bonding: comparing a u8 with -1 is always false

slave->duplex is a u8 type so the in bond_info_show_slave() when we
check "if (slave->duplex == -1)", it's always false.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

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Dan Carpenter <dan.carpenter@oracle.com> wrote:
>slave->duplex is a u8 type so the in bond_info_show_slave() when we
>check "if (slave->duplex == -1)", it's always false.
>
>Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index b2b9109..b0c5772 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -560,8 +560,8 @@ static int bond_update_speed_duplex(struct slave *slave)
> 	u32 slave_speed;
> 	int res;
>
>-	slave->speed = -1;
>-	slave->duplex = -1;
>+	slave->speed = SPEED_UNKNOWN;
>+	slave->duplex = DUPLEX_UNKNOWN;
>
> 	res = __ethtool_get_settings(slave_dev, &ecmd);
> 	if (res < 0)
>diff --git a/drivers/net/bonding/bond_procfs.c b/drivers/net/bonding/bond_procfs.c
>index 2acf0b0..ad284ba 100644
>--- a/drivers/net/bonding/bond_procfs.c
>+++ b/drivers/net/bonding/bond_procfs.c
>@@ -158,12 +158,12 @@ static void bond_info_show_slave(struct seq_file *seq,
> 	seq_printf(seq, "\nSlave Interface: %s\n", slave->dev->name);
> 	seq_printf(seq, "MII Status: %s\n",
> 		   (slave->link == BOND_LINK_UP) ?  "up" : "down");
>-	if (slave->speed == -1)
>+	if (slave->speed == SPEED_UNKNOWN)
> 		seq_printf(seq, "Speed: %s\n", "Unknown");
> 	else
> 		seq_printf(seq, "Speed: %d Mbps\n", slave->speed);

	Since you #define SPEED_UNKNOWN to -1 (below), how does this
actually change anything?  Did you mean 0xffff (because struct
ethtool_cmd's speed is a u16)?

	Running on a moderately recent net-next (without the very recent
change to bond_update_speed_duplex), I see that bonding indeed doesn't
get the speed or duplex correct after a cable pull:

Slave Interface: eth2
MII Status: down
Speed: 100 Mbps
Duplex: full

	so perhaps a rational (unsigned-friendly) SPEED_UNKNOWN and
DUPLEX_UNKNOWN are needed, but I'm not sure how this #define actually
would change any behavior in the bonding case.

>-	if (slave->duplex == -1)
>+	if (slave->duplex == DUPLEX_UNKNOWN)
> 		seq_printf(seq, "Duplex: %s\n", "Unknown");
> 	else
> 		seq_printf(seq, "Duplex: %s\n", slave->duplex ? "full" : "half");

	This one might "work," but it seems to depend on the fact that
the integral conversion of -1 to an 8 bit unsigned type will be 255
(0xff).  I believe that's true (according to the ISO C copy I have
handy), but I'm not sure that kind of implicit assumption should be
built into the code.  At least not without some explanation.

	-J

>diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
>index 45f00b6..de33de1 100644
>--- a/include/linux/ethtool.h
>+++ b/include/linux/ethtool.h
>@@ -1097,10 +1097,12 @@ struct ethtool_ops {
> #define SPEED_1000		1000
> #define SPEED_2500		2500
> #define SPEED_10000		10000
>+#define SPEED_UNKNOWN		-1
>
> /* Duplex, half or full. */
> #define DUPLEX_HALF		0x00
> #define DUPLEX_FULL		0x01
>+#define DUPLEX_UNKNOWN		0xff
>
> /* Which connector port. */
> #define PORT_TP			0x00

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@us.ibm.com

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On Fri, 2011-11-04 at 13:02 -0700, Jay Vosburgh wrote:
> Dan Carpenter <dan.carpenter@oracle.com> wrote:
> >slave->duplex is a u8 type so the in bond_info_show_slave() when we
> >check "if (slave->duplex == -1)", it's always false.
> >
> >Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> >
> >diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> >index b2b9109..b0c5772 100644
> >--- a/drivers/net/bonding/bond_main.c
> >+++ b/drivers/net/bonding/bond_main.c
> >@@ -560,8 +560,8 @@ static int bond_update_speed_duplex(struct slave *slave)
> > 	u32 slave_speed;
> > 	int res;
> >
> >-	slave->speed = -1;
> >-	slave->duplex = -1;
> >+	slave->speed = SPEED_UNKNOWN;
> >+	slave->duplex = DUPLEX_UNKNOWN;
> >
> > 	res = __ethtool_get_settings(slave_dev, &ecmd);
> > 	if (res < 0)
> >diff --git a/drivers/net/bonding/bond_procfs.c b/drivers/net/bonding/bond_procfs.c
> >index 2acf0b0..ad284ba 100644
> >--- a/drivers/net/bonding/bond_procfs.c
> >+++ b/drivers/net/bonding/bond_procfs.c
> >@@ -158,12 +158,12 @@ static void bond_info_show_slave(struct seq_file *seq,
> > 	seq_printf(seq, "\nSlave Interface: %s\n", slave->dev->name);
> > 	seq_printf(seq, "MII Status: %s\n",
> > 		   (slave->link == BOND_LINK_UP) ?  "up" : "down");
> >-	if (slave->speed == -1)
> >+	if (slave->speed == SPEED_UNKNOWN)
> > 		seq_printf(seq, "Speed: %s\n", "Unknown");
> > 	else
> > 		seq_printf(seq, "Speed: %d Mbps\n", slave->speed);
> 
> 	Since you #define SPEED_UNKNOWN to -1 (below), how does this
> actually change anything?  Did you mean 0xffff (because struct
> ethtool_cmd's speed is a u16)?

The speed in ethtool_cmd is 32 bits divided between two fields.

> 	Running on a moderately recent net-next (without the very recent
> change to bond_update_speed_duplex), I see that bonding indeed doesn't
> get the speed or duplex correct after a cable pull:
> 
> Slave Interface: eth2
> MII Status: down
> Speed: 100 Mbps
> Duplex: full
> 
> 	so perhaps a rational (unsigned-friendly) SPEED_UNKNOWN and
> DUPLEX_UNKNOWN are needed, but I'm not sure how this #define actually
> would change any behavior in the bonding case.

Agree that they should be defined somewhere.  The ethtool utility
recognises speed values of 0, (u16)(-1) and (u32)(-1) as 'unknown'.
Personally I think 0 makes more sense than (u32)(-1) but it doesn't
matter much.

> >-	if (slave->duplex == -1)
> >+	if (slave->duplex == DUPLEX_UNKNOWN)
> > 		seq_printf(seq, "Duplex: %s\n", "Unknown");
> > 	else
> > 		seq_printf(seq, "Duplex: %s\n", slave->duplex ? "full" : "half");
> 
> 	This one might "work," but it seems to depend on the fact that
> the integral conversion of -1 to an 8 bit unsigned type will be 255
> (0xff).  I believe that's true (according to the ISO C copy I have
> handy), but I'm not sure that kind of implicit assumption should be
> built into the code.  At least not without some explanation.
[...]

It's true and does not need explanation.  Quite why anyone expected a
negative value to survive conversion to u8 and back to int, now that
deserves explanation...

Ben.

On Fri, Nov 04, 2011 at 01:02:01PM -0700, Jay Vosburgh wrote:
> 
> 	Since you #define SPEED_UNKNOWN to -1 (below), how does this
> actually change anything?  Did you mean 0xffff (because struct
> ethtool_cmd's speed is a u16)?
> 

Sorry I could have explained this better in the changelog.  The
slave->speed is stored in a u32 and the -1 works fine as is.
Obviously, as you point out the define doesn't change anything.  I
just changed it so it would look symetric with DUPLEX_UNKNOWN.

But I think you missed that I defined #define DUPLEX_UNKNOWN 0xff.
Before it we used a -1 for both and that didn't work.

I can resend this with a note about the SPEED_UNKNOWN cleanup if
you'd like.  I'll do that tomorrow or Sunday.

regards,
dan carpenter

From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Fri, 4 Nov 2011 23:53:51 +0300

> On Fri, Nov 04, 2011 at 01:02:01PM -0700, Jay Vosburgh wrote:
>> 
>> 	Since you #define SPEED_UNKNOWN to -1 (below), how does this
>> actually change anything?  Did you mean 0xffff (because struct
>> ethtool_cmd's speed is a u16)?
>> 
> 
> Sorry I could have explained this better in the changelog.  The
> slave->speed is stored in a u32 and the -1 works fine as is.
> Obviously, as you point out the define doesn't change anything.  I
> just changed it so it would look symetric with DUPLEX_UNKNOWN.
> 
> But I think you missed that I defined #define DUPLEX_UNKNOWN 0xff.
> Before it we used a -1 for both and that didn't work.
> 
> I can resend this with a note about the SPEED_UNKNOWN cleanup if
> you'd like.  I'll do that tomorrow or Sunday.

That won't be necessary, I'll apply your patch as-is.

Thanks Dan.
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