grub.cfg: bruteforce linux/initrd if no grub.cfg

this is probably not safe, and neither is the current
fall back code which is being removed from master.

i already finished it before testing, but after realising
the above, so i'll just stash it in this branch for now.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/grub/config/grub.cfg

@@ -90,6 +90,11 @@ function search_isolinux {
 	done
 	echo # Insert newline
 }
+
+function try_without_config {
+
+}
+
 menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o' {
 
 	if [ "${grub_scan_disk}" != "ata" ]; then
@@ -146,31 +151,104 @@ menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o
 		try_user_config "${vol}"
 	done
 
-	if [ "${grub_scan_disk}" != "ata" ]; then
-		# Last resort, if all else fails
-		set root=ahci0,1
-		for p in / /boot/; do
-			if [ -f "${p}vmlinuz" ]; then
-				linux ${p}vmlinuz root=/dev/sda1 rw
-				if [ -f "${p}initrd.img" ]; then
-					initrd ${p}initrd.img
+	# bruteforce as a last result. figure out how to boot
+	# linux without a grub configuration file. (crypto and lvm unsupported)
+	set vmlinuz=""
+	set initrd=""
+	set devtype=""
+	set devnum=""
+	set devletter=""
+	set partnum=""
+	for t in ata ahci; do
+		set vmlinuz=""
+		set initrd=""
+		if [ "${t}" = "ata" ] && [ "${grub_scan_disk}" = "ahci" ]; then
+			continue
+		elif [ "${t}" = "ahci" ] && [ "${grub_scan_disk}" = "ata" ]; then
+			continue
+		fi
+		for dev in 0 1 2 3 4 5 6 7 8; do
+			for part in 1 2 3 4 5 6 7 8 9; do
+				set root="${t}${devnum},${partnum}"
+				set devnum="${dev}"
+				set partnum="${part}"
+				for k in /vmlinuz* @/vmlinuz*; do
+					if [ ! -f "${k}" ] || [ ! -d /boot ]; then
+						continue
+					fi
+					set vmlinuz="${k}"
+					# do not break. if furthe rentries are
+					# available, due to alphabetic sorting,
+					# the next entry is likely a newer
+					# kernel version
+				done
+				for k in /boot/vmlinuz* @/boot/vmlinuz*; do
+					if [ "${vmlinuz}" != "" ]; then
+						break
+					fi
+					set vmlinuz="${k}"
+				done
+				if [ "${vmlinuz}" = "" ]; then
+					continue
 				fi
-			fi
-		done
-	fi
-
-	if [ "${grub_scan_disk}" != "ahci" ]; then
-		# Last resort (for setups that use IDE instead of SATA)
-		set root=ata0,1
-		for p in / /boot/; do
-			if [ -f "${p}vmlinuz" ]; then
-				linux ${p}vmlinuz root=/dev/sda1 rw
-				if [ -f "${p}initrd.img" ]; then
-					initrd ${p}initrd.img
+				for i in /initrd* /initramfs* @/initrd* @/initramfs*; do
+					if [ ! -f "${i}" ] || [ ! -d "/boot" ]; then
+						continue
+					done
+					set initrd="${i}"
+					# ditto. do not break yet
+				done
+				for i in /boot/initrd* /boot/initramfs* @/boot/initrd* @/boot/initramfs*; do
+					if [ "${initrd}" != "" ]; then
+						break
+					fi
+					set initrd="${i}"
+				done
+				if [ "${vmlinuz}" != "" ] && [ "${initrd}" != "" ]; then
+					set devtype="${t}"
+					break
 				fi
+				set vmlinuz=""
+				set initrd=""
+			done
+			if [ "${vmlinuz}" != "" ] && [ "${initrd}" != "" ]; then
+				break
 			fi
 		done
+		if [ "${vmlinuz}" != "" ] && [ "${initrd}" != "" ]; then
+			break
+		fi
+	done
+
+	if [ "${vmlinuz}" = "" ] || [ "${initrd}" = "" ]; then
+		return
+	fi
+	if [ "${devnum}" = "0" ]; then
+		set devletter="a"
+	elif [ "${devnum}" = "1" ]; then
+		set devletter="b"
+	elif [ "${devnum}" = "2" ]; then
+		set devletter="c"
+	elif [ "${devnum}" = "3" ]; then
+		set devletter="d"
+	elif [ "${devnum}" = "4" ]; then
+		set devletter="e"
+	elif [ "${devnum}" = "5" ]; then
+		set devletter="f"
+	elif [ "${devnum}" = "6" ]; then
+		set devletter="g"
+	elif [ "${devnum}" = "7" ]; then
+		set devletter="h"
+	elif [ "${devnum}" = "8" ]; then
+		set devletter="i"
+	fi
+	set btrfsvol=""
+	if [ "${vmlinuz#@}" != "${vmlinuz}" ]; then
+		set btrfsvol="rootflags=subvol=@"
 	fi
+	set root="${devtype}${devnum},${partnum}"
+	linux ${vmlinuz} root=/dev/sd${devletter}${partnum} ${btrfsvol} rw
+	initrd ${initrd}
 
 	true # Prevent pager requiring to accept each line instead of whole screen
 }