boot: add a new type to halt booting

Current seabios will try to boot from selected devices first,
if they are all failed, seabios will also try to boot from
un-selected devices.

For example:
@ qemu-kvm -boot order=n,menu=on ...

Guest will boot from network first, if it's failed, guest will try to
boot from other un-selected devices (floppy, cdrom, disk) one by one.

We need to make it configurable. This patch added a new type, qemu can
add "HALT" at the end of bootindex string, then seabios will halt
booting after trying to boot from selected devices.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Signed-off-by: Amos Kong <akong@redhat.com>

src/boot.c

@@ -291,6 +291,7 @@ static struct bootentry_s *BootList;
 #define IPL_TYPE_CBFS        0x20
 #define IPL_TYPE_BEV         0x80
 #define IPL_TYPE_BCV         0x81
+#define IPL_TYPE_HALT        0xf0
 
 static void
 bootentry_add(int type, int prio, u32 data, const char *desc)
@@ -488,6 +489,11 @@ boot_prep(void)
     interactive_bootmenu();
     wait_threads();
 
+    int haltprio = find_prio("HALT");
+
+    if (haltprio >= 0)
+        bootentry_add(IPL_TYPE_HALT, haltprio, 0, "HALT");
+
     // Map drives and populate BEV list
     struct bootentry_s *pos = BootList;
     while (pos) {
@@ -672,6 +678,9 @@ do_boot(int seq_nr)
     case IPL_TYPE_BEV:
         boot_rom(ie->vector);
         break;
+    case IPL_TYPE_HALT:
+        boot_fail();
+        break;
     }
 
     // Boot failed: invoke the boot recovery function