[PATCH v3 4/8] init: add support for zstd compressed kernel

Nick Terrell
2020-03-25T19:59:00Z

From: Nick Terrell <terrelln@fb.com>

* Adds the zstd cmd to scripts/Makefile.lib
* Adds the HAVE_KERNEL_ZSTD and KERNEL_ZSTD options

Architecture specific support is still needed for decompression.

Signed-off-by: Nick Terrell <terrelln@fb.com>
---
init/Kconfig | 15 ++++++++++++++-
scripts/Makefile.lib | 15 +++++++++++++++
2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 20a6ac33761c..9b646a25918e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -173,13 +173,16 @@ config HAVE_KERNEL_LZO
config HAVE_KERNEL_LZ4
bool

+config HAVE_KERNEL_ZSTD
+ bool
+
config HAVE_KERNEL_UNCOMPRESSED
bool

choice
prompt "Kernel compression mode"
default KERNEL_GZIP
- depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
+ depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED
help
The linux kernel is a kind of self-extracting executable.
Several compression algorithms are available, which differ
@@ -258,6 +261,16 @@ config KERNEL_LZ4
is about 8% bigger than LZO. But the decompression speed is
faster than LZO.

+config KERNEL_ZSTD
+ bool "ZSTD"
+ depends on HAVE_KERNEL_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. You
+ will need at least 192 KB RAM or more for booting. The zstd command
+ line tools is required for compression.
+
config KERNEL_UNCOMPRESSED
bool "None"
depends on HAVE_KERNEL_UNCOMPRESSED
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 752ff0a225a9..4b99893efa3d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -394,6 +394,21 @@ quiet_cmd_xzkern = XZKERN $@
quiet_cmd_xzmisc = XZMISC $@
cmd_xzmisc = cat $(real-prereqs) | xz --check=crc32 --lzma2=dict=1MiB > $@

+# ZSTD
+# ---------------------------------------------------------------------------
+# Appends the uncompressed size of the data using size_append. The .zst
+# format has the size information available at the beginning of the file too,
+# but it's in a more complex format and it's good to avoid changing the part
+# of the boot code that reads the uncompressed size.
+# Note that the bytes added by size_append will make the zstd tool think that
+# the file is corrupt. This is expected.
+
+quiet_cmd_zstd = ZSTD $@
+cmd_zstd = (cat $(filter-out FORCE,$^) | \
+ zstd -19 && \
+ $(call size_append, $(filter-out FORCE,$^))) > $@ || \
+ (rm -f $@ ; false)
+
# ASM offsets
# ---------------------------------------------------------------------------

--
2.25.1