[gentoo-user] Persistence of ZFS /dev/zvol/rpool/swap

[Pariksheet Nanda]

Hi folks,

I've followed fearedbliss' guide for installing Gentoo on ZFS [1] and am
trying to understand why /dev/zol/rpool/swap does not show up on reboot
even though I saw it initially when creating the zvol and can still see it
with zfs list:

xm2 ~ # zfs list
NAME                USED  AVAIL  REFER  MOUNTPOINT
rpool              29.1G   176G    96K  none
rpool/HOME         4.98G   176G  4.98G  /home
rpool/ROOT         7.10G   176G    96K  none
rpool/ROOT/gentoo  7.10G   176G  7.10G  /
rpool/swap         17.0G   193G   354M  -
xm2 ~ # ls /dev/zvol
ls: cannot access '/dev/zvol': No such file or directory
xm2 ~ #

I'm actually surprised my system boots at all, because /etc/fstab looks for
that partition to be the swap:

xm2 ~ # grep ^/dev /etc/fstab
/dev/zvol/rpool/swap    none        swap        sw,discard    0 0
xm2 ~ #

My best guesses at the problem are either that it's udev related or that
the various ZFS services need to be better configured to expose the zvol.
I read the "Admin Documentation" links on the zfsonlinux.org website
looking for mentions on "zvol" and the only relevant section seems to be
the `zpool import` should apply `zfs share -a` to zvols [2].  Maybe I need
to run `zfs share`?  But that doesn't seem to help:

xm2 ~ # zfs share rpool/swap
cannot open 'rpool/swap': operation not applicable to datasets of this type
xm2 ~ # zfs share -a
xm2 ~ # ls /dev/zvol
ls: cannot access '/dev/zvol': No such file or directory
xm2 ~ #

I haven't posted on this list in many years, so go easy on me :)

Pariksheet

[1]
https://wiki.gentoo.org/wiki/User:Fearedbliss/Installing_Gentoo_Linux_On_ZFS#Create_your_swap_zvol
[2] http://open-zfs.org/wiki/System_Administration#Boot_process