On 6/8/21 10:35 AM, Vivek Goyal wrote: > We want to be able to mount virtiofs as rootfs and pass appropriate > kernel command line. Right now there does not seem to be a good way > to do that. If I specify "root=myfs rootfstype=virtiofs", system > panics. > > virtio-fs: tag </dev/root> not found > .. > .. > [ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ] Whatever the best direction forward might be for kernel patches regarding 'not block device as root', it would ease learning curves if 'the patterns that set config issue X' were the same across root 'not block device options' whether cephfs, nfs, 9p, virtiofs. All of them will have to handle the selinux xattr/issue, posix and flock issues, caching etc. While by definition virtiofs has to exist only in a vm guest, the others could be baremetal or vm guest roots. (How much 9p's other-than-guest transports are used I don't know). FYI (though patching the kernel may be the best option) there is a case that does not have those kernel panics for virtiofs-root and 9p root using stock fc34. As 9p, the virtiofs method uses the initrd creation mechanisms provided by 'dracut' or 'initramfs' to provide the 'sysroot pivot glue'. On the fc34 guest a successful 'direct kernel boot' today looks like: kernel path: /vmsystems/fedora_generic/boot/vmlinuz initrd path: /vmsystems/fedora_generic/boot/initrd.img Kernel args: root=virtiofs:myfs rd.shell rd.fstab The xml to pass through virtio-fs is: <filesystem type="mount" accessmode="passthrough"> <driver type="virtiofs" queue="1024"/> <binary xattr="on"> <lock posix="on" flock="on"/> </binary> <source dir="/vmsystems/fedora_generic"/> <target dir="myfs"/> </filesystem> The guest fstab is: myfs / virtiofs defaults 0 0 HTH Harry Coin
