linux-kernel - Re: [PATCH 10/26] dynamic_debug: enlarge command/query write buffer

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Date:	Wed, 21 Sep 2011 15:29:26 -0700
From:	Joe Perches <joe@...ches.com>
To:	jim.cromie@...il.com
Cc:	jbaron@...hat.com, bart.vanassche@...il.com, greg@...ah.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/26] dynamic_debug: enlarge command/query write buffer

On Wed, 2011-09-21 at 15:54 -0600, jim.cromie@...il.com wrote:
> From: Jim Cromie <jim.cromie@...il.com>
> 
> Current write buffer is 256 bytes, on stack.  Allocate it off heap,
> and enlarge it to 4096 bytes, big enough for ~100 queries (at 40 bytes
> each), and error out if not.  This should be enough for most uses, and
> others can be split into 2 writes.
> 
> This makes it play nicely with:
>  $> cat debug-queries-file > /dbg/dynamic_debug/control
[]
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
[]
> @@ -590,24 +590,32 @@ __setup("ddebug_query=", ddebug_setup_query);
>   * File_ops->write method for <debugfs>/dynamic_debug/conrol.  Gathers the
>   * command text from userspace, parses and executes it.
>   */
> +#define USER_BUF_PAGE 4095

Why not just read into a fifo and parse
it until empty?

>  static ssize_t ddebug_proc_write(struct file *file, const char __user *ubuf,
>  				  size_t len, loff_t *offp)
>  {
> -	char tmpbuf[256];
> +	char *tmpbuf;
>  	int ret;
>  
>  	if (len == 0)
>  		return 0;
> -	/* we don't check *offp -- multiple writes() are allowed */
> -	if (len > sizeof(tmpbuf)-1)
> +	if (len > USER_BUF_PAGE - 1) {
> +		pr_warn("expected <%d bytes into control \n", USER_BUF_PAGE);
>  		return -E2BIG;
> -	if (copy_from_user(tmpbuf, ubuf, len))
> +	}

kfifo_from_user?


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