linux-kernel - Re: [PATCHv3] seq_buf: add seq_buf_do

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Date:   Sat, 15 Apr 2023 23:17:29 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] seq_buf: add seq_buf_do_printk() helper

On Sat, Apr 15, 2023 at 3:01 AM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> Sometimes we use seq_buf to format a string buffer, which
> we then pass to printk(). However, in certain situations
> the seq_buf string buffer can get too big, exceeding the
> PRINTKRB_RECORD_MAX bytes limit, and causing printk() to
> truncate the string.
>
> Add a new seq_buf helper. This helper prints the seq_buf
> string buffer line by line, using \n as a delimiter,
> rather than passing the whole string buffer to printk()
> at once.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Reviewed-by: Petr Mladek <pmladek@...e.com>

Tested-by: Yosry Ahmed <yosryahmed@...gle.com>

Thanks!
> ---
>  include/linux/seq_buf.h |  2 ++
>  lib/seq_buf.c           | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+)
>
> diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
> index 5b31c5147969..515d7fcb9634 100644
> --- a/include/linux/seq_buf.h
> +++ b/include/linux/seq_buf.h
> @@ -159,4 +159,6 @@ extern int
>  seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
>  #endif
>
> +void seq_buf_do_printk(struct seq_buf *s, const char *lvl);
> +
>  #endif /* _LINUX_SEQ_BUF_H */
> diff --git a/lib/seq_buf.c b/lib/seq_buf.c
> index 0a68f7aa85d6..45c450f423fa 100644
> --- a/lib/seq_buf.c
> +++ b/lib/seq_buf.c
> @@ -93,6 +93,38 @@ int seq_buf_printf(struct seq_buf *s, const char *fmt, ...)
>  }
>  EXPORT_SYMBOL_GPL(seq_buf_printf);
>
> +/**
> + * seq_buf_do_printk - printk seq_buf line by line
> + * @s: seq_buf descriptor
> + * @lvl: printk level
> + *
> + * printk()-s a multi-line sequential buffer line by line. The function
> + * makes sure that the buffer in @s is nul terminated and safe to read
> + * as a string.
> + */
> +void seq_buf_do_printk(struct seq_buf *s, const char *lvl)
> +{
> +       const char *start, *lf;
> +
> +       if (s->size == 0 || s->len == 0)
> +               return;
> +
> +       seq_buf_terminate(s);
> +
> +       start = s->buffer;
> +       while ((lf = strchr(start, '\n'))) {
> +               int len = lf - start + 1;
> +
> +               printk("%s%.*s", lvl, len, start);
> +               start = ++lf;
> +       }
> +
> +       /* No trailing LF */
> +       if (start < s->buffer + s->len)
> +               printk("%s%s\n", lvl, start);
> +}
> +EXPORT_SYMBOL_GPL(seq_buf_do_printk);
> +
>  #ifdef CONFIG_BINARY_PRINTF
>  /**
>   * seq_buf_bprintf - Write the printf string from binary arguments
> --
> 2.40.0.634.g4ca3ef3211-goog
>