Re: [RFC v1] seq_buf: Add seq_buf_create() to implement DECLARE_SEQ_BUF()

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 29 Oct 2026 00:19:24 +0100
Alejandro Colomar <alx@kernel.org> wrote:

> This implements DECLARE_SEQ_BUF() in a way that is independent of the
> members of the structure.
> 
> This will allow transitioning to a different implementation of seq_buf
> which uses pointers instead of sizes, on which I plan to work soon.
> 
> The compiler should be able to optimize this out and produce the same
> code as before.
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Alejandro Colomar <alx@kernel.org>
> ---
> 
> Hi Steve, Kees,
> 
> This is a patch that I could split from the rewrite using pointers, so
> we can apply it earlier to reduce the later diff.
> 
> I've built a kernel with 'allmodconfig' to check that it's okay.
> 
> The reason I need this patch is that we can't calculate the end pointer
> of the compound literal without passing it to a function.  If you want
> me to hold this patch and send it together with the rest of the rewrite,
> I can also do that, but I thought this might be useful by itself.
> 
> 
> Have a lovely night!
> Alex
> 
> 
>  include/linux/seq_buf.h | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
> index 9f2839e73f8a..facc5643c049 100644
> --- a/include/linux/seq_buf.h
> +++ b/include/linux/seq_buf.h
> @@ -25,10 +25,7 @@ struct seq_buf {
>  };
>  
>  #define DECLARE_SEQ_BUF(NAME, SIZE)			\
> -	struct seq_buf NAME = {				\
> -		.buffer = (char[SIZE]) { 0 },		\
> -		.size = SIZE,				\
> -	}
> +	struct seq_buf NAME = seq_buf_create((char[SIZE]){0}, SIZE)

It can't use the DECLARE_* name as that is by default something that
can be used outside of a function:

  DECLARE_SEQ_BUF(foo, 1024);

Needs to work. Just because nothing does that now, doesn't mean it will
not happen in the future. From my understanding, all DECLARE_* macros
for other types work this way.

-- Steve


>  
>  static inline void seq_buf_clear(struct seq_buf *s)
>  {
> @@ -45,6 +42,15 @@ seq_buf_init(struct seq_buf *s, char *buf, unsigned int size)
>  	seq_buf_clear(s);
>  }
>  
> +static inline struct seq_buf
> +seq_buf_create(char *buf, unsigned int size)
> +{
> +	struct seq_buf  s;
> +
> +	seq_buf_init(&s, buf, size);
> +	return s;
> +}
> +
>  /*
>   * seq_buf have a buffer that might overflow. When this happens
>   * len is set to be greater than size.
> 
> Range-diff against v0:
> -:  ------------ > 1:  9bda534b33f0 seq_buf: Add seq_buf_create() to implement DECLARE_SEQ_BUF()