[Qemu-devel] [SeaBIOS PATCH v2] boot: support strict boot and make it configurable

[Amos Kong <akong@redhat.com>]

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, seabios user can config it by a rom
file('etc/boot-strict'). 'strict boot' means only boot from user
selected devices.

I added some comments in this patch to explain why we can judge if
device is selected or not by DEFAULT_PRIO(9999). I also added 'selected'
flag in struct bootentry_s and struct bev_s to make it clearer.

If this patch is accepted, I will add a boot option (-boot strict=on)
for qemu.

Signed-off-by: Amos Kong <akong@redhat.com>
---
 src/boot.c |   31 ++++++++++++++++++++++++-------
 1 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/boot.c b/src/boot.c
index c67cc7f..99ac791 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -92,6 +92,7 @@ find_prio(const char *glob)
     int i;
     for (i = 0; i < BootorderCount; i++)
         if (glob_prefix(glob, Bootorder[i]))
+            // device exists in the Bootorder list loaded from rom file
             return i+1;
     return -1;
 }
@@ -249,12 +250,14 @@ boot_setup(void)
             CheckFloppySig = 0;
         u32 bootorder = (inb_cmos(CMOS_BIOS_BOOTFLAG2)
                          | ((inb_cmos(CMOS_BIOS_BOOTFLAG1) & 0xf0) << 4));
+        // reset device priority to default DEFAULT_PRIO(9999)
         DefaultFloppyPrio = DefaultCDPrio = DefaultHDPrio
             = DefaultBEVPrio = DEFAULT_PRIO;
         int i;
         for (i=101; i<104; i++) {
             u32 val = bootorder & 0x0f;
             bootorder >>= 4;
+            // priority of devices selected in bootorder will be changed
             switch (val) {
             case 1: DefaultFloppyPrio = i; break;
             case 2: DefaultHDPrio = i;     break;
@@ -280,6 +283,7 @@ struct bootentry_s {
         struct drive_s *drive;
     };
     int priority;
+    int selected;
     const char *description;
     struct bootentry_s *next;
 };
@@ -304,6 +308,9 @@ bootentry_add(int type, int prio, u32 data, const char *desc)
     }
     be->type = type;
     be->priority = prio;
+    // set 'selected' flag according to the priority
+    if (prio != DEFAULT_PRIO)
+        be->selected = 1;
     be->data = data;
     be->description = desc ?: "?";
     dprintf(3, "Registering bootable: %s (type:%d prio:%d data:%x)\n"
@@ -332,6 +339,8 @@ bootentry_add(int type, int prio, u32 data, const char *desc)
 }
 
 // Return the given priority if it's set - defaultprio otherwise.
+// This function is called by boot_add_*(), it will only pass
+// DEFAULT_PRIO(9999) for unselected devices as the boot-entry priority.
 static inline int defPrio(int priority, int defaultprio) {
     return (priority < 0) ? defaultprio : priority;
 }
@@ -454,13 +463,14 @@ interactive_bootmenu(void)
 struct bev_s {
     int type;
     u32 vector;
+    int selected;
 };
 static struct bev_s BEV[20];
 static int BEVCount;
 static int HaveHDBoot, HaveFDBoot;
 
 static void
-add_bev(int type, u32 vector)
+add_bev(int type, u32 vector, int selected)
 {
     if (type == IPL_TYPE_HARDDISK && HaveHDBoot++)
         return;
@@ -471,6 +481,7 @@ add_bev(int type, u32 vector)
     struct bev_s *bev = &BEV[BEVCount++];
     bev->type = type;
     bev->vector = vector;
+    bev->selected = selected;
 }
 
 // Prepare for boot - show menu and run bcvs.
@@ -494,29 +505,29 @@ boot_prep(void)
         switch (pos->type) {
         case IPL_TYPE_BCV:
             call_bcv(pos->vector.seg, pos->vector.offset);
-            add_bev(IPL_TYPE_HARDDISK, 0);
+            add_bev(IPL_TYPE_HARDDISK, 0, pos->selected);
             break;
         case IPL_TYPE_FLOPPY:
             map_floppy_drive(pos->drive);
-            add_bev(IPL_TYPE_FLOPPY, 0);
+            add_bev(IPL_TYPE_FLOPPY, 0, pos->selected);
             break;
         case IPL_TYPE_HARDDISK:
             map_hd_drive(pos->drive);
-            add_bev(IPL_TYPE_HARDDISK, 0);
+            add_bev(IPL_TYPE_HARDDISK, 0, pos->selected);
             break;
         case IPL_TYPE_CDROM:
             map_cd_drive(pos->drive);
             // NO BREAK
         default:
-            add_bev(pos->type, pos->data);
+		add_bev(pos->type, pos->data, pos->selected);
             break;
         }
         pos = pos->next;
     }
 
     // If nothing added a floppy/hd boot - add it manually.
-    add_bev(IPL_TYPE_FLOPPY, 0);
-    add_bev(IPL_TYPE_HARDDISK, 0);
+    add_bev(IPL_TYPE_FLOPPY, 0, 0);
+    add_bev(IPL_TYPE_HARDDISK, 0, 0);
 }
 
 
@@ -654,6 +665,12 @@ do_boot(int seq_nr)
 
     // Boot the given BEV type.
     struct bev_s *ie = &BEV[seq_nr];
+
+    int strict = romfile_loadint("etc/boot-strict", 0);
+    // do strict boot, only boot from user selected devices
+    if (strict && !ie->selected)
+        boot_fail();
+
     switch (ie->type) {
     case IPL_TYPE_FLOPPY:
         printf("Booting from Floppy...\n");
-- 
1.7.1