waiting for unfinished jobs....
[...]