* @param type the type that has the field "xreq" (ex: "struct mystruct")
* @param x the pointer to the field "xreq"
* @return the pointer to the structure that contains the field "xreq" of address 'x'
* @param type the type that has the field "xreq" (ex: "struct mystruct")
* @param x the pointer to the field "xreq"
* @return the pointer to the structure that contains the field "xreq" of address 'x'