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

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Thank you all!

We'll drop this patch in next MesaCI kernel uprev without this patch!

David

On 27/02/2023 19:06, Vivek Goyal wrote:
On Mon, Feb 27, 2023 at 10:53:45AM -0500, Stefan Hajnoczi wrote:
On Fri, Feb 24, 2023 at 03:37:51PM +0100, David Heidelberg wrote:
From: Stefan Hajnoczi <stefanha@xxxxxxxxxx>

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@xxxxxxxxxxxxx>
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Signed-off-by: David Heidelberg <david@xxxxxxx>
---
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.
We merged a patch from Christoph Hellwig to support this.

commit f9259be6a9e7c22d92e5a5000913147ae17e8321
Author: Christoph Hellwig <hch@xxxxxx>
Date:   Wed Jul 14 16:23:20 2021 -0400

     init: allow mounting arbitrary non-blockdevice filesystems as root

Now one should be able to mount virtiofs using following syntax.

"root=myfs rootfstype=virtiofs rw"

IIUC, this patch should not be required anymore.

Thanks
Vivek

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


--
David Heidelberg
Consultant Software Engineer




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