MAC address data type

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A variable of type mac_addr_t is used to hold the value of MAC address. The MAC address data type is an abstract data type and you cannot use it directly with standard C unary or binary operators.

Only local or global variables of type mac_addr_t are supported.

A variable of this type can also be stored in an associate array either as a key or as a value.

Vue supports the following characteristics and operations for the MAC address type variables:

Declaration of MAC address variable 

mac_addr_t m1;           																				// global variable of type 
__auto mac_addr_t m2;                             // auto variable of type 
m2 = __etherhdr->src_addr;                        // store source MAC address in a local variable
mac_aso[“src_mac_addr”] = __etherhdr->src_addr ;  // store in an associative array.

The signed, unsigned, register, static, thread, and kernel qualifiers are not supported for the mac_addr_t type variables.

Assignment operation

The assignment (=) operator allows a mac_addr_t type variable to be assigned to another mac_addr_t type variable. The original values of the variable is overwritten. No typecasting is allowed from or to the mac_addr_t variable types.

In the following example, the content of the mac_addr_t m1 is assigned to m2. 

mac_addr_t m1, m2;              // Declares two MAC address variables. 
m1 = __etherhdr->src_addr;      // Get the source MAC address of the packet in m1. 
m2 = m1 ;                       // Get the content of m1 into m2.

Comparison operation

Only equality (==) and inequality (!=) operators are allowed for the mac_addr_t variables. The result of the equality operator is True (1) if both contains the same MAC address values or False (0) otherwise.

The inequality operator is the exact compliment of this behavior. No other comparison operators (>=, >, <, or =<) are allowed for the mac_addr_t type variables. 
if ( m1 == m2) // comparing two mac_addr_t type variables. 
printf(“Mac addresses are equal”); else printf(“Mac addresses are not equal”);

Printing MAC address type variables

A mac_addr_t type variable can be printed with “%M” format specifier in the printf() function of Vue. An associative array that has mac_addr_t type variables as key or value (or both) can be printed by using the print() function. 
printf(“ Source MAC address=[%M]\n”, __etherhdr->src_addr); 
mac_aso[“src_mac_address”] = __etherhdr->src_addr ; // Store source MAC address as value in an associative array mac_aso. 
print(mac_aso);
Limitations for MAC address type variable
  • The array of the mac_addr_t variable cannot be declared.
  • The mac_addr_t variables cannot be used as a member of a struct or a union.
  • Pointer to mac_addr_t variable is not allowed.
  • Typecasting of mac_addr_t variable to any other type or typecasting any other type to mac_addr_t type is not allowed.
  • No arithmetic operator (+, -, *, /, ++, -- etc) can be used with mac_addr_t type variable.