net: add ETHER_IS_ZERO macro similar to ETHER_IS_BROADCAST

[jacob.e.keller_intel.com]

Summary

Some places in network code may need to verify that an ethernet address
is not the 'zero' address. Provide a standard macro ETHER_IS_ZERO for
this purpose, similar to the ETHER_IS_BROADCAST macro already available.

Signed-off-by: Jacob Keller <[e-mail]>

[afedorov]

sys/net/ethernet.h

79

Is this correct? If one byte of mac address is equal zero than the whole expression equal 0x00.

[jacob.e.keller_intel.com]

sys/net/ethernet.h

79

Yea, this is incorrect, woops. Should be bitwise or.

[jacob.e.keller_intel.com]

Use bitwise OR instead of bitwise AND to correct implementation

[afedorov]

It’s seems I found another incorrect solution:

#include <stdio.h>

int main()
{

unsigned char a = (1 << 0) ||(1<<1)||(1 <<2)||(1<<3)||(1<<4)||(1<<5);
printf("momentum more : %d\n", a);

return 0;

}

[jacob.e.keller_intel.com]

In D21240#462131, @aleksandr.fedorov_itglobal.com wrote:

It’s seems I found another incorrect solution:

#include <stdio.h>

int main()
{

unsigned char a = (1 << 0) ||(1<<1)||(1 <<2)||(1<<3)||(1<<4)||(1<<5);
printf("momentum more : %d\n", a);

return 0;

}

In D21240#462131, @aleksandr.fedorov_itglobal.com wrote:

It’s seems I found another incorrect solution:

#include <stdio.h>

int main()
{

unsigned char a = (1 << 0) ||(1<<1)||(1 <<2)||(1<<3)||(1<<4)||(1<<5);
printf("momentum more : %d\n", a);

return 0;

}

This uses boolean ||, not bitwise |

bitwise OR should correctly combine all of the chunks of the MAC address, and if any are non-zero, the whole thing will be non-zero.

[afedorov]

Ops, you’re right. Sorry for the noise.

[erj]

I get a build error with this revision:

--- if_ure.o ---
/root/srcs/head/src/sys/dev/usb/net/if_ure.c:71:9: error: 'ETHER_IS_ZERO' macro redefined [-Werror,-Wmacro-redefined]
#define ETHER_IS_ZERO(addr) \
        ^
/root/srcs/head/src/sys/net/ethernet.h:77:9: note: previous definition is here
#define ETHER_IS_ZERO(addr) \
        ^
1 error generated.

[jacob.e.keller_intel.com]

Remove ETHER_IS_ZERO definitions from USB networking drivers.

[erj]

Builds okay now.