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linux/usr/Kconfig
Francisco Blas Izquierdo Riera (klondike) db2aa7fd15 initramfs: allow again choice of the embedded initram compression algorithm 
Choosing the appropriate compression option when using an embedded
initramfs can result in significant size differences in the resulting
data.

This is caused by avoiding double compression of the initramfs contents.
For example on my tests, choosing CONFIG_INITRAMFS_COMPRESSION_NONE when
compressing the kernel using XZ) results in up to 500KiB differences
(9MiB to 8.5MiB) in the kernel size as the dictionary will not get
polluted with uncomprensible data and may reuse kernel data too.

Despite embedding an uncompressed initramfs, a user may want to allow
for a compressed extra initramfs to be passed using the rd system, for
example to boot a recovery system.  9ba4bcb645 ("initramfs: read
CONFIG_RD_ variables for initramfs compression") broke that behavior by
making the choice based on CONFIG_RD_* instead of adding
CONFIG_INITRAMFS_COMPRESSION_LZ4.  Saddly, CONFIG_RD_* is also used to
choose the supported RD compression algorithms by the kernel and a user
may want to support more than one.

This patch also reverts commit 3e4e0f0a87 ("initramfs: remove
"compression mode" choice") restoring back the "compression mode" choice
and includes the CONFIG_INITRAMFS_COMPRESSION_LZ4 option which was never
added.

As a result the following options are added or readed affecting the embedded
initramfs compression:
  INITRAMFS_COMPRESSION_NONE Do no compression
  INITRAMFS_COMPRESSION_GZIP Compress using gzip
  INITRAMFS_COMPRESSION_BZIP2 Compress using bzip2
  INITRAMFS_COMPRESSION_LZMA Compress using lzma
  INITRAMFS_COMPRESSION_XZ Compress using xz
  INITRAMFS_COMPRESSION_LZO Compress using lzo
  INITRAMFS_COMPRESSION_LZ4 Compress using lz4

These depend on the corresponding CONFIG_RD_* option being set (except
NONE which has no dependencies).

This patch depends on the previous one (the previous version didn't) to
simplify the way in which the algorithm is chosen and keep backwards
compatibility with the behaviour introduced by 9ba4bcb645
("initramfs: read CONFIG_RD_ variables for initramfs compression").

Link: http://lkml.kernel.org/r/57EAD77B.7090607@klondike.es
Signed-off-by: Francisco Blas Izquierdo Riera (klondike) <klondike@klondike.es>
Cc: P J P <ppandit@redhat.com>
Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-14 16:04:08 -08:00

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#
# Configuration for initramfs
#
config INITRAMFS_SOURCE
string "Initramfs source file(s)"
default ""
help
This can be either a single cpio archive with a .cpio suffix or a
space-separated list of directories and files for building the
initramfs image. A cpio archive should contain a filesystem archive
to be used as an initramfs image. Directories should contain a
filesystem layout to be included in the initramfs image. Files
should contain entries according to the format described by the
"usr/gen_init_cpio" program in the kernel tree.
When multiple directories and files are specified then the
initramfs image will be the aggregate of all of them.
See <file:Documentation/early-userspace/README> for more details.
If you are not sure, leave it blank.
config INITRAMFS_ROOT_UID
int "User ID to map to 0 (user root)"
depends on INITRAMFS_SOURCE!=""
default "0"
help
This setting is only meaningful if the INITRAMFS_SOURCE is
contains a directory. Setting this user ID (UID) to something
other than "0" will cause all files owned by that UID to be
owned by user root in the initial ramdisk image.
If you are not sure, leave it set to "0".
config INITRAMFS_ROOT_GID
int "Group ID to map to 0 (group root)"
depends on INITRAMFS_SOURCE!=""
default "0"
help
This setting is only meaningful if the INITRAMFS_SOURCE is
contains a directory. Setting this group ID (GID) to something
other than "0" will cause all files owned by that GID to be
owned by group root in the initial ramdisk image.
If you are not sure, leave it set to "0".
config RD_GZIP
bool "Support initial ramdisks compressed using gzip"
depends on BLK_DEV_INITRD
default y
select DECOMPRESS_GZIP
help
Support loading of a gzip encoded initial ramdisk or cpio buffer.
If unsure, say Y.
config RD_BZIP2
bool "Support initial ramdisks compressed using bzip2"
default y
depends on BLK_DEV_INITRD
select DECOMPRESS_BZIP2
help
Support loading of a bzip2 encoded initial ramdisk or cpio buffer
If unsure, say N.
config RD_LZMA
bool "Support initial ramdisks compressed using LZMA"
default y
depends on BLK_DEV_INITRD
select DECOMPRESS_LZMA
help
Support loading of a LZMA encoded initial ramdisk or cpio buffer
If unsure, say N.
config RD_XZ
bool "Support initial ramdisks compressed using XZ"
depends on BLK_DEV_INITRD
default y
select DECOMPRESS_XZ
help
Support loading of a XZ encoded initial ramdisk or cpio buffer.
If unsure, say N.
config RD_LZO
bool "Support initial ramdisks compressed using LZO"
default y
depends on BLK_DEV_INITRD
select DECOMPRESS_LZO
help
Support loading of a LZO encoded initial ramdisk or cpio buffer
If unsure, say N.
config RD_LZ4
bool "Support initial ramdisks compressed using LZ4"
default y
depends on BLK_DEV_INITRD
select DECOMPRESS_LZ4
help
Support loading of a LZ4 encoded initial ramdisk or cpio buffer
If unsure, say N.
choice
prompt "Built-in initramfs compression mode"
depends on INITRAMFS_SOURCE!=""
optional
help
This option allows you to decide by which algorithm the builtin
initramfs will be compressed. Several compression algorithms are
available, which differ in efficiency, compression and
decompression speed. Compression speed is only relevant
when building a kernel. Decompression speed is relevant at
each boot. Also the memory usage during decompression may become
relevant on memory constrained systems. This is usually based on the
dictionary size of the algorithm with algorithms like XZ and LZMA
featuring large dictionary sizes.
High compression options are mostly useful for users who are
low on RAM, since it reduces the memory consumption during
boot.
Keep in mind that your build system needs to provide the appropriate
compression tool to compress the generated initram cpio file for
embedding.
If in doubt, select 'None'
config INITRAMFS_COMPRESSION_NONE
bool "None"
help
Do not compress the built-in initramfs at all. This may sound wasteful
in space, but, you should be aware that the built-in initramfs will be
compressed at a later stage anyways along with the rest of the kernel,
on those architectures that support this. However, not compressing the
initramfs may lead to slightly higher memory consumption during a
short time at boot, while both the cpio image and the unpacked
filesystem image will be present in memory simultaneously
config INITRAMFS_COMPRESSION_GZIP
bool "Gzip"
depends on RD_GZIP
help
Use the old and well tested gzip compression algorithm. Gzip provides
a good balance between compression ratio and decompression speed and
has a reasonable compression speed. It is also more likely to be
supported by your build system as the gzip tool is present by default
on most distros.
config INITRAMFS_COMPRESSION_BZIP2
bool "Bzip2"
depends on RD_BZIP2
help
It's compression ratio and speed is intermediate. Decompression speed
is slowest among the choices. The initramfs size is about 10% smaller
with bzip2, in comparison to gzip. Bzip2 uses a large amount of
memory. For modern kernels you will need at least 8MB RAM or more for
booting.
If you choose this, keep in mind that you need to have the bzip2 tool
available to be able to compress the initram.
config INITRAMFS_COMPRESSION_LZMA
bool "LZMA"
depends on RD_LZMA
help
This algorithm's compression ratio is best but has a large dictionary
size which might cause issues in memory constrained systems.
Decompression speed is between the other choices. Compression is
slowest. The initramfs size is about 33% smaller with LZMA in
comparison to gzip.
If you choose this, keep in mind that you may need to install the xz
or lzma tools to be able to compress the initram.
config INITRAMFS_COMPRESSION_XZ
bool "XZ"
depends on RD_XZ
help
XZ uses the LZMA2 algorithm and has a large dictionary which may cause
problems on memory constrained systems. The initramfs size is about
30% smaller with XZ in comparison to gzip. Decompression speed is
better than that of bzip2 but worse than gzip and LZO. Compression is
slow.
If you choose this, keep in mind that you may need to install the xz
tool to be able to compress the initram.
config INITRAMFS_COMPRESSION_LZO
bool "LZO"
depends on RD_LZO
help
It's compression ratio is the second poorest amongst the choices. The
kernel size is about 10% bigger than gzip. Despite that, it's
decompression speed is the second fastest and it's compression speed
is quite fast too.
If you choose this, keep in mind that you may need to install the lzop
tool to be able to compress the initram.
config INITRAMFS_COMPRESSION_LZ4
bool "LZ4"
depends on RD_LZ4
help
It's compression ratio is the poorest amongst the choices. The kernel
size is about 15% bigger than gzip; however its decompression speed
is the fastest.
If you choose this, keep in mind that most distros don't provide lz4
by default which could cause a build failure.
endchoice
config INITRAMFS_COMPRESSION
string
default "" if INITRAMFS_COMPRESSION_NONE
default ".gz" if INITRAMFS_COMPRESSION_GZIP
default ".bz2" if INITRAMFS_COMPRESSION_BZIP2
default ".lzma" if INITRAMFS_COMPRESSION_LZMA
default ".xz" if INITRAMFS_COMPRESSION_XZ
default ".lzo" if INITRAMFS_COMPRESSION_LZO
default ".lz4" if INITRAMFS_COMPRESSION_LZ4
default ".gz" if RD_GZIP
default ".lz4" if RD_LZ4
default ".lzo" if RD_LZO
default ".xz" if RD_XZ
default ".lzma" if RD_LZMA
default ".bz2" if RD_BZIP2
default ""
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