Add GRUB_BTRFS_LIMIT

Allow user to limit the number of snapshots listed in GRUB. This also reverses
the order of the snapshots such that the more recent ones come first. That is,
if a user specifies GRUB_BTRFS_LIMIT=10, then only the 10 most recent snapshots
will be shown. The default limit is 100, which seems very large. The more
snapshots in the GRUB menu, the longer the system takes to boot.

41_snapshots-btrfs

@@ -72,6 +72,11 @@ nkernel=("${GRUB_BTRFS_NKERNEL[@]}")
 ninit=("${GRUB_BTRFS_NINIT[@]}")
 ## Microcode(s) name(s)
 microcode=("${GRUB_BTRFS_INTEL_UCODE[@]}")
+## Limit to show in menu
+limit=("${GRUB_BTRFS_LIMIT[@]}")
+if [ -z "$limit" ]; then
+    limit=100
+fi
 
 ########################
 ### variables script ###
@@ -156,7 +161,7 @@ snapshots_entry()
 ## List of snapshots on filesystem
 snapshot_list()
 {
-	for snap in $(btrfs subvolume list -sa /); do
+	for snap in $(btrfs subvolume list -sa / | tac); do
 		IFS=$oldIFS
 		snap=($snap)
 		local snap_path_name=${snap[@]:13:${#snap[@]}}
@@ -249,6 +254,7 @@ title_format()
 list_kernels_initramfs()
 {
 	IFS=$'\n'
+    c=0
 	for item in $(snapshot_list); do
 		IFS=$oldIFS
 		item=($item)
@@ -276,6 +282,10 @@ list_kernels_initramfs()
 		title_format
 		# echo "${title_menu[*]}"
 		snapshots_entry
+        c=$((1+$c))
+        if [[ $c -gt $limit ]]; then
+            break;
+        fi
 	done
 	IFS=$oldIFS
 }
@@ -292,4 +302,4 @@ if [ ${choise_of_method} = "1" ] ; then
 	umount $gbgmp
 	gettext_printf "###### - Grub-btrfs: Auto-detect - ######\n" >&2 ;
 fi
-### End choice of method ###
+### End choice of method ###