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

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Date: Wed, 17 Jan 2024 12:29:49 -0800
From: Kees Cook <keescook@...omium.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm.com@...nel.org>,
	nathanl@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] seq_buf: make DECLARE_SEQ_BUF() usable

On Wed, Jan 17, 2024 at 09:32:34AM -0500, Steven Rostedt wrote:
> 
> Kees,
> 
> Are you OK with this change? I ran it through my tests and have another
> pull request ready to go that includes this. But I don't want to send it
> without an Acked-by from you.

Yeah! This cleanly solves the lack of being able to add the "static",
etc.

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> 
> Luckily, Linus is on non-voluntary vacation so we may still have time ;-)
> 
> -- Steve
> 
> 
> On Tue, 16 Jan 2024 08:09:25 -0600
> Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm.com@...nel.org> wrote:
> 
> > 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,				\
> >  	}
> >  
> > 
> > ---
> > base-commit: 70d201a40823acba23899342d62bc2644051ad2e
> > change-id: 20240112-declare-seq-buf-fix-9803b7e679bc
> > 
> > Best regards,
> 

-- 
Kees Cook