[PATCH] create option to compress initramfs within the kernel

[PATCH] create option to compress initramfs within the kernel

[frans]

Below is a patch to make compression of the initramfs image optional.
Sumbitted to LKML as there is no MAINTAINER listed for initramfs.

Rationale is that if you create a compressed kernel image (e.g. by
make bzImage) it is not very efficient and useful to compress initramfs 
as the initramfs will be compressed anyway when the kernel image is 
compressed.

The patch below allows one to select whether compression is desired or not 
using a new boolean Kconfig option (INITRAMFS_COMPRESS). Default value: y

As the .cpio.gz extension of the generated initramfs.cpio.gz is also a 
little bit odd if you have no compression, the name of the initramfs image 
has been changed from initramfs.cpio.gz to initramfs.img

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>

diff --git a/scripts/gen_initramfs_list.sh b/scripts/gen_initramfs_list.sh
index 5f3415f..22f71ee 100644
--- a/scripts/gen_initramfs_list.sh
+++ b/scripts/gen_initramfs_list.sh
@@ -185,7 +185,7 @@ dir_filelist() {
 }

 # if only one file is specified and it is .cpio file then use it direct as fs
-# if a directory is specified then add all files in given direcotry to fs
+# if a directory is specified then add all files in given directory to fs
 # if a regular file is specified assume it is in gen_initramfs format
 input_file() {
 	source="$1"
@@ -225,6 +225,7 @@ cpio_list=
 output="/dev/stdout"
 output_file=""
 is_cpio_compressed=
+compress=0

 arg="$1"
 case "$arg" in
@@ -257,6 +258,9 @@ while [ $# -gt 0 ]; do
 			default_list="$arg"
 			${dep_list}default_initramfs
 			;;
+		"-c")	# compress
+			compress=1
+			;;
 		"-h")
 			usage
 			exit 0
@@ -287,7 +291,11 @@ if [ ! -z ${output_file} ]; then
 	if [ "${is_cpio_compressed}" = "compressed" ]; then
 		cat ${cpio_tfile} > ${output_file}
 	else
-		cat ${cpio_tfile} | gzip -f -9 - > ${output_file}
+		if [ ${compress} -eq 1 ]; then
+			cat ${cpio_tfile} | gzip -f -9 - > ${output_file}
+		else
+			cat ${cpio_tfile} > ${output_file}
+		fi
 	fi
 	[ -z ${cpio_file} ] && rm ${cpio_tfile}
 fi
diff --git a/usr/Kconfig b/usr/Kconfig
index 86cecb5..7f78577 100644
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -44,3 +44,14 @@ config INITRAMFS_ROOT_GID
 	  owned by group root in the initial ramdisk image.

 	  If you are not sure, leave it set to "0".
+
+config INITRAMFS_COMPRESS
+	bool "Compress initramfs image"
+	default y
+	help
+	  If you want a compressed initramfs image in your kernel say y
+	  If you do not want your initramfs image to be compressed say n. 
+	  A compressed initramfs is generally not useful if you also have a
+	  compressed kernel (vmlinuz, bzImage).
+
+	  If you are not sure, levae it to y.
diff --git a/usr/Makefile b/usr/Makefile
index 201f27f..6609896 100644
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -9,10 +9,10 @@ PHONY += klibcdirs
 # Generate builtin.o based on initramfs_data.o
 obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o

-# initramfs_data.o contains the initramfs_data.cpio.gz image.
+# initramfs_data.o contains the initramfs_data.img image.
 # The image is included using .incbin, a dependency which is not
 # tracked automatically.
-$(obj)/initramfs_data.o: $(obj)/initramfs_data.cpio.gz FORCE
+$(obj)/initramfs_data.o: $(obj)/initramfs_data.img FORCE

 #####
 # Generate the initramfs cpio archive
@@ -23,30 +23,31 @@ ramfs-input := $(if $(filter-out "",$(CONFIG_INITRAMFS_SOURCE)), \
 			$(shell echo $(CONFIG_INITRAMFS_SOURCE)),-d)
 ramfs-args  := \
         $(if $(CONFIG_INITRAMFS_ROOT_UID), -u $(CONFIG_INITRAMFS_ROOT_UID)) \
-        $(if $(CONFIG_INITRAMFS_ROOT_GID), -g $(CONFIG_INITRAMFS_ROOT_GID))
+        $(if $(CONFIG_INITRAMFS_ROOT_GID), -g $(CONFIG_INITRAMFS_ROOT_GID)) \
+        $(if $(CONFIG_INITRAMFS_COMPRESS), -c )

-# .initramfs_data.cpio.gz.d is used to identify all files included
+# .initramfs_data.img.d is used to identify all files included
 # in initramfs and to detect if any files are added/removed.
 # Removed files are identified by directory timestamp being updated
 # The dependency list is generated by gen_initramfs.sh -l
-ifneq ($(wildcard $(obj)/.initramfs_data.cpio.gz.d),)
-	include $(obj)/.initramfs_data.cpio.gz.d
+ifneq ($(wildcard $(obj)/.initramfs_data.img.d),)
+	include $(obj)/.initramfs_data.img.d
 endif

 quiet_cmd_initfs = GEN     $@
       cmd_initfs = $(initramfs) -o $@ $(ramfs-args) $(ramfs-input)

-targets := initramfs_data.cpio.gz
+targets := initramfs_data.img
 # do not try to update files included in initramfs
 $(deps_initramfs): ;

 $(deps_initramfs): klibcdirs
-# We rebuild initramfs_data.cpio.gz if:
-# 1) Any included file is newer then initramfs_data.cpio.gz
+# We rebuild initramfs_data.img if:
+# 1) Any included file is newer then initramfs_data.img
 # 2) There are changes in which files are included (added or deleted)
-# 3) If gen_init_cpio are newer than initramfs_data.cpio.gz
+# 3) If gen_init_cpio are newer than initramfs_data.img
 # 4) arguments to gen_initramfs.sh changes
-$(obj)/initramfs_data.cpio.gz: $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
-	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/.initramfs_data.cpio.gz.d
+$(obj)/initramfs_data.img: $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
+	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/.initramfs_data.img.d
 	$(call if_changed,initfs)

diff --git a/usr/initramfs_data.S b/usr/initramfs_data.S
index c2e1ad4..5820d65 100644
--- a/usr/initramfs_data.S
+++ b/usr/initramfs_data.S
@@ -8,7 +8,7 @@


   ld -m elf_i386  --format binary --oformat elf32-i386 -r \
-  -T initramfs_data.scr initramfs_data.cpio.gz -o initramfs_data.o
+  -T initramfs_data.scr initramfs_data.img -o initramfs_data.o
    ld -m elf_i386  -r -o built-in.o initramfs_data.o

   initramfs_data.scr looks like this:
@@ -26,5 +26,5 @@ SECTIONS
 */

 .section .init.ramfs,"a"
-.incbin "usr/initramfs_data.cpio.gz"
+.incbin "usr/initramfs_data.img"

Re: [PATCH] create option to compress initramfs within the kernel

[Rob Landley]

On Saturday 22 November 2008 11:30:13 frans wrote:
> Below is a patch to make compression of the initramfs image optional.
> Sumbitted to LKML as there is no MAINTAINER listed for initramfs.
>
> Rationale is that if you create a compressed kernel image (e.g. by
> make bzImage) it is not very efficient and useful to compress initramfs
> as the initramfs will be compressed anyway when the kernel image is
> compressed.

Actually it saves intermediate space (the cpio archive and the decompressed 
ramfs coexist during the decompression, until the kernel can free the cpio 
archive), so it does serve a purpose.  (Given cache effects leaving it 
compressed may actually wind up being faster on modern CPUs because it dirties 
fewer pages.)

It also eats CPU, which is at more of a premium than memory on some little 
battery powered wind-up boxes.  But I'd be happier seeing some actual 
benchmark numbers on a device that would actually _notice_ this change.

> @@ -257,6 +258,9 @@ while [ $# -gt 0 ]; do
>  			default_list="$arg"
>  			${dep_list}default_initramfs
>  			;;
> +		"-c")	# compress
> +			compress=1
> +			;;

You're changing the default behavior for people who run this script directly.  
Just FYI.

> --- a/usr/Kconfig
> +++ b/usr/Kconfig
> @@ -44,3 +44,14 @@ config INITRAMFS_ROOT_GID
>  	  owned by group root in the initial ramdisk image.
>
>  	  If you are not sure, leave it set to "0".
> +
> +config INITRAMFS_COMPRESS
> +	bool "Compress initramfs image"
> +	default y
> +	help
> +	  If you want a compressed initramfs image in your kernel say y
> +	  If you do not want your initramfs image to be compressed say n.
> +	  A compressed initramfs is generally not useful if you also have a
> +	  compressed kernel (vmlinuz, bzImage).

This should probably be in the CONFIG_EMBEDDED menu.

Rob

Re: [PATCH] create option to compress initramfs within the kernel

[Frans Meulenbroeks]

Dang. Did a reply instead of a reply all. Here it is again now also to
lkml and dwmw2.

2008/11/23 Rob Landley <rob@landley.net>:

>> Rationale is that if you create a compressed kernel image (e.g. by
>> make bzImage) it is not very efficient and useful to compress initramfs
>> as the initramfs will be compressed anyway when the kernel image is
>> compressed.
>
> Actually it saves intermediate space (the cpio archive and the decompressed
> ramfs coexist during the decompression, until the kernel can free the cpio
> archive), so it does serve a purpose.  (Given cache effects leaving it
> compressed may actually wind up being faster on modern CPUs because it dirties
> fewer pages.)
>
> It also eats CPU, which is at more of a premium than memory on some little
> battery powered wind-up boxes.  But I'd be happier seeing some actual
> benchmark numbers on a device that would actually _notice_ this change.

I agree that a compressed initramfs image saves intermediate RAM
space. If one cannot afford to use this temporary space, then a
compressed initramfs is definitely better.
Double compression definitely eats CPU. I did not bench the
compression part alone.but I'll try to find some time to bench it in
more detail. Of course it also depends on the size of the initramfs.
For a 300k initramfs this is not going to make much of a difference.
However we once turned our 20MB or so squashfs image into initramfs
and it took about 1.5 seconds to decompress and populate the buffer
cache. (20MB is compressed, uncomressed it is around 50M) (I do not
have exact figures handy, but this is what I recall). CPU is a 180 Mhz
or so MIPS.

>
>> @@ -257,6 +258,9 @@ while [ $# -gt 0 ]; do
>>                       default_list="$arg"
>>                       ${dep_list}default_initramfs
>>                       ;;
>> +             "-c")   # compress
>> +                     compress=1
>> +                     ;;
>
> You're changing the default behavior for people who run this script directly.
> Just FYI.

Do they exist? Actually I went for -c because it is mnemonically easy
to say that c is for compress. If there are better suggestions for an
option that does not compress,. I am more than happy to change things.
(I don't really like things like -n for nocompress).;

>
>> --- a/usr/Kconfig
>> +++ b/usr/Kconfig
>> @@ -44,3 +44,14 @@ config INITRAMFS_ROOT_GID
>>         owned by group root in the initial ramdisk image.
>>
>>         If you are not sure, leave it set to "0".
>> +
>> +config INITRAMFS_COMPRESS
>> +     bool "Compress initramfs image"
>> +     default y
>> +     help
>> +       If you want a compressed initramfs image in your kernel say y
>> +       If you do not want your initramfs image to be compressed say n.
>> +       A compressed initramfs is generally not useful if you also have a
>> +       compressed kernel (vmlinuz, bzImage).
>
> This should probably be in the CONFIG_EMBEDDED menu.

Can be done, but to me it felt it would be better to keep things
together, hence I added to usr/Kconfig.
Is there a policy on this? David, as embedded maintainer, do you have
an opinion?

Thanks for your feedback! Frans.