The alias lfi lets you disassemble all of the instructions in a single function. Instructions from other functions may be intermixed in the disassembly due to compiler optimizations. The following example shows how to disassemble a member function:
(idb)alias lfi
lfi(x) set $lfitmp = x ; $lfitmp, $highpc($lfitmp) / i ; unset $lfitmp
(idb) lfi( Node::getNextNode )
class Node* Node::getNextNode(void): src/x_list.cxx
[line 81, 0x0804b5aa] getNextNode: pushl %ebp
[line 81, 0x0804b5ab] getNextNode+0x1: movl %esp, %ebp
[line 81, 0x0804b5ad] getNextNode+0x3: movl 0x8(%ebp), %eax
[line 81, 0x0804b5b0] getNextNode+0x6: movl 0x4(%eax), %eax
[line 81, 0x0804b5b3] getNextNode+0x9: leave
[line 81, 0x0804b5b4] getNextNode+0xa: ret
[line 81, 0x0804b5b5] getNextNode+0xb: nop
(idb)