Inconsistent console logging using 'quiet' with encrypted root fs

Frans Pop
2009-06-28T18:05:23Z

The boot option 'quiet' sets console_loglevel to 4 (KERN_WARNING) instead
of the default 7 (KERN_DEBUG).

This is respected during the early part of the boot of my system (x86_64,
Debian stable), when kernel and initrd are loaded/run. But after the
boot process mounts root and starts udev, I suddenly get a lot of messages
of level KERN_INFO. That can't be the intention of 'quiet'...

When I look at /proc/sys/kernel/printk after the boot, I see
console_loglevel is set to 7 instead of 4.

After some instrumentation I've found the cause for this problem.

My root partition is part of an encrypted LVM volume. So the initramfs
prompts for the passphrase needed to unlock the PV, and Debian's
cryptsetup package disables console logging around that to avoid the user
interaction getting messed up by kernel printks. That this is needed can
be seen from the partial log below.

To disable and re-enable logging to console, Debian's cryptsetup uses
klogctl(6, NULL, 0) and klogctl(7, NULL, 0). Problem is that the latter
resores console_loglevel to the *default* level instead of the previous
level. And thus the 'quiet' boot becomes noisy from that point onwards.

It seems reasonable to have "enable logging to console" restore the
previous level instead. I'll follow up with a patch that does that.

Cheers,
FJP

dmesg *after* patch in follow-up mail was applied, with instrumentation:
[...]
usb 5-2: configuration #1 chosen from 1 choice
[cryptsetup prompts for passphrase -> logging disabled]
FJP: console logging disabled (console_loglevel: 1)
FJP: console_loglevel change 4->1
usb 1-2.2: new full speed USB device using ehci_hcd and address 4
ieee1394: Host added: ID:BUS[0-00:1023] GUID[001b249929192210]
usb 1-2.2: configuration #1 chosen from 1 choice
usb 1-2.3: new low speed USB device using ehci_hcd and address 5
usb 1-2.3: configuration #1 chosen from 1 choice
usbcore: registered new interface driver hiddev
input: Logitech USB Receiver as /class/input/input1
generic-usb 0003:046D:C50D.0001: input: USB HID v1.10 Mouse
[Logitech USB Receiver] on usb-0000:00:1a.7-2.3/input0
usbcore: registered new interface driver usbhid
usbhid: v2.6:USB HID core driver
usb 1-2.4: new low speed USB device using ehci_hcd and address 6
usb 1-2.4: configuration #1 chosen from 1 choice
input: USB Compliant Keyboard as /class/input/input2
generic-usb 0003:05A4:9841.0002: input: USB HID v1.10 Keyboard
[USB Compliant Keyboard] on usb-0000:00:1a.7-2.4/input0
input: USB Compliant Keyboard as /class/input/input3
generic-usb 0003:05A4:9841.0003: input: USB HID v1.10 Device
[USB Compliant Keyboard] on usb-0000:00:1a.7-2.4/input1
[incorrect passphrase entered]
FJP: console logging enabled (console_loglevel: 4)
FJP: console_loglevel change 1->4
[incorrect passphrase, so cryptsetup asks again]
FJP: console logging disabled (console_loglevel: 1)
FJP: console_loglevel change 4->1
FJP: console logging enabled (console_loglevel: 4)
FJP: console_loglevel change 1->4
PM: Starting manual resume from disk
kjournald starting. Commit interval 5 seconds
EXT3-fs: mounted filesystem with ordered data mode.
[root file system mounted] …