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

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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: Willy Tarreau <w@1wt.eu>
Signed-off-by: Bertrand Jacquin <beber@meleeweb.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Bertrand Jacquin 2014-08-27 20:31:56 +09:30 committed by Rusty Russell
parent 40e42f6a25
commit beb50df39e
3 changed files with 60 additions and 1 deletions
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15
Makefile
View file

@ -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.
#

43
init/Kconfig
View file

@ -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

3
scripts/Makefile.modinst
View file

@ -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