From b0f9dcabe96e5689ecfba9b6abcd27e685eabd48 Mon Sep 17 00:00:00 2001
From: Michael Chang <[email protected]>
Date: Wed, 11 May 2022 09:56:11 -0400
Subject: [PATCH] ofdisk: improve boot time by lookup boot disk first

While booting lvm, grub will try to build up logical volumes via hooks
to disk iteration where on-disk metadata can be read and parsed. However
the process can become very slow on multipath as reachable disks are
duplicated by multiple I/O paths and they all get inspected.

Fortunately grub allows lvm to be lazy binding and opportunistic that
root volume can be created when it's needed using a smaller set of
discovered disks. The disk iteration can also be controlled by pull
methods to only returning specified disks. That said we may be able to
take advantage of existing design to cause less overhead in lvm
construction.

This patch will return boot disks in OpenFirmware so they can be used
first. If lvm managed to create root volume out of those boot disks then
it is all very nice as they are readily available. Otherwise disk
scanning will be performed to present all discoverable disks to grub as
what it was done in the past. The result maybe again time consuming but
we have nothing to lose here.

Signed-off-by: Michael Chang <[email protected]>
---
 grub-core/disk/ieee1275/ofdisk.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/grub-core/disk/ieee1275/ofdisk.c
+++ b/grub-core/disk/ieee1275/ofdisk.c
@@ -491,10 +491,11 @@
 {
   unsigned i;
 
-  if (pull != GRUB_DISK_PULL_NONE)
+  if (pull > GRUB_DISK_PULL_REMOVABLE)
     return 0;
 
-  scan ();
+  if (pull == GRUB_DISK_PULL_REMOVABLE)
+    scan ();
 
   for (i = 0; i < ARRAY_SIZE (ofdisk_hash); i++)
     {
@@ -532,6 +533,12 @@
 	  if (!ent->is_boot && ent->is_removable)
 	    continue;
 
+	  if (pull == GRUB_DISK_PULL_NONE && !ent->is_boot)
+	    continue;
+
+	  if (pull == GRUB_DISK_PULL_REMOVABLE && ent->is_boot)
+	    continue;
+
 	  if (hook (ent->grub_shortest, hook_data))
 	    return 1;
 	}