Boyer: Fedora 22 and Kernel 4.0 [LWN.net]

On his blog, Josh Boyer looks at the choice of the 4.0 kernel for Fedora 22. While the underpinnings of the live kernel patching feature have been merged, even when it is fully operational it is probably not something that Fedora (and perhaps other distributions) will use often (or at all). "In reality, we might not ever really leverage the live patching functionality in Fedora itself. It is understandable that people want to patch their kernel without rebooting, but the mechanism is mostly targeted at small bugfixes and security patches. You cannot, for example, live patch from version 4.0 to 4.1. Given that the Fedora kernel rebases both from stable kernel (e.g. 3.19.2 to 3.19.3) and major release kernels over the lifetime of a Fedora release, we don't have much opportunity to build the live patches."

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Boyer: Fedora 22 and Kernel 4.0

Posted Apr 16, 2015 22:26 UTC (Thu) by dennisjac (guest, #102016) [Link]

I always imagined that these sort of updates would only be used to give users a bit of a time window to install the proper update.
When a critical security update would have to be released it would be released both as a live patch and a regular kernel package and then you could install the kernel package and then the live patch so you could be safe immediately and delay the reboot of the system to the next maintenance window.
I never though that these live updates would replace the regular update cycle.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 17, 2015 9:26 UTC (Fri) by intgr (subscriber, #39733) [Link] (10 responses)

Obligatory conspiracy theory: live patching is an "enterprise feature" and Red Hat strategically forbids their "hobbyist" distro from making use of it.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 17, 2015 13:10 UTC (Fri) by johannbg (guest, #65743) [Link]

That would be counter productive for Red Hat since a) it want early adaptors of their products and supported applications and b) flush out bugs *before* it hits their enterprise customers.

Today the kernel community in Fedora is well run and it really cant be criticized or theorised ( conspiracy or otherwise ) about since you really cant run it any better then is already being done.

It has firm and first and foremost working distribution policies
It has low barrier of entry for participation
It's responsive both on mailinglist and in bug reports
It's community members are respectful
It's collaborative
It's open for early patch inclusion under certain condition
It provides the GA releases with the latest kernel and access to development kernel with and without debugging turned on

You can probably improve workflows to better utilize available resources but that's an continues ongoing process which as far as I know under constant review already ( at least once per development cycle ) in the community so yeah it cant really get any better than this.

On top of that during my what 8+ years of participation in Fedora I noticed never any signs Red Hat was specifically interfering with how that particular sub community with Fedora is run or how it maintains the kernel(s) in the distribution which is probably why it works so well and is the success it is today.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 21, 2015 2:29 UTC (Tue) by alison (subscriber, #63752) [Link] (8 responses)

On the contrary, it was my experience as a Fedora user for years that RedHat shipped features to desktop users that were really only of interest for the enterprise. LVM2 comes to mind. Having LVM2 as part of a default installation was just a terrible choice for someone with a single-disk laptop. The new split of Fedora into 3 parts will hopefully lessen the problem.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 21, 2015 12:54 UTC (Tue) by drag (guest, #31333) [Link] (7 responses)

lvm isn't bad for single disk. With lvm and ext4 at least it allows you to expand file systems on the fly, which is handy if you are using a computer that allows the easy installation of second disks.

Of course having the dedicated 'workstation' install should make things simplier/friendlier for desktop/laptop users. I've liked it so far.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 21, 2015 14:29 UTC (Tue) by alison (subscriber, #63752) [Link]

Just before I stopped using Fedora at 15, I borked my backup disk by accident (always check which machine's console you're typing at before using 'dd'!). The backup disk, unbeknownst to me, was in an LVM2 volume with the first disk, which was still fine. The LVM2 volume was a default created by Fedora's installer of the time. No problem, I figured, boot from SystemRescueCD, chroot to the still-correct disk, fix the second one, and promise never to do that again.

I was horrified when I found that with LVM2, it was not possible to chroot to the first disk. I had to use the LVM shell commands, in which I had no interest and for which I had no other use, to solve the problem. This fix tool an entire stressful half day. That experience was one reason I quit Fedora, which afterward took LVM out of the default install.

I have been running Fedora 21 in a QEMU and it does seem stable and functional now. Kudos to their release team for solving most of the usablility problems.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 22, 2015 9:10 UTC (Wed) by etienne (guest, #25256) [Link] (3 responses)

> lvm isn't bad for single disk.

I will not re-install a whole system to know, I never enable LVM.
Can you now do a big file with a hole on ext*fs using LVM now?
I mean: dd if=/dev/zero of=~/diskimage bs=4096 count=$((1024*1024*1024))
Does the previous command take 1 second or 10 minutes, due to LVM?

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 22, 2015 11:05 UTC (Wed) by mstone_ (subscriber, #66309) [Link] (2 responses)

LVM has nothing to do with that, and it should always take a long time to write out 4TB. I'm not entirely sure what your intent is, but I suspect you wanted "seek=$((1024*1024*1024)) count=0" instead of "count=$((1024*1024*1024))". LVM has never prevented filesystems which implement sparse files from making use of that functionality.

I'd argue that LVM is stupid for a desktop OS only because there should only be one partition anyway. But if you are going to partition, LVM is better regardless of whether the OS is "desktop" or "enterprise".

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 22, 2015 13:09 UTC (Wed) by james (guest, #1325) [Link] (1 responses)

I would argue there should be three partitions for a home system (on spinning rust, at least): two root partitions and a home partition.

When the time comes to re-install, you can re-install to the root partition that isn't currently in use, ensure that the new system is running well and has everything you need, and only then configure the system to boot to that by default and mount the home partition.

That way, you aren't committed to getting the work done in one session before your computer is usable again, and if necessary, you can discard the new install completely and very easily.

(This assumes that re-installs will be necessary from time to time, which is a separate issue...)

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 22, 2015 13:24 UTC (Wed) by mstone_ (subscriber, #66309) [Link]

I've been upgrading continuously using debian since the late 90s without a reinstall, so I don't consider needing to start from scratch to be a feature. I thought fedora had gotten better about that. At any rate, we're talking about the default for new users--I suspect that such a target audience isn't going to be switching between boot partitions and would be better served by a single partition system. If you want to do something more exotic, have at it. (Though at that point I'd return to recommending lvm, because you have a near-zero chance of correctly guessing how much space you'll want in which partition 4 years from now when you want to switch between os versions.)

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 22, 2015 10:27 UTC (Wed) by nye (guest, #51576) [Link] (1 responses)

>lvm isn't bad for single disk. With lvm and ext4 at least it allows you to expand file systems on the fly, which is handy if you are using a computer that allows the easy installation of second disks.

Don't forget that it also allows for atomic point-in-time backups via snapshots, rather than just rsync (or whatever) on the live system and hope for the best. This is definitely the standout feature for me.

Boyer: Fedora 22 and Kernel 4.0

Posted Apr 23, 2015 21:32 UTC (Thu) by sjj (guest, #2020) [Link]

It's also a convenient storage backend for virtual machines etc (saves going through another filesystem layer). This is a big part of "workstation" use for me.

I actually like the combination LVM+XFS better than BtrFS trying to smush these functionalities together. I certainly trust the combo more.