linux-kernel - Re: [PATCH] seq_buf: make DECLARE_SEQ

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Date: Tue, 16 Jan 2024 20:40:29 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: nathanl@...ux.ibm.com, "Steven Rostedt (Google)" <rostedt@...dmis.org>,
 Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] seq_buf: make DECLARE_SEQ_BUF() usable

Le 16/01/2024 à 15:09, Nathan Lynch via B4 Relay a écrit :
> From: Nathan Lynch <nathanl@...ux.ibm.com>
> 
> Using the address operator on the array doesn't work:
> 
> /include/linux/seq_buf.h:27:27: error: initialization of ‘char *’
>    from incompatible pointer type ‘char (*)[128]’
>    [-Werror=incompatible-pointer-types]
>     27 |                 .buffer = &__ ## NAME ## _buffer,       \
>        |                           ^
> 
> Apart from fixing that, we can improve DECLARE_SEQ_BUF() by using a
> compound literal to define the buffer array without attaching a name
> to it. This makes the macro a single statement, allowing constructs
> such as:
> 
>    static DECLARE_SEQ_BUF(my_seq_buf, MYSB_SIZE);
> 
> to work as intended.
> 
> Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
> Fixes: dcc4e5728eea ("seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_str()")
> ---
>   include/linux/seq_buf.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
> index 5fb1f12c33f9..c44f4b47b945 100644
> --- a/include/linux/seq_buf.h
> +++ b/include/linux/seq_buf.h
> @@ -22,9 +22,8 @@ struct seq_buf {
>   };
>   
>   #define DECLARE_SEQ_BUF(NAME, SIZE)			\
> -	char __ ## NAME ## _buffer[SIZE] = "";		\
>   	struct seq_buf NAME = {				\
> -		.buffer = &__ ## NAME ## _buffer,	\
> +		.buffer = (char[SIZE]) { 0 },		\
>   		.size = SIZE,				\
>   	}

Hi,

just removing the & in ".buffer = __ ## NAME ## _buffer, \" also works IIRC.

See [1], which unfortunately has been unnoticed.

CJ


[1]: 
https://lore.kernel.org/all/2a534333-b5f6-4b1d-b4b8-a1a71f91c3ff@wanadoo.fr/


>   
> 
> ---
> base-commit: 70d201a40823acba23899342d62bc2644051ad2e
> change-id: 20240112-declare-seq-buf-fix-9803b7e679bc
> 
> Best regards,