initrd/bin/unpack_initramfs.sh: add xz to unpack logic (add commented: bzip2, lzma, lzo and lz4)

xz: tested working with tails test build and 6.8.1's initrd
latest ubuntu 24.10: switched back to zstd, works as expected (tested)

Magic numbers referred at:
- 28eb75e178/scripts/extract-vmlinux (L52C1-L58C43)
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/decompress.c#n51

Signed-off-by: Thierry Laurion <insurgo@riseup.net>

initrd/bin/unpack_initramfs.sh

@@ -90,6 +90,10 @@ unpack_first_segment() {
 			# walking all the compressed blocks.
 			gunzip | unpack_cpio
 			;;
+		fd37*) # xz
+			DEBUG "archive segment $magic: xz"
+			unxz | unpack_cpio
+			;;
 		28b5*) # zstd
 			DEBUG "archive segment $magic: zstd"
 			# Like gunzip, this will not stop when reaching the end of the
@@ -99,6 +103,26 @@ unpack_first_segment() {
 			;;
 		*) # unknown
 			die "Can't decompress initramfs archive, unknown type: $magic"
+			# The following are magic values for other compression formats
+			#  but not added because not tested.
+			# TODO: open an issue for unsupported magic number reported on die.
+			# 
+			#425a*) # bzip2
+			#	DEBUG "archive segment $magic: bzip2"
+			#	bunzip2 | unpack_cpio
+			#;;
+			#5d00*) # lzma
+			#	DEBUG "archive segment $magic: lzma"
+			#	unlzma | unpack_cpio
+			#;;
+			#894c*) # lzo
+			#	DEBUG "archive segment $magic: lzo"
+			#	lzop -d | unpack_cpio
+			#;;
+			#0221*) # lz4
+			#	DEBUG "archive segment $magic: lz4"
+			#	lz4 -d | unpack_cpio
+			#	;;
 			;;
 		esac
 	) <"$unpack_archive" >"$rest_archive"