initramfs: read CONFIG_RD_ variables for initramfs compression

When expert configuration option(CONFIG_EXPERT) is enabled, menuconfig
offers a choice of compression algorithm to compress initial ramfs image;
This choice is stored into CONFIG_RD_* variables. But usr/Makefile uses
earlier INITRAMFS_COMPRESSION_* macros to build initial ramfs file. Since
none of them is defined, resulting 'initramfs_data.cpio' file remains
un-compressed.

This patch updates the Makefile to use CONFIG_RD_* variables and adds
support for LZ4 compression algorithm. Also updates the
'gen_initramfs_list.sh' script to check whether a selected compression
command is accessible or not. And fall-back to default gzip(1)
compression when it is not.

Signed-off-by: P J P <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/gen_initramfs_list.sh

···
 		output_file="$1"
 		cpio_list="$(mktemp ${TMPDIR:-/tmp}/cpiolist.XXXXXX)"
 		output=${cpio_list}
-		echo "$output_file" | grep -q "\.gz$" && compr="gzip -n -9 -f"
-		echo "$output_file" | grep -q "\.bz2$" && compr="bzip2 -9 -f"
-		echo "$output_file" | grep -q "\.lzma$" && compr="lzma -9 -f"
-		echo "$output_file" | grep -q "\.xz$" && \
-				compr="xz --check=crc32 --lzma2=dict=1MiB"
-		echo "$output_file" | grep -q "\.lzo$" && compr="lzop -9 -f"
+		echo "$output_file" | grep -q "\.gz$" \
+                && [ -x "`which gzip 2> /dev/null`" ] \
+                && compr="gzip -n -9 -f"
+		echo "$output_file" | grep -q "\.bz2$" \
+                && [ -x "`which bzip2 2> /dev/null`" ] \
+                && compr="bzip2 -9 -f"
+		echo "$output_file" | grep -q "\.lzma$" \
+                && [ -x "`which lzma 2> /dev/null`" ] \
+                && compr="lzma -9 -f"
+		echo "$output_file" | grep -q "\.xz$" \
+                && [ -x "`which xz 2> /dev/null`" ] \
+                && compr="xz --check=crc32 --lzma2=dict=1MiB"
+		echo "$output_file" | grep -q "\.lzo$" \
+                && [ -x "`which lzop 2> /dev/null`" ] \
+                && compr="lzop -9 -f"
+		echo "$output_file" | grep -q "\.lz4$" \
+                && [ -x "`which lz4 2> /dev/null`" ] \
+                && compr="lz4 -9 -f"
 		echo "$output_file" | grep -q "\.cpio$" && compr="cat"
 		shift
 		;;

usr/Makefile

···
 PHONY += klibcdirs
 
 
-# Gzip
-suffix_$(CONFIG_INITRAMFS_COMPRESSION_GZIP)   = .gz
-
 # Bzip2
-suffix_$(CONFIG_INITRAMFS_COMPRESSION_BZIP2)  = .bz2
+suffix_$(CONFIG_RD_BZIP2)  = .bz2
 
 # Lzma
-suffix_$(CONFIG_INITRAMFS_COMPRESSION_LZMA)   = .lzma
+suffix_$(CONFIG_RD_LZMA)   = .lzma
 
 # XZ
-suffix_$(CONFIG_INITRAMFS_COMPRESSION_XZ)     = .xz
+suffix_$(CONFIG_RD_XZ)     = .xz
 
 # Lzo
-suffix_$(CONFIG_INITRAMFS_COMPRESSION_LZO)   = .lzo
+suffix_$(CONFIG_RD_LZO)    = .lzo
+
+# Lz4
+suffix_$(CONFIG_RD_LZ4)    = .lz4
+
+# Gzip
+suffix_$(CONFIG_RD_GZIP)   = .gz
 
 AFLAGS_initramfs_data.o += -DINITRAMFS_IMAGE="usr/initramfs_data.cpio$(suffix_y)"
 
···
 quiet_cmd_initfs = GEN     $@
       cmd_initfs = $(initramfs) -o $@ $(ramfs-args) $(ramfs-input)
 
-targets := initramfs_data.cpio.gz initramfs_data.cpio.bz2 initramfs_data.cpio.lzma initramfs_data.cpio.xz initramfs_data.cpio.lzo initramfs_data.cpio
+targets := initramfs_data.cpio.gz initramfs_data.cpio.bz2 \
+	initramfs_data.cpio.lzma initramfs_data.cpio.xz \
+	initramfs_data.cpio.lzo initramfs_data.cpio.lz4 \
+	initramfs_data.cpio
 # do not try to update files included in initramfs
 $(deps_initramfs): ;
 
···
 $(obj)/initramfs_data.cpio$(suffix_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
 	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/.initramfs_data.cpio.d
 	$(call if_changed,initfs)
-