linux: Fix initramfs compression
PATCH 1/1 linux: Fix initramfs compression
Initramfs compression does not make much sense for the architectures that support compressed kernel images because in this case the data would be compressed twice. This will eventually result in a bigger kernel image and time overhead when uncompressing it.
The only reason to use initramfs compression is to reduce memory usage when the kernel prepares initramfs, and both the unpacked filesystem and initramfs.cpio are present in the memory.
Buildroot attempts to force GZIP compression for initramfs, however it doesn't always work because initramfs compression mode depends on RAM disk compression supported by the kernel. Thus, CONFIG_INITRAMFS_COMPRESSION_GZIP depends on CONFIG_RD_GZIP. If CONFIG_RD_GZIP is not set, setting GZIP initramfs compression will have no effect.
Besides, the kernel also supports other compression methods, like BZIP2, LZMA, XZ and LZO. Forcing the good old GZIP does not really make much sense any more.
This attempts to find the first RAM disk compression mode supported by the kernel, parsing CONFIG_RD_... variables, and sets CONFIG_INITRAMFS_COMPRESSION_ accordingly. If no RAM disk compression is supported, no initramfs compression is set, and the kernel will use CONFIG_INITRAMFS_COMPRESSION_NONE.
I've slightly changed the KCONFIG_[SET|ENABLE|DISABLE]_OPT functions to be able to call them from shell "if" statement.
--- fs/initramfs/Config.in | 5 +++-- linux/linux.mk | 9 +++++++-- package/pkg-utils.mk | 6 +++--- 3 files changed, 13 insertions(+), 7 deletions(-)
fs/initramfs/Config.in +3 -2
@@ -9,8 +9,9 @@ config BR2_TARGET_ROOTFS_INITRAMFS A rootfs.cpio file will be generated in the images/ directory. This is the archive that will be included in the kernel image. - The rootfs in the kernel will always be gzip'ed, regardless - of how buildroot's cpio archive is configured. + The rootfs compression in the kernel will be set according to + the initial ram disk compression mode (CONFIG_RD_...) enabled, + regardless of how buildroot's cpio archive is configured. Note that enabling initramfs together with another filesystem formats doesn't make sense: you would end up having two
linux/linux.mk +7 -2
@@ -170,8 +170,13 @@ define LINUX_CONFIGURE_CMDS $(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_SOURCE,\"$(BINARIES_DIR)/rootfs.cpio\",$(@D)/.config) $(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_ROOT_UID,0,$(@D)/.config) $(call KCONFIG_SET_OPT,CONFIG_INITRAMFS_ROOT_GID,0,$(@D)/.config) - $(call KCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config) - $(call KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_GZIP,$(@D)/.config)) + for c in GZIP BZIP2 LZMA XZ LZO; do \ + if grep -qm1 "CONFIG_RD_$$c=y" $(@D)/.config; then \ + $(call KCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config); \ + $(call KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_$$c,$(@D)/.config); \ + break; \ + fi; \ + done) $(if $(BR2_ROOTFS_DEVICE_CREATION_STATIC),, $(call KCONFIG_ENABLE_OPT,CONFIG_DEVTMPFS,$(@D)/.config) $(call KCONFIG_ENABLE_OPT,CONFIG_DEVTMPFS_MOUNT,$(@D)/.config))
package/pkg-utils.mk +3 -3
@@ -30,17 +30,17 @@ UPPERCASE = $(strip $(eval __tmp := $1) \ # define KCONFIG_ENABLE_OPT - $(SED) "/\\<$(1)\\>/d" $(2) + $(SED) "/\\<$(1)\\>/d" $(2); \ echo "$(1)=y" >> $(2) endef define KCONFIG_SET_OPT - $(SED) "/\\<$(1)\\>/d" $(3) + $(SED) "/\\<$(1)\\>/d" $(3); \ echo "$(1)=$(2)" >> $(3) endef define KCONFIG_DISABLE_OPT - $(SED) "/\\<$(1)\\>/d" $(2) + $(SED) "/\\<$(1)\\>/d" $(2); \ echo "# $(1) is not set" >> $(2) endef
Signature · 1 line
1.7.11.4
PATCH 1/1 linux: Fix initramfs compression
linux/linux.mk define LINUX_CONFIGURE_CMDS · line 179
Quoted 9 lines · Valentine Barshak
linux/linux.mk +7
-2- $(call KCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config) - $(call KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_GZIP,$(@D)/.config)) + for c in GZIP BZIP2 LZMA XZ LZO; do \ + if grep -qm1 "CONFIG_RD_$$c=y" $(@D)/.config; then \ + $(call KCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config); \ + $(call KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_$$c,$(@D)/.config); \ + break; \ + fi; \ + done)
I think this is a bit too complex for something that won't really be used by
most people. Why not just remove the COMPRESSION lines from linux.mk? Then we fall back on the default if the user hasn't configured it explicitly. Gives the user the possibility to choose something else than the default, without adding complexity to buildroot.
Regards,
Arnout
Signature · 6 lines
Arnout Vandecappelle arnout at mind be Senior Embedded Software Architect +32-16-286540 Essensium/Mind http://www.mind.be G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle GPG fingerprint: 7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F
PATCH 1/1 linux: Fix initramfs compression
Quoted 15 lines · Arnout Vandecappelle
linux/linux.mk define LINUX_CONFIGURE_CMDS · line 179
Quoted 13 lines · Valentine Barshak
- $(call
KCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config)
- $(call
KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_GZIP,$(@D)/.config))linux/linux.mk +3
-0+ for c in GZIP BZIP2 LZMA XZ LZO; do \ + if grep -qm1 "CONFIG_RD_$$c=y" $(@D)/.config; then \ + $(callKCONFIG_DISABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_NONE,$(@D)/.config); \
+ $(call
KCONFIG_ENABLE_OPT,CONFIG_INITRAMFS_COMPRESSION_$$c,$(@D)/.config); \linux/linux.mk +3
-0+ break; \ + fi; \ + done)
Quoted 9 lines
I think this is a bit too complex for something that won't really be
used by
most people. Why not just remove the COMPRESSION lines from linux.mk? Then
we fall back on the default if the user hasn't configured it explicitly. Gives
the user the possibility to choose something else than the default, without adding
complexity to buildroot.
The problem here is that we can't set initramfs compression mode unless the initramfs source (CONFIG_INITRAMFS_SOURCE) is set. We can only set RAM disk compression modes that should be supported by the kernel (CONFIR_RD_...).
The source is set by buildroot. So the user has no capability to configure compression explicitly, unless he (she) sets a fake initramfs source file, which will be overridden by buildroot. IMHO, this is a bit hackish way to set anything other than default, which is COMPRESSION_NONE.
Yes, that is what most people want. I just didn't want to drop other options in case somebody wants a compressed initramfs image. This could be needed for systems with low memory, for example.
Quoted 3 lines
Regards,
Arnout
Thanks,
Val.
PATCH 1/1 linux: Fix initramfs compression
Quoted 10 lines · Valentine Barshak
The problem here is that we can't set initramfs compression mode unless the initramfs source (
CONFIG_INITRAMFS_SOURCE) is set. We can only set RAM disk compression modes that should be supported by the kernel (CONFIR_RD_...).The source is set by buildroot. So the user has no capability to configure compression explicitly, unless he (she) sets a fake initramfs source file, which will be overridden by buildroot. IMHO, this is a bit hackish way to set anything other than default, which is
COMPRESSION_NONE.Yes, that is what most people want. I just didn't want to drop other options in case somebody wants a compressed initramfs image.
This could be needed for systems with low memory, for example.
True. Still, I don't think that this corner case warrants the additional
complexity of grepping etc. in the buildroot makefile. Especially because it still doesn't give the user complete configuration freedom: if both GZIP and BZIP2 initrd compression options are enabled (like is the case in some of the kernel's defconfigs), then still GZIP will be chosen.
If we really want to support this in buildroot, then the choice should be added
to fs/initramfs/Config.in. But also here I doubt that the (maintenance) work of having this option is worth it, because it's likely that it will _never_ be used.
As you say yourself, if you really do need the option, there is a possibility
to do it. And it's not as bad as you say, because when you run 'make linux-menuconfig', buildroot will first run a 'linux-configure' so the INITRAMFS_SOURCE will already be set. (At least, I think so :-)
Regards,
Arnout
Signature · 6 lines
Arnout Vandecappelle arnout at mind be Senior Embedded Software Architect +32-16-286540 Essensium/Mind http://www.mind.be G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle GPG fingerprint: 7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F
PATCH 1/1 linux: Fix initramfs compression
Quoted 17 lines · Arnout Vandecappelle
Quoted 11 lines · Valentine Barshak
The problem here is that we can't set initramfs compression mode unless the initramfs source (
CONFIG_INITRAMFS_SOURCE) is set. We can only set RAM disk compression modes that should be supported by the kernel (CONFIR_RD_...).The source is set by buildroot. So the user has no capability to configure compression explicitly, unless he (she) sets
a fake initramfs source file, which will be overridden by buildroot. IMHO, this is a bit hackish way to set anything
other than default, which isCOMPRESSION_NONE.Quoted 4 lines
Yes, that is what most people want. I just didn't want to drop other options in case somebody wants a compressed
initramfs image.
This could be needed for systems with low memory, for example.
Quoted 8 lines
True. Still, I don't think that this corner case warrants the additional
complexity of grepping etc. in the buildroot makefile. Especially because it
still doesn't give the user complete configuration freedom: if both GZIP and
BZIP2 initrd compression options are enabled (like is the case in some of the
kernel's defconfigs), then still GZIP will be chosen.
Right.
Quoted 8 lines
If we really want to support this in buildroot, then the choice should
be added
tofs/initramfs/Config.in. But also here I doubt that the (maintenance) work of
having this option is worth it, because it's likely that it will _never_ be used.
Quoted 6 lines
As you say yourself, if you really do need the option, there is a
possibility
to do it. And it's not as bad as you say, because when you run 'make linux-menuconfig', buildroot will first run a 'linux-configure' so theINITRAMFS_SOURCEwill already be set. (At least, I think so :-)
Indeed, so it's probably better to let the kernel config handle it, instead of attempting to force any compression mode in BR.
Quoted 5 lines
Regards,
Arnout
Thanks,
Val.