[PATCH] init/do_mounts.c: add virtiofs root fs support

[PATCH] init/do_mounts.c: add virtiofs root fs support

[Stefan Hajnoczi]

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@redhat.com>
---
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
 #ifdef CONFIG_BLOCK
 	{
 		int err = create_dev("/dev/root", ROOT_DEV);
-- 
2.21.0

Re: [PATCH] init/do_mounts.c: add virtiofs root fs support

[Richard Weinberger]

On Fri, Sep 6, 2019 at 1:15 PM Stefan Hajnoczi <stefanha@redhat.com> 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@redhat.com>
> ---
> 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

If this works too for virtiofs I suggest to cleanup the hack and
generalize it. B-)

-- 
Thanks,
//richard

Re: [PATCH] init/do_mounts.c: add virtiofs root fs support

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 2823 bytes --]

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@redhat.com> 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@redhat.com>
> > ---
> > 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 #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [Virtio-fs] [PATCH] init/do_mounts.c: add virtiofs root fs support

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 3033 bytes --]

On Mon, Sep 09, 2019 at 09:00:39AM +0200, Stefan Hajnoczi wrote:
> 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@redhat.com> 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@redhat.com>
> > > ---
> > > 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.

Ping

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH] init/do_mounts.c: add virtiofs root fs support

[Richard Weinberger]

On Mon, Sep 9, 2019 at 9:00 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 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@redhat.com> wrote:
> > 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.

This is the current situation, I'm not saying it is perfect. But
before we add another
special case for a filesystem we should at least try to consolidate this stuff.

> > 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.

ubi and mtd are not block devices, they are character devices.
That's why the hack with name matching was added a long time ago.

> 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.

mtd, ubi, virtiofs and 9p have one thing in common, they are not block devices.
What about a new miscroot= kernel parameter?

-- 
Thanks,
//richard

Re: [PATCH] init/do_mounts.c: add virtiofs root fs support

[Al Viro]

On Tue, Sep 17, 2019 at 08:19:55PM +0200, Richard Weinberger wrote:

> mtd, ubi, virtiofs and 9p have one thing in common, they are not block devices.
> What about a new miscroot= kernel parameter?

How about something like xfs!sda5 or nfs!foo.local.net/bar, etc.?  With
ubi et.al. covered by the same syntax...

Re: [Virtio-fs] [PATCH] init/do_mounts.c: add virtiofs root fs support

[Dr. David Alan Gilbert]

* Al Viro (viro@zeniv.linux.org.uk) wrote:
> On Tue, Sep 17, 2019 at 08:19:55PM +0200, Richard Weinberger wrote:
> 
> > mtd, ubi, virtiofs and 9p have one thing in common, they are not block devices.
> > What about a new miscroot= kernel parameter?
> 
> How about something like xfs!sda5 or nfs!foo.local.net/bar, etc.?  With
> ubi et.al. covered by the same syntax...

Would Stefan's patch work if there was just a way to test for non-block
based fileystsmes and we replaced
   !strcmp(root_fs_names, "virtiofs") by
   not_block_based_fs(root_fs_names)

Or is there some magic that the other filesystems do that's specific?

Dave

> _______________________________________________
> Virtio-fs mailing list
> Virtio-fs@redhat.com
> https://www.redhat.com/mailman/listinfo/virtio-fs
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Virtio-fs] [PATCH] init/do_mounts.c: add virtiofs root fs support

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 773 bytes --]

On Tue, Sep 17, 2019 at 07:34:25PM +0100, Dr. David Alan Gilbert wrote:
> * Al Viro (viro@zeniv.linux.org.uk) wrote:
> > On Tue, Sep 17, 2019 at 08:19:55PM +0200, Richard Weinberger wrote:
> > 
> > > mtd, ubi, virtiofs and 9p have one thing in common, they are not block devices.
> > > What about a new miscroot= kernel parameter?
> > 
> > How about something like xfs!sda5 or nfs!foo.local.net/bar, etc.?  With
> > ubi et.al. covered by the same syntax...
> 
> Would Stefan's patch work if there was just a way to test for non-block
> based fileystsmes and we replaced
>    !strcmp(root_fs_names, "virtiofs") by
>    not_block_based_fs(root_fs_names)
> 
> Or is there some magic that the other filesystems do that's specific?

I will try this.

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]