configs/*/grub/grub.cfg: search for a .uuid file in /.disk/ and use the volume it's on

Search for `/.disk/%UUID_SEARCH_FILENAME%.uuid` and pass the UUID of the
volume it's on as `archisodevice`. mkarchiso will replace
`%UUID_SEARCH_FILENAME%` with a hardcoded value generated using
`SOURCE_DATE_EPOCH` durring ISO build.

This allows to prepare an UEFI bootable installation medium by simply
copying the directory structure without having to touch `grub.cfg`.

Relying on the volume UUID instead of its LABEL also avoids collisions
of multiple ISOs created in the same month.

Fixes #202

3 files changed, 20 insertions, 9 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 66ffe75..f6a6f25 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,9 +8,16 @@ Changelog
 Added
 -----
 
+- Support *file system transposition* to simplify boot medium preparation for UEFI boot via extracting the ISO image
+  contents to a drive. ``grub.cfg`` does not hardcode the ISO volume label anymore, instead GRUB will search for volume
+  with a ``/.disk/%UUID_SEARCH_FILENAME%.uuid`` file on it.
+
 Changed
 -------
 
+- Identify the ISO volume via a UUID instead of a file system label to avoid collisions of multiple ISOs created in the
+  same month.
+
 Removed
 -------
 
diff --git a/configs/baseline/grub/grub.cfg b/configs/baseline/grub/grub.cfg
index d2aa4ab..7d73fe6 100644
--- a/configs/baseline/grub/grub.cfg
+++ b/configs/baseline/grub/grub.cfg
@@ -20,6 +20,11 @@ if serial --unit=0 --speed=115200; then
     terminal_output --append serial
 fi
 
+# Search for the ISO volume
+regexp --set=1:ARCHISO_HINT '^\(([^)]+)\)' "${cmdpath}"
+search --no-floppy --set=root --file '/.disk/%UUID_SEARCH_FILENAME%.uuid' --hint "${ARCHISO_HINT}"
+probe --set ARCHISO_UUID --fs-uuid "${root}"
+
 # Set default menu entry
 default=archlinux
 timeout=15
@@ -30,7 +35,6 @@ timeout_style=menu
 
 menuentry "Arch Linux (x86_64, UEFI)" --class arch --class gnu-linux --class gnu --class os --id 'archlinux' {
     set gfxpayload=keep
-    search --no-floppy --set=root --label %ARCHISO_LABEL%
-    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisolabel=%ARCHISO_LABEL%
+    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisodevice=/dev/disk/by-uuid/${ARCHISO_UUID}
     initrd /%INSTALL_DIR%/boot/x86_64/initramfs-linux.img
 }
diff --git a/configs/releng/grub/grub.cfg b/configs/releng/grub/grub.cfg
index 79ea2d2..ddd8af2 100644
--- a/configs/releng/grub/grub.cfg
+++ b/configs/releng/grub/grub.cfg
@@ -20,6 +20,11 @@ if serial --unit=0 --speed=115200; then
     terminal_output --append serial
 fi
 
+# Search for the ISO volume
+regexp --set=1:ARCHISO_HINT '^\(([^)]+)\)' "${cmdpath}"
+search --no-floppy --set=root --file '/.disk/%UUID_SEARCH_FILENAME%.uuid' --hint "${ARCHISO_HINT}"
+probe --set ARCHISO_UUID --fs-uuid "${root}"
+
 # Set default menu entry
 default=archlinux
 timeout=15
@@ -32,15 +37,13 @@ play 600 988 1 1319 4
 
 menuentry "Arch Linux install medium (x86_64, UEFI)" --class arch --class gnu-linux --class gnu --class os --id 'archlinux' {
     set gfxpayload=keep
-    search --no-floppy --set=root --label %ARCHISO_LABEL%
-    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisolabel=%ARCHISO_LABEL%
+    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisodevice=/dev/disk/by-uuid/${ARCHISO_UUID}
     initrd /%INSTALL_DIR%/boot/intel-ucode.img /%INSTALL_DIR%/boot/amd-ucode.img /%INSTALL_DIR%/boot/x86_64/initramfs-linux.img
 }
 
 menuentry "Arch Linux install medium with speakup screen reader (x86_64, UEFI)" --hotkey s --class arch --class gnu-linux --class gnu --class os --id 'archlinux-accessibility' {
     set gfxpayload=keep
-    search --no-floppy --set=root --label %ARCHISO_LABEL%
-    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisolabel=%ARCHISO_LABEL% accessibility=on
+    linux /%INSTALL_DIR%/boot/x86_64/vmlinuz-linux archisobasedir=%INSTALL_DIR% archisodevice=/dev/disk/by-uuid/${ARCHISO_UUID} accessibility=on
     initrd /%INSTALL_DIR%/boot/intel-ucode.img /%INSTALL_DIR%/boot/amd-ucode.img /%INSTALL_DIR%/boot/x86_64/initramfs-linux.img
 }
 
@@ -48,18 +51,15 @@ if [ "${grub_platform}" == "efi" ]; then
     if [ "${grub_cpu}" == "x86_64" ]; then
         menuentry "Run Memtest86+ (RAM test)" --class memtest86 --class gnu --class tool {
             set gfxpayload=800x600,1024x768
-            search --fs-uuid --no-floppy --set=root --label %ARCHISO_LABEL%
             linux /%INSTALL_DIR%/boot/memtest.efi
         }
         menuentry "UEFI Shell" {
             insmod chain
-            search --no-floppy --set=root --label %ARCHISO_LABEL%
             chainloader /shellx64.efi
         }
     elif [ "${grub_cpu}" == "i386" ]; then
         menuentry "UEFI Shell" {
             insmod chain
-            search --no-floppy --set=root --label %ARCHISO_LABEL%
             chainloader /shellia32.efi
         }
     fi