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On Tue, Jan 29, 2019 at 1:39 PM Alan Mackenzie <acm@×××.de> wrote: |
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> |
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> On Tue, Jan 29, 2019 at 12:58:38 -0500, Rich Freeman wrote: |
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> > Can't say I've tried it recently, but I'd be shocked if it changed |
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> > much. The linux kernel guys generally consider this somewhat |
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> > deprecated behavior, and prefer that users use an initramfs for this |
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> > sort of thing. It is exactly the sort of problem an initramfs was |
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> > created to fix. |
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> |
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> An initramfs is conceptually so ugly that I view it as a workaround, not |
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> a fix, to whatever problem it's applied to. |
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Not sure why you would think this. It is just a cpio archive of a |
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root filesystem that the kernel runs as a generic bootstrap. |
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This means that your bootstrap for initializing your root and |
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everything else can use any userspace tool that exists for linux. |
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A similar concept lies at the heart of coreboot - using a generic |
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kernel/userpace as a firmware bootloader making it far more flexible. |
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An initramfs is basically just a fairly compact linux distro. It |
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works the same as any distro. The kernel runs init, and init does its |
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thing. By convention that init will mount the real root and then exec |
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the init inside, but it doesn't have to work that way. Heck, you can |
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run a system with nothing but an initramfs and no other root |
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filesystem. |
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> It would surely be a bug if the kernel were capable of manipulating RAIDs, but not of initialising |
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> and mounting them. |
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Linus would disagree with you there, and has said as much publicly. |
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He does not consider initialization to be the responsibility of kernel |
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space long-term, and prefers that this happen in user-space. |
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Some of the lvm and mdadm support remains for legacy reasons, but you |
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probably won't see initialization of newer volume/etc managers |
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supported directly in the kernel. |
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> > Honestly, I'd just bite the bullet and use dracut if you want your OS |
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> > on RAID/etc. It is basically a one-liner at this point to install and |
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> > a relatively small tweak to your GRUB config (automatic if using |
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> > mkconfig). Dracut will respect your mdadm.conf, and just about all |
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> > your other config info in /etc. The only gotcha is rebuilding your |
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> > initramfs if it drastically changes (but, drastically changing your |
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> > root filesystem is something that requires care anyway). |
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> |
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> Well, at the moment my system's not broken, hence doesn't need fixing. |
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> Last time I looked at Dracut, it would only work in a kernel built with |
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> modules enabled, ruling out my setup. |
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That is news to me. Obviously it needs whatever drivers it needs, but |
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I don't see why it would care if they are built in-kernel vs |
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in-module. |
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> Also, without putting in a LOT of time and study, dracut is a massive, |
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> opaque mystery. I've got a pretty good mental picture of how my system |
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> works, and introducing an initramfs would degrade that picture |
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> enormously. That means if any problems happened with the initramfs, I'd |
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> be faced with many days study to get to grips with it. |
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Sure, if you want to know exactly how it works that is true, but the |
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same is true of openrc or any other piece of software on your system. |
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Dracut is highly modular and phase/hook-driven so it isn't too hard to |
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grok. Most of it is just bash/dash scripts. |
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-- |
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Rich |
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