linux-kernel - Re: [PATCH v2 0/2] Add support to boot virtiofs and 9pfs as rootfs

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Date:   Thu, 17 Jun 2021 11:14:00 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtio-fs@...hat.com, miklos@...redi.hu, stefanha@...hat.com,
        dgilbert@...hat.com, viro@...iv.linux.org.uk, dhowells@...hat.com,
        richard.weinberger@...il.com, hch@...radead.org,
        asmadeus@...ewreck.org, v9fs-developer@...ts.sourceforge.net
Subject: Re: [PATCH v2 0/2] Add support to boot virtiofs and 9pfs as rootfs

Why not something like the version below that should work for all nodev
file systems?

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 74aede860de7..3c5676603fef 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -530,6 +530,39 @@ static int __init mount_cifs_root(void)
 }
 #endif
 
+static int __init mount_nodev_root(void)
+{
+	struct file_system_type *fs = get_fs_type(root_fs_names);
+	char *fs_names, *p;
+	int err = -ENODEV;
+
+	if (!fs)
+		goto out;
+	if (fs->fs_flags & FS_REQUIRES_DEV)
+		goto out_put_filesystem;
+
+	fs_names = (void *)__get_free_page(GFP_KERNEL);
+	if (!fs_names)
+		goto out_put_filesystem;
+	get_fs_names(fs_names);
+
+	for (p = fs_names; *p; p += strlen(p) + 1) {
+		err = do_mount_root(root_device_name, p, root_mountflags,
+					root_mount_data);
+		if (!err)
+			break;
+		if (err != -EACCES && err != -EINVAL)
+			panic("VFS: Unable to mount root \"%s\" (%s), err=%d\n",
+				      root_device_name, p, err);
+	}
+
+	free_page((unsigned long)fs_names);
+out_put_filesystem:
+	put_filesystem(fs);
+out:
+	return err;
+}
+
 void __init mount_root(void)
 {
 #ifdef CONFIG_ROOT_NFS
@@ -546,6 +579,8 @@ void __init mount_root(void)
 		return;
 	}
 #endif
+	if (ROOT_DEV == 0 && mount_nodev_root() == 0)
+		return;
 #ifdef CONFIG_BLOCK
 	{
 		int err = create_dev("/dev/root", ROOT_DEV);