Commit beb50df3 authored by Bertrand Jacquin's avatar Bertrand Jacquin Committed by Rusty Russell
Browse files

kbuild: handle module compression while running 'make modules_install'. 



Since module-init-tools (gzip) and kmod (gzip and xz) support compressed
modules, it could be useful to include a support for compressing modules
right after having them installed. Doing this in kbuild instead of per
distro can permit to make this kind of usage more generic.

This patch add a Kconfig entry to "Enable loadable module support" menu
and let you choose to compress using gzip (default) or xz.

Both gzip and xz does not used any extra -[1-9] option since Andi Kleen
and Rusty Russell prove no gain is made using them. gzip is called with -n
argument to avoid storing original filename inside compressed file, that
way we can save some more bytes.

On a v3.16 kernel, 'make allmodconfig' generated 4680 modules for a
total of 378MB (no strip, no sign, no compress), the following table
shows observed disk space gain based on the allmodconfig .config :

       |           time                |
       +-------------+-----------------+
       | manual .ko  |       make      | size | percent
       | compression | modules_install |      | gain
       +-------------+-----------------+------+--------
  -    |             |     18.61s      | 378M |
  GZIP |   3m16s     |     3m37s       | 102M | 73.41%
  XZ   |   5m22s     |     5m39s       |  77M | 79.83%

The gain for restricted environnement seems to be interesting while
uncompress can be time consuming but happens only while loading a module,
that is generally done only once.

This is fully compatible with signed modules while the signed module is
compressed. module-init-tools or kmod handles decompression
and provide to other layer the uncompressed but signed payload.

Reviewed-by: default avatarWilly Tarreau <w@1wt.eu>
Signed-off-by: default avatarBertrand Jacquin <beber@meleeweb.net>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 40e42f6a

Makefile

+15 −0
Original line number Diff line number Diff line
@@ -842,6 +842,21 @@ mod_strip_cmd = true 
endif # INSTALL_MOD_STRIP

export mod_strip_cmd



# CONFIG_MODULE_COMPRESS, if defined, will cause module to be compressed

# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP

# or CONFIG_MODULE_COMPRESS_XZ.



mod_compress_cmd = true

ifdef CONFIG_MODULE_COMPRESS

  ifdef CONFIG_MODULE_COMPRESS_GZIP

    mod_compress_cmd = gzip -n

  endif # CONFIG_MODULE_COMPRESS_GZIP

  ifdef CONFIG_MODULE_COMPRESS_XZ

    mod_compress_cmd = xz

  endif # CONFIG_MODULE_COMPRESS_XZ

endif # CONFIG_MODULE_COMPRESS

export mod_compress_cmd



# Select initial ramdisk compression format, default is gzip(1).

# This shall be used by the dracut(8) tool while creating an initramfs image.

#

init/Kconfig

+43 −0
Original line number Diff line number Diff line
@@ -1906,6 +1906,49 @@ config MODULE_SIG_HASH 
	default "sha384" if MODULE_SIG_SHA384

	default "sha512" if MODULE_SIG_SHA512



config MODULE_COMPRESS

	bool "Compress modules on installation"

	depends on MODULES

	help

	  This option compresses the kernel modules when 'make

	  modules_install' is run.



	  The modules will be compressed either using gzip or xz depend on the

	  choice made in "Compression algorithm".



	  module-init-tools has support for gzip format while kmod handle gzip

	  and xz compressed modules.



	  When a kernel module is installed from outside of the main kernel

	  source and uses the Kbuild system for installing modules then that

	  kernel module will also be compressed when it is installed.



	  This option provides little benefit when the modules are to be used inside

	  an initrd or initramfs, it generally is more efficient to compress the whole

	  initrd or initramfs instead.



	  This is fully compatible with signed modules while the signed module is

	  compressed. module-init-tools or kmod handles decompression and provide to

	  other layer the uncompressed but signed payload.



choice

	prompt "Compression algorithm"

	depends on MODULE_COMPRESS

	default MODULE_COMPRESS_GZIP

	help

	  This determines which sort of compression will be used during

	  'make modules_install'.



	  GZIP (default) and XZ are supported.



config MODULE_COMPRESS_GZIP

	bool "GZIP"



config MODULE_COMPRESS_XZ

	bool "XZ"



endchoice



endif # MODULES



config INIT_ALL_POSSIBLE

scripts/Makefile.modinst

+2 −1
Original line number Diff line number Diff line
@@ -22,7 +22,8 @@ quiet_cmd_modules_install = INSTALL $@ 
    mkdir -p $(2) ; \

    cp $@ $(2) ; \

    $(mod_strip_cmd) $(2)/$(notdir $@) ; \

    $(mod_sign_cmd) $(2)/$(notdir $@) $(patsubst %,|| true,$(KBUILD_EXTMOD))

    $(mod_sign_cmd) $(2)/$(notdir $@) $(patsubst %,|| true,$(KBUILD_EXTMOD)) ; \

    $(mod_compress_cmd) $(2)/$(notdir $@)



# Modules built outside the kernel source tree go into extra by default

INSTALL_MOD_DIR ?= extra

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