netdev - Re: [PATCH] net: tulip: Remove private "strncmp"

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Date:	Thu, 4 Dec 2014 11:35:55 -0800
From:	Grant Grundler <grantgrundler@...il.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	"open list:TULIP NETWORK DRI..." <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: tulip: Remove private "strncmp"

On Thu, Dec 4, 2014 at 2:30 AM, Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> The comment says that the built-in strncmp didn't work. That is not
> surprising, as apparently "str" semantics are not really what is
> wanted (hint: de4x5_strncmp only stops when two different bytes are
> encountered or the end is reached; not if either byte happens to be
> 0). de4x5_strncmp is actually a memcmp (except for the signature and
> that bytes are not necessarily treated as unsigned char); since only
> the boolean value of the result is used we can just replace
> de4x5_strncmp with memcmp.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>
> Notes:
>     I don't know if the comment meant to say 3 bytes, or if the code
>     compares meaningful chunks of memory (the first three bytes of
>     &lp->srom span 1.5 fields, and the three bytes from (char*)&lp->srom +
>     0x10 are &lp->srom.{id_block_crc,reserved2,version} - it seems odd
>     that these chunks should ever be equal to each other and to the
>     enet_det[i]). Whether or not the current code works, this patch
>     shouldn't change the semantics, and I'd like to get rid of
>     de4x5_strncmp since it is not, in fact, a strncmp.

+1 I think your analysis is correct. The function appears to be
checking against a black list of MAC addresses that has two "broken"
devices MAC addresses.

Acked-by: Grant Grundler <grundler@...isc-linux.org>

thanks,
grant

ps. I don't like how de4x5_bad_srom() is structured but I can't test
these devices either.  Specifically, the offset of the MAC address
should be known and we should only be testing that offset to see if
it's "that vendor".

>  drivers/net/ethernet/dec/tulip/de4x5.c | 20 +++-----------------
>  1 file changed, 3 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/ethernet/dec/tulip/de4x5.c b/drivers/net/ethernet/dec/tulip/de4x5.c
> index cf8b6ff..badff18 100644
> --- a/drivers/net/ethernet/dec/tulip/de4x5.c
> +++ b/drivers/net/ethernet/dec/tulip/de4x5.c
> @@ -995,7 +995,6 @@ static void    de4x5_dbg_mii(struct net_device *dev, int k);
>  static void    de4x5_dbg_media(struct net_device *dev);
>  static void    de4x5_dbg_srom(struct de4x5_srom *p);
>  static void    de4x5_dbg_rx(struct sk_buff *skb, int len);
> -static int     de4x5_strncmp(char *a, char *b, int n);
>  static int     dc21041_infoleaf(struct net_device *dev);
>  static int     dc21140_infoleaf(struct net_device *dev);
>  static int     dc21142_infoleaf(struct net_device *dev);
> @@ -4102,8 +4101,7 @@ get_hw_addr(struct net_device *dev)
>  }
>
>  /*
> -** Test for enet addresses in the first 32 bytes. The built-in strncmp
> -** didn't seem to work here...?
> +** Test for enet addresses in the first 32 bytes.
>  */
>  static int
>  de4x5_bad_srom(struct de4x5_private *lp)
> @@ -4111,8 +4109,8 @@ de4x5_bad_srom(struct de4x5_private *lp)
>      int i, status = 0;
>
>      for (i = 0; i < ARRAY_SIZE(enet_det); i++) {
> -       if (!de4x5_strncmp((char *)&lp->srom, (char *)&enet_det[i], 3) &&
> -           !de4x5_strncmp((char *)&lp->srom+0x10, (char *)&enet_det[i], 3)) {
> +       if (!memcmp(&lp->srom, &enet_det[i], 3) &&
> +           !memcmp((char *)&lp->srom+0x10, &enet_det[i], 3)) {
>             if (i == 0) {
>                 status = SMC;
>             } else if (i == 1) {
> @@ -4125,18 +4123,6 @@ de4x5_bad_srom(struct de4x5_private *lp)
>      return status;
>  }
>
> -static int
> -de4x5_strncmp(char *a, char *b, int n)
> -{
> -    int ret=0;
> -
> -    for (;n && !ret; n--) {
> -       ret = *a++ - *b++;
> -    }
> -
> -    return ret;
> -}
> -
>  static void
>  srom_repair(struct net_device *dev, int card)
>  {
> --
> 2.0.4
>
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