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From: Joe Perches <joe@perches.com>
To: Alan Maguire <alan.maguire@oracle.com>,
	ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org
Cc: linux@rasmusvillemoes.dk, arnaldo.melo@gmail.com, yhs@fb.com,
	kafai@fb.com, songliubraving@fb.com, andriin@fb.com,
	john.fastabend@gmail.com, kpsingh@chromium.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH v2 bpf-next 4/7] printk: add type-printing %pT format specifier which uses BTF
Date: Wed, 13 May 2020 16:05:41 -0700	[thread overview]
Message-ID: <1b63a6b193073674b6e0f9f95c62ce2af1b977cc.camel@perches.com> (raw)
In-Reply-To: <1589263005-7887-5-git-send-email-alan.maguire@oracle.com>

On Tue, 2020-05-12 at 06:56 +0100, Alan Maguire wrote:
> printk supports multiple pointer object type specifiers (printing
> netdev features etc).  Extend this support using BTF to cover
> arbitrary types.  "%pT" specifies the typed format, and the pointer
> argument is a "struct btf_ptr *" where struct btf_ptr is as follows:
> 
> struct btf_ptr {
> 	void *ptr;
> 	const char *type;
> 	u32 id;
> };
> 
> Either the "type" string ("struct sk_buff") or the BTF "id" can be
> used to identify the type to use in displaying the associated "ptr"
> value.  A convenience function to create and point at the struct
> is provided:
> 
> 	printk(KERN_INFO "%pT", BTF_PTR_TYPE(skb, struct sk_buff));
> 
> When invoked, BTF information is used to traverse the sk_buff *
> and display it.  Support is present for structs, unions, enums,
> typedefs and core types (though in the latter case there's not
> much value in using this feature of course).
> 
> Default output is indented, but compact output can be specified
> via the 'c' option.  Type names/member values can be suppressed
> using the 'N' option.  Zero values are not displayed by default
> but can be using the '0' option.  Pointer values are obfuscated
> unless the 'x' option is specified.  As an example:
> 
>   struct sk_buff *skb = alloc_skb(64, GFP_KERNEL);
>   pr_info("%pT", BTF_PTR_TYPE(skb, struct sk_buff));
> 
> ...gives us:
> 
> (struct sk_buff){
>  .transport_header = (__u16)65535,
> 	 .mac_header = (__u16)65535,
>  .end = (sk_buff_data_t)192,
>  .head = (unsigned char *)000000006b71155a,
>  .data = (unsigned char *)000000006b71155a,
>  .truesize = (unsigned int)768,
>  .users = (refcount_t){
>   .refs = (atomic_t){
>    .counter = (int)1,

Given

  #define BTF_INT_ENCODING(VAL)   (((VAL) & 0x0f000000) >> 24)

Maybe

  #define BTF_INT_SIGNED  (1 << 0)
  #define BTF_INT_CHAR    (1 << 1)
  #define BTF_INT_BOOL    (1 << 2)

could be extended to include

  #define BTF_INT_HEX     (1 << 3)

So hex values can be appropriately pretty-printed.



  reply	other threads:[~2020-05-13 23:05 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-12  5:56 [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alan Maguire
2020-05-12  5:56 ` [PATCH v2 bpf-next 1/7] bpf: provide function to get vmlinux BTF information Alan Maguire
2020-05-12  5:56 ` [PATCH v2 bpf-next 2/7] bpf: move to generic BTF show support, apply it to seq files/strings Alan Maguire
2020-05-13 23:04   ` Yonghong Song
2020-05-18  9:46     ` Alan Maguire
2020-05-19  6:21       ` Yonghong Song
2020-05-12  5:56 ` [PATCH v2 bpf-next 3/7] checkpatch: add new BTF pointer format specifier Alan Maguire
2020-05-12  5:56 ` [PATCH v2 bpf-next 4/7] printk: add type-printing %pT format specifier which uses BTF Alan Maguire
2020-05-13 23:05   ` Joe Perches [this message]
2020-05-13 23:07     ` Alexei Starovoitov
2020-05-13 23:22       ` Joe Perches
2020-05-14 23:43         ` Joe Perches
2020-05-15  0:09           ` Alexei Starovoitov
2020-05-15  0:21             ` Joe Perches
2020-05-14  0:45   ` Yonghong Song
2020-05-14 22:37     ` Alan Maguire
2020-05-15  0:39       ` Yonghong Song
2020-05-12  5:56 ` [PATCH v2 bpf-next 5/7] printk: extend test_printf to test %pT BTF-based format specifier Alan Maguire
2020-05-12  5:56 ` [PATCH v2 bpf-next 6/7] bpf: add support for %pT format specifier for bpf_trace_printk() helper Alan Maguire
2020-05-14  0:53   ` Yonghong Song
2020-05-18  9:10     ` Alan Maguire
2020-05-18 14:47       ` Yonghong Song
2020-05-12  5:56 ` [PATCH v2 bpf-next 7/7] bpf: add tests for %pT format specifier Alan Maguire
2020-05-15  0:21   ` Andrii Nakryiko
2020-05-13 22:24 ` [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alexei Starovoitov
2020-05-13 22:48   ` Joe Perches
2020-05-13 22:50     ` Alexei Starovoitov
2020-05-13 23:23       ` Joe Perches
2020-05-14 17:46   ` Alan Maguire
2020-05-15 18:59   ` Yonghong Song

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