linux-kernel - Re: [RFC PATCH 4/6] seq_file: add function to write binary data

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Message-Id: <20080505213644.b153ee68.akpm@linux-foundation.org>
Date:	Mon, 5 May 2008 21:36:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Oberparleiter <peter.oberparleiter@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, ltp-list@...ts.sourceforge.net,
	ltp-coverage@...ts.sourceforge.net,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH 4/6] seq_file: add function to write binary data

On Mon, 05 May 2008 17:24:37 +0200 Peter Oberparleiter <peter.oberparleiter@...ibm.com> wrote:

> From: Peter Oberparleiter <peter.oberparleiter@...ibm.com>
> 
> seq_write() can be used to construct seq_files containing arbitrary
> data. Required by the gcov-profiling interface to synthesize binary
> profiling data files.
> 
> Signed-off-by: Peter Oberparleiter <peter.oberparleiter@...ibm.com>
> ---
>  fs/seq_file.c            |   12 ++++++++++++
>  include/linux/seq_file.h |    1 +
>  2 files changed, 13 insertions(+)
> 
> Index: linux-2.6.26-rc1/fs/seq_file.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/fs/seq_file.c
> +++ linux-2.6.26-rc1/fs/seq_file.c
> @@ -554,6 +554,18 @@ int seq_puts(struct seq_file *m, const c
>  }
>  EXPORT_SYMBOL(seq_puts);
>  
> +int seq_write(struct seq_file *m, const void *s, size_t len)

Most of the other seq_file interface functions are nicely documented.

> +{
> +	if (m->count + len < m->size) {

Are you sure that shouldn't be >=?

> +		memcpy(m->buf + m->count, s, len);
> +		m->count += len;
> +		return 0;
> +	}
> +	m->count = m->size;
> +	return -1;
> +}
> +EXPORT_SYMBOL(seq_write);

Usually when a write-style function is passed too much data it will write
as much as it can and will then return a smaller-than-requested value.

That's inappropriate for your application of seq_write(), but perhaps is
appropriate for other future callers?

This function has an upper limit of PAGE_SIZE bytes, I think?  The covering
documentation should explain such things.

>  struct list_head *seq_list_start(struct list_head *head, loff_t pos)
>  {
>  	struct list_head *lh;
> Index: linux-2.6.26-rc1/include/linux/seq_file.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/linux/seq_file.h
> +++ linux-2.6.26-rc1/include/linux/seq_file.h
> @@ -39,6 +39,7 @@ int seq_release(struct inode *, struct f
>  int seq_escape(struct seq_file *, const char *, const char *);
>  int seq_putc(struct seq_file *m, char c);
>  int seq_puts(struct seq_file *m, const char *s);
> +int seq_write(struct seq_file *m, const void *s, size_t len);
>  
>  int seq_printf(struct seq_file *, const char *, ...)
>  	__attribute__ ((format (printf,2,3)));
> 
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