[RESEND v2 PATCH] init/do_mounts.c: add virtiofs root fs support

[Stefan Hajnoczi]

On Fri, Feb 24, 2023 at 03:37:51PM +0100, David Heidelberg wrote:
> From: Stefan Hajnoczi <stefanha at redhat.com>
> 
> 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.
> 
> Reviewed-by: Helen Koike <helen.koike at collabora.com>
> Signed-off-by: Stefan Hajnoczi <stefanha at redhat.com>
> Signed-off-by: David Heidelberg <david at ixit.cz>
> ---
> v2: added Reviewed-by and CCed everyone interested.
> 
> We have used this option in Mesa3D CI for testing crosvm for
> more than one years and it's proven to work reliably.
> 
> We are working on effort to removing custom patches to be able to do 
> automated apply and test of patches from any tree.                              
> 
> https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/.gitlab-ci/crosvm-runner.sh#L85
>  init/do_mounts.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Vivek, do you remember where we ended up with boot from virtiofs? I
thought a different solution was merged some time ago.

There is documentation from the virtiofs community here:
https://virtio-fs.gitlab.io/howto-boot.html

Stefan

> 
> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index 811e94daf0a8..11c11abe23d7 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -578,6 +578,16 @@ void __init mount_root(void)
>  			printk(KERN_ERR "VFS: Unable to mount root fs via SMB.\n");
>  		return;
>  	}
> +#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
>  	if (ROOT_DEV == 0 && root_device_name && root_fs_names) {
>  		if (mount_nodev_root() == 0)
> -- 
> 2.39.1
> 
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