On Fri, Jun 18, 2021 at 09:07:14AM +0200, Miklos Szeredi wrote: > On Mon, 14 Jun 2021 at 19:45, Vivek Goyal <vgoyal@xxxxxxxxxx> 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) ] > > > > Basic problem here is that kernel assumes that device identifier > > passed in "root=" is a block device. But there are few execptions > > to this rule to take care of the needs of mtd, ubi, NFS and CIFS. > > > > For example, mtd and ubi prefix "mtd:" or "ubi:" respectively. > > > > "root=mtd:<identifier>" or "root=ubi:<identifier>" > > > > NFS and CIFS use "root=/dev/nfs" and CIFS passes "root=/dev/cifs" and > > actual root device details come from filesystem specific kernel > > command line options. > > > > virtiofs does not seem to fit in any of the above categories. In fact > > we have 9pfs which can be used to boot from but it also does not > > have a proper syntax to specify rootfs and does not fit into any of > > the existing syntax. They both expect a device "tag" to be passed > > in a device to be mounted. And filesystem knows how to parse and > > use "tag". > > > > So there seem to be a class of filesystems which specify root device > > using a "tag" which is understood by the filesystem. And filesystem > > simply expects that "tag" to be passed as "source" of mount and > > how to mount filesystem using that "tag" is responsibility of filesystem. > > > > This patch proposes that we internally create a list of filesystems > > which pass a "tag" in "root=<tag>" and expect that tag to be passed > > as "source" of mount. With this patch I can boot into virtiofs rootfs > > with following syntax. > > > > "root=myfs rootfstype=virtiofs rw" > > The syntax and the implementation looks good. > > Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Thanks Miklos. Now Christoph has come up with another patch series to achieve the same. And that patches series looks better than my patches. https://lore.kernel.org/linux-fsdevel/20210617153649.1886693-1-hch@xxxxxx/ There are couple of minor issues to be taken care of. I am hoping after that these patches can be merged. Thanks Vivek
