usr: Add support for zstd compressed initramfs

- Add support for a zstd compressed initramfs.

- Add compression for compressing built-in initramfs with zstd.

I have tested this patch by boot testing with buildroot and QEMU.
Specifically, I booted the kernel with both a zstd and gzip compressed
initramfs, both built into the kernel and separate. I ensured that the
correct compression algorithm was used. I tested on arm, aarch64, i386,
and x86_64.

This patch has been tested in production on aarch64 and x86_64 devices.

Additionally, I have performance measurements from internal use in
production. On an aarch64 device we saw 19 second boot time improvement
from switching from lzma to zstd (27 seconds to 8 seconds). On an x86_64
device we saw a 9 second boot time reduction from switching from xz to
zstd.

Signed-off-by: Nick Terrell <terrelln@fb.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200730190841.2071656-5-nickrterrell@gmail.com

diff --git a/usr/Kconfig b/usr/Kconfig
index 96afb03..2599bc2 100644 (file)
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -100,6 +100,15 @@ config RD_LZ4
          Support loading of a LZ4 encoded initial ramdisk or cpio buffer
          If unsure, say N.
 
+config RD_ZSTD
+       bool "Support initial ramdisk/ramfs compressed using ZSTD"
+       default y
+       depends on BLK_DEV_INITRD
+       select DECOMPRESS_ZSTD
+       help
+         Support loading of a ZSTD encoded initial ramdisk or cpio buffer.
+         If unsure, say N.
+
 choice
        prompt "Built-in initramfs compression mode"
        depends on INITRAMFS_SOURCE != ""
@@ -196,6 +205,17 @@ config INITRAMFS_COMPRESSION_LZ4
          If you choose this, keep in mind that most distros don't provide lz4
          by default which could cause a build failure.
 
+config INITRAMFS_COMPRESSION_ZSTD
+       bool "ZSTD"
+       depends on RD_ZSTD
+       help
+         ZSTD is a compression algorithm targeting intermediate compression
+         with fast decompression speed. It will compress better than GZIP and
+         decompress around the same speed as LZO, but slower than LZ4.
+
+         If you choose this, keep in mind that you may need to install the zstd
+         tool to be able to compress the initram.
+
 config INITRAMFS_COMPRESSION_NONE
        bool "None"
        help

diff --git a/usr/Makefile b/usr/Makefile
index c12e6b1..b1a81a4 100644 (file)
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -15,6 +15,7 @@ compress-$(CONFIG_INITRAMFS_COMPRESSION_LZMA) := lzma
 compress-$(CONFIG_INITRAMFS_COMPRESSION_XZ)    := xzmisc
 compress-$(CONFIG_INITRAMFS_COMPRESSION_LZO)   := lzo
 compress-$(CONFIG_INITRAMFS_COMPRESSION_LZ4)   := lz4
+compress-$(CONFIG_INITRAMFS_COMPRESSION_ZSTD)  := zstd
 
 obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o