Re: Can anyone boot a system using btrfs root with linux 3.14 or newer?

Chris Murphy
2014-04-25T00:04:06Z

On Apr 24, 2014, at 5:07 PM, Marc MERLIN <marc@merlins.org> wrote:
>
>
> In 3.14 the device shows up before btrfs is loaded:
> sd 2:0:0:0: [sda] Cache data unavailable
> sd 2:0:0:0: [sda] Assuming drive cache: write through
> sd 2:0:0:0: [sda] Attached SCSI disk
> (...)
> Btrfs loaded

Same for me though, and I can boot.

[ 0.693215] ata1.00: ATA-6: VBOX HARDDISK, 1.0, max UDMA/133
[ 0.693799] ata1.00: 167772160 sectors, multi 128: LBA48 NCQ (depth 31/32)
[ 0.694153] ata1.00: configured for UDMA/133
[ 0.695475] scsi 0:0:0:0: Direct-Access ATA VBOX HARDDISK 1.0 PQ: 0 ANSI: 5
[ 0.699386] sd 0:0:0:0: [sda] 167772160 512-byte logical blocks: (85.8 GB/80.0 GiB)
[ 0.699443] sd 0:0:0:0: Attached scsi generic sg0 type 0
[ 0.700604] sd 0:0:0:0: [sda] Write Protect is off
[ 0.701151] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[ 0.701187] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[ 0.707841] sda: sda1 sda2 sda3
[ 0.709846] sd 0:0:0:0: [sda] Attached SCSI disk
(…)
[ 2.380090] bio: create slab <bio-1> at 1
[ 2.384645] Btrfs loaded

So I don't think the order is it. The biggest difference I'm seeing between the 3.13.11 and 3.14.1 dmesg's provided:

3.13.11:
[ 1.861740] bio: create slab <bio-1> at 1
[ 1.863389] Btrfs loaded

3.14.1:
[ 3.949312] bio: create slab <bio-1> at 1
[ 3.950942] Btrfs loaded

It's happening much later, and it's right at this point VFS complains:
[ 4.182603] VFS: Cannot open root device "sda2" or unknown-block(8,2): error -38

The 8,2 message is consistent with the kernel not knowing what file system sda2 is. Seems like it's saying "I see sda2, I know you want to use it as root, but I don't know what's there - *poof*" and it panics.

If rootwait alone doesn't work, I wonder if root=uuid=2ba08fbc-4b95-46cc-b638-299f16462620 instead of root=/dev/sda2 will work along with rootwait. It should then wait for that fs uuid to become available, rather than waiting for sda2 to become available.

I vaguely recall there recently being btrfs boot problems with the module compiled in…

Chris Murphy