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Subject[PATCH 2/3] kbuild: handle module compression while running 'make modules_install'.
Date
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 used option -9 to get the maximum compression ratio. 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>
---
Makefile | 15 +++++++++++++++
init/Kconfig | 43 +++++++++++++++++++++++++++++++++++++++++++
scripts/Makefile.modinst | 3 ++-
3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index e432442..ba7873e 100644
--- a/Makefile
+++ b/Makefile
@@ -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 -9
+ endif # CONFIG_MODULE_COMPRESS_GZIP
+ ifdef CONFIG_MODULE_COMPRESS_XZ
+ mod_compress_cmd = xz -9
+ 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.
#
diff --git a/init/Kconfig b/init/Kconfig
index e84c642..4980925 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
index aa911b5..e48a4e9 100644
--- a/scripts/Makefile.modinst
+++ b/scripts/Makefile.modinst
@@ -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
--
2.0.4


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