On Fri, Sep 06, 2019 at 09:16:04PM +0200, Richard Weinberger wrote:
> On Fri, Sep 6, 2019 at 1:15 PM Stefan Hajnoczi <stefanha@xxxxxxxxxx> wrote:
> >
> > Make it possible to boot directly from a virtiofs file system with tag
> > 'myfs' using the following kernel parameters:
> >
> > rootfstype=virtiofs root=myfs rw
> >
> > Booting directly from virtiofs makes it possible to use a directory on
> > the host as the root file system. This is convenient for testing and
> > situations where manipulating disk image files is cumbersome.
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> > ---
> > This patch is based on linux-next (next-20190904) but should apply
> > cleanly to other virtiofs trees.
> >
> > init/do_mounts.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/init/do_mounts.c b/init/do_mounts.c
> > index 9634ecf3743d..030be2f1999a 100644
> > --- a/init/do_mounts.c
> > +++ b/init/do_mounts.c
> > @@ -554,6 +554,16 @@ void __init mount_root(void)
> > change_floppy("root floppy");
> > }
> > #endif
> > +#ifdef CONFIG_VIRTIO_FS
> > + if (root_fs_names && !strcmp(root_fs_names, "virtiofs")) {
> > + if (!do_mount_root(root_device_name, "virtiofs",
> > + root_mountflags, root_mount_data))
> > + return;
> > +
> > + panic("VFS: Unable to mount root fs \"%s\" from virtiofs",
> > + root_device_name);
> > + }
> > +#endif
>
> I think you don't need this, you can abuse a hack for mtd/ubi in
> prepare_namespace().
> At least for 9p it works well:
> qemu-system-x86_64 -m 4G -M pc,accel=kvm -nographic -kernel
> arch/x86/boot/bzImage -append "rootfstype=9p
> rootflags=trans=virtio,version=9p2000.L root=mtdfake console=ttyS0 ro
> init=/bin/sh" -virtfs
> local,id=rootfs,path=/,security_model=passthrough,mount_tag=mtdfake
That is worse because:
1. The file system must be named "mtd*" or "ubi*".
2. When mounting fails you get confusing error messages about block
devices and partitions. These do not apply to virtio-fs or
virtio-9p.
> If this works too for virtiofs I suggest to cleanup the hack and
> generalize it. B-)
Why mtd and ubi block devices even have a special case? Maybe this code
was added because ROOT_DEV = name_to_dev_t(root_device_name) doesn't
work for "mtd:partition" device names so the regular CONFIG_BLOCK code
path doesn't work for these devices.
Given the ordering/fallback logic in prepare_namespace()/mount_root() I
don't feel comfortable changing other code paths. It's likely to break
something.
If you or others have a concrete suggestion for how to generalize this
I'm happy to try implementing it.
Stefan
Attachment:
signature.asc
Description: PGP signature
