[arch-projects] [mkinitcpio] lz4 support

[Chris Rule]

Hi, sorry in advance if I haven't reported this correctly. I was hesitant
to file a bug report until I was sure it is a bug, and what the bug was in.

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>]  [<ffffffff814ee44b>] dump_stack+0x54/0x8d
[0.<cut>]  [<ffffffff814eb62c>] panic+0xc8/0x1d7
[0.<cut>]  [<ffffffff818e2458>] mount_block_root+0x2a1/0x2b0
[0.<cut>]  [<ffffffff818e24ba>] mount_root+0x53/0x56
[0.<cut>]  [<ffffffff818e25f4>] prepare_namespace+0x137/0x16f
[0.<cut>]  [<ffffffff818e20df>] kernel_init_freeable+0x1d2/0x1e0
[0.<cut>]  [<ffffffff818e189a>] ? do_early_param+0x88/0x88
[0.<cut>]  [<ffffffff814e0c60>] ? rest_init+0x90/0x90
[0.<cut>]  [<ffffffff814e0c6e>] kernel_init+0xe/0x190
[0.<cut>]  [<ffffffff814fcf3c>] ret_from_fork+0x7c/0xb0
[0.<cut>]  [<ffffffff814e0c60>] ? rest_init+0x90/0x90

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.

Has a lz4 compressed ramdisk worked for anyone else and if it has can you
help me rule out any of these options or does anyone think I missed
something?

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.
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