Location of the SA
Each SM incorporates an SA. Whether or not an SM's SA actually resides at the same physical location (i.e., the same port/QP combination) as the SM is SM implementation-specific. The location (i.e., port LID address) of the Master SM is stored each port's PortInfo.MasterSMLID attribute element. The location of the Master SM's SA may be ascertained in one of two ways:
Performing a read of the SA's ClassPortInfo attribute by issuing a SubnAdm Get(ClassPortInfo) GMP to the port specified by the issuing port's PortInfo.MasterSMLID attribute element. The GMP must have the following characteristics:
- The SL used must be the one specified in the PortInfo.MasterSMSL attribute element.
- The packet's SLID must be set to the base LID address of the issuing port.
- The destination QP (BTH:DestQP) must be QP1 (the GSI).
- The DETH:Q_Key in the GMP must be the controlled Q_Key 80010000h.
- The packet's BTH:P_Key must be set to the default P_Key (FFFFh or 7FFFh) placed in the issuing port's P_KeyTable by the Master SM.
The specification states that the ClassPortInfo data structure returned (see Table 28-7 on page 794) “shall return all information needed to communicate to Subnet Administration.” However, it doesn't say what field(s) of the data structure contain this information. It is the author's opinion that it works as follows:
- If the ClassPortInfo.RedirectLID field is zero, redirection is not in effect. All SA accesses are therefore sent to the same port that the SM resides on (i.e., the one identified by the issuing port's PortInfo.MasterSMLID attribute element).
- If, on the other hand, the RedirectLID attribute element is non-zero, redirection is in force and all SA request MADs should be sent to the indicated redirect address. For more information on redirection, refer to “GMP Redirection” on page 175 and “Additional Information Regarding Redirection” on page 914.
The location of the SA may also be ascertained by initially assuming that it resides at the same port as the Master SM (i.e., the port located at the LID address contained in the initiating port's PortInfo.MasterSMLID attribute element). The entity desiring to access the SA issues a SubnAdm GMP to QP1 at that port LID address:
- If the SA resides at the same port address as the SM, the attribute access attempt will succeed.
- If the SA resides at a different location, the SA attribute access attempt will result in a response GMP with the Status field indicating that all SA access requests must be redirected to the redirect address specified in the copy of the ClassPortInfo attribute that is returned in the response MAD's data field.