netdev - Re: [PATCH 1/2] net: dsa: mv88e6xxx: add write access to debugfs regs file

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Date:	Wed, 8 Jul 2015 22:53:48 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Guenter Roeck <linux@...ck-us.net>,
	linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com
Subject: Re: [PATCH 1/2] net: dsa: mv88e6xxx: add write access to debugfs
 regs file

On Wed, Jul 08, 2015 at 04:36:18PM -0400, Vivien Didelot wrote:
> Allow write access to the regs file in the debugfs interface, with the
> following parameters:
> 
>     echo <name> <reg> <value> > regs
> 
> Where "name" is the register name (as shown in the header row), "reg" is
> the register address (as shown in the first column) and "value" is the
> 16-bit value. e.g.:
> 
>     echo GLOBAL 1a 5550 > regs
> 
> Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
> ---
>  drivers/net/dsa/mv88e6xxx.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/dsa/mv88e6xxx.c b/drivers/net/dsa/mv88e6xxx.c
> index 8c130c0..04e6eb6 100644
> --- a/drivers/net/dsa/mv88e6xxx.c
> +++ b/drivers/net/dsa/mv88e6xxx.c
> @@ -1648,6 +1648,35 @@ static int mv88e6xxx_regs_show(struct seq_file *s, void *p)
>  	return 0;
>  }
>  
> +static ssize_t mv88e6xxx_regs_write(struct file *file, const char __user *buf,
> +				    size_t count, loff_t *ppos)
> +{
> +	struct seq_file *s = file->private_data;
> +	struct dsa_switch *ds = s->private;
> +	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
> +	char name[count];

Is this safe? Is count somehow limited? If i was to echo 8K to the
file would i not exceed the kernel stack space?

     Andrew
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