Kernels with builtin ZFS support lack a way to mount a ZFS dataset as a rootfs without an initramfs

[ryao]

Currently, the only way to do this is with an initramfs. It would be nice to support mounting the rootfs from a ZFS dataset without an initramfs when ZFS is built into the kernel binary.

[behlendorf]

I'm not sure I exactly understand the issue here.

[ryao]

On Solaris, GRUB provides the kernel with information on the root pool, which is used to mount the root filesystem:

https://github.com/dajhorn/pkg-zfs/wiki/Dual-booting-Linux-and-Solaris-with-ZFS-aware-GRUB-0.97

On Linux, there is no equivalent. Currently, people circumvent this by using an initramfs image. This made sense when ZFS existed solely as an external module, but it is a hack when ZFS is built into the kernel. It would be nice to have a way to boot without an initramfs when ZFS support is built into the kernel.

This is probably a low priority for all contributors, but I thought it would be worthwhile to have an issue for it so that people know that we are aware of it

[ryao]

spa_import_rootpool() in ./module/zfs/spa.c could be used to enable this to work. We just need to provide GRUB with a way to pass the requisite information to the kernel module and have the kernel module run this routine when it sees it during initialization.

[schreiberstein]

Is there anyone working on this? I would love to see this feature!

[FransUrbo]

@ryao Is this still an issue with latest grub (which have quite extensive zfs support)?

[ryao]

@FransUrbo It is an issue because the module makes upcalls to userspace.

[bunder2015]

I am also interested in this feature as well.

[kernelOfTruth]

+1

[jwezel]

It's 2017 and we absolutely need this.

[henglinli]

initramfs less boot zfs root feature should the advantage against btrfs, we need this feautre

[rlaager]

I'm closing this in favor of #4300, which has more notes.