* Ideally kernel should switch to the stable lz4 format which has better specification of end of stream. For example, previously rejected files with "bogus" length and extra padding may now be accepted, whereas they were previously getting rejected by the decompressor. * This changes compatible lz4 decompressor in the kernel, which can also be used by other kernel modules such as cryptography, squashfs, zram, f2fs, comprssed kernel image, pstore. * The alignment and padding in the above test case depends on the size of the first initrd => if a given padded initrd does not reproduce the problem, try varying the size of the first initrd or that of the padding between 0.4. * With fixed kernel, /test-file in the initrd shell should exist, and should have the expected content "second-initrd". * With broken kernels, there should be dmesg error message that decoding failed, and one will observe that /test-file does not exist in the shell. * Boot above with "break=top" kernel command line. * Create a combined padded initrd of stock initrd, pad4, and the test-marker initrd created above. echo "second-initrd" > test-file, and then pack that with cpio hewc owned by root & lz4 -l. * Create an lz4 compressed initrd with a single test-file in it with some content. * Create empty padding with $ dd if=/dev/zero of=pad4 bs=1 count=4 * Multiple lz4 compressed initrds cannot be decompressed by kernel, when there is padding between them * Multiple lz4 compressed initrds cannot be decompressed by kernel, when loaded by grub * Decoding failure messages in dmsg with a single lz4 initrd Kernel should be fixed to correctly parse lz4 compressed initrds, or at least lower the warning, to not be user visible as an error. Switching from lz4 to gzip compression, simply papers over the warning, without any benefits, and slows down boot.
However, we currently believe that the decoding error reported in dmesg is actually harmless and has no impact on usability on the system. If I "update-initramfs" using gzip instead of lz, then boot up passes without decoding failed message. "initramfs unpacking failed: Decoding failed", message appears on boot up.
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