I just tested lz4 compression with mkinitcpio after noticing it in the conf.pacnew.

When I rebooted I got the following error after grub and my computer froze:

[0.<cut>] Initramfs unpacking failed: junk in compressed archive

[0.<cut>] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

[0.<cut>] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.12.5-1-ARCH #1

[0.<cut>] Hardware name: Gigabyte Technology Co., Ltd. EP45-DS4/EP45-DS4, BIOS F10e 10/06/2010

[0.<cut>]  <3 lines, each containing 4 groups of 16 hexadecimal characters seperated by a space>

[0.<cut>] Call Trace:

[0.<cut>]  [<ffffffff814e0c60>] ? rest_init+0x90/0x90

[0.<cut>]  [<ffffffff814e0c6e>] kernel_init+0xe/0x190

[0.<cut>]  [<ffffffff814fcf3c>] ret_from_fork+0x7c/0xb0

After I disabled lz4 via a chroot the system booted successfully again.

I saw the note about using a recent version of lz4 so I installed the most recent version with pacman before running mkinitcpio -p linux and no errors were produced.

So far I haven't found anything constructive from searching the internet but three possibilities have occurred to me:

1) I first found the messages to the linux kernel mailing list adding support for lz4 to the kernel, describing it for arm and x86 so I initially assumed lz4 compressed images weren't supported with x86_64.

2) I then read the thread (https://code.google.com/p/lz4/issues/detail?id=83) linked from the lz4 commit in the mkinitcpio git repository (https://projects.archlinux.org/mkinitcpio.git/commit/?id=b5927393d103af9b8b2da80e8636b8aa52f80755), although I'm not sure I understood everything in that thread I wonder if it may be a bug in lsinitcpio.

3) grub has "insmod gzio" in grub.cfg for all arch menu entries and looking at gzio on the grub git it states it is for gzip decompression. I also found lzopio.mod in /usr/lib/grub/i386-pc and /usr/lib/grub/x86_64-efi, though I can't find any description for it I wonder if grub needs another module for decompressing the lz4 ramdisk.

I'm using kernel v3.12.5-1, grub (BIOS, not EFI) v2.00.1282.g5ae5c54-1, lz4 v109-2, mkinitcpio v16 and Arch x86_64.

Many thanks.

Please note: I copied the error message manually from the frozen computer and cut the times and the groups of hexadecimal characters relating to my motherboard/bios but I can recreate the issue to get them if it helps resolve the problem.