linux-kernel - Re: [PATCH 04/16] bpf tools: Collect map definition in bpf

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Message-ID: <5657F669.5070404@huawei.com>
Date:	Fri, 27 Nov 2015 14:21:29 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	<masami.hiramatsu.pt@...achi.com>, <ast@...nel.org>,
	<lizefan@...wei.com>, <pi3orama@....com>,
	<linux-kernel@...r.kernel.org>, Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 04/16] bpf tools: Collect map definition in bpf_object



On 2015/11/27 14:16, Wangnan (F) wrote:
>
>
> On 2015/11/27 4:56, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Nov 24, 2015 at 01:36:09PM +0000, Wang Nan escreveu:
>
> [SNIP]

[SNIP]

>>> +
>>> +    if ((prev < s) || (prev >= e)) {
>>> +        pr_warning("error: map handler doesn't belong to object\n");
>> I wonder if this shouldn't be made pr_debug, and as well have a function
>> prefix, otherwise we may think this is related to some other kind of
>> map, so I suggest:
>>         pr_debug("%s: error: map handler doesn't belong to object\n", 
>> __func__);
>>
>> Or at least:
>>
>>         pr_debug("BPF error: map handler doesn't belong to object\n");
>
> We always have a libbpf prefix before debug info from libbpf. Please see
>
> static __printf(1, 2) libbpf_print_fn_t __pr_warning = __base_pr;
> static __printf(1, 2) libbpf_print_fn_t __pr_info = __base_pr;
> static __printf(1, 2) libbpf_print_fn_t __pr_debug;
> #define __pr(func, fmt, ...)    \
> do {                            \
>         if ((func))             \
>                 (func)("libbpf: " fmt, ##__VA_ARGS__); \
> } while (0)
>
> #define pr_warning(fmt, ...)    __pr(__pr_warning, fmt, ##__VA_ARGS__)
> #define pr_info(fmt, ...)       __pr(__pr_info, fmt, ##__VA_ARGS__)
> #define pr_debug(fmt, ...)      __pr(__pr_debug, fmt, ##__VA_ARGS__)
>
> We allow __pr_{warning,info,debug} be overwritten but the 'libbpf:' 
> prefix is
> always there.
>
> Also, don't forget in perf's context libbpf is muted.
>
Sorry, Shoule be "muted in most case"...

Here's an example:

$ sudo ./perf record -v -e ./test_bpf_base.c ls
...
ude/uapi -Iinclude/generated/uapi -include 
/home/w00229757/linux-hydrogen/include/linux/kconfig.h
set env: WORKING_DIR=/lib/modules/4.3.0-rc4+/build
set env: CLANG_SOURCE=/home/w00229757/./test_bpf_base.c
llvm compiling command template: $CLANG_EXEC -D__KERNEL__ 
-D__NR_CPUS__=$NR_CPUS -DLINUX_VERSION_CODE=$LINUX_VERSION_CODE 
$CLANG_OPTIONS $KERNEL_INC_OPTIONS -Wno-unused-value -Wno-pointer-sign 
-working-directory $WORKING_DIR -c "$CLANG_SOURCE" -target bpf -O2 -o -
libbpf: loading object './test_bpf_base.c' from buffer
libbpf: section .strtab, size 112, link 0, flags 0, type=3
libbpf: section .text, size 0, link 0, flags 6, type=1
libbpf: section .data, size 0, link 0, flags 3, type=1
...
libbpf: kernel version of ./test_bpf_base.c is 40300
libbpf: section .symtab, size 96, link 1, flags 0, type=2
bpf: config program 'func_write=vfs_write file->f_mode'
symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
parsing arg: file->f_mode into file, f_mode(1)
bpf: config 'func_write=vfs_write file->f_mode' is ok

If the error you pointed out is triggered, it should be:

libbpf: error: map handler doesn't belong to object ...

So we can always find which error message is belone to libbpf
and which is belone to perf.

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