linux-fsdevel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: viro@zeniv.linux.org.uk
Cc: Vivek Goyal <vgoyal@redhat.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtio-fs@redhat.com
Subject: [PATCH 2/2] init: allow mounting arbitrary non-blockdevice filesystems as root
Date: Mon, 21 Jun 2021 08:26:57 +0200	[thread overview]
Message-ID: <20210621062657.3641879-3-hch@lst.de> (raw)
In-Reply-To: <20210621062657.3641879-1-hch@lst.de>

Currently the only non-blockdevice filesystems that can be used as the
initial root filesystem are NFS and CIFS, which use the magic
"root=/dev/nfs" and "root=/dev/cifs" syntax that requires the root
device file system details to come from filesystem specific kernel
command line options.

Add a little bit of new code that allows to just pass arbitrary
string mount options to any non-blockdevice filesystems so that it can
be mounted as the root file system.

For example a virtiofs root file system can be mounted using the
following syntax:

"root=myfs rootfstype=virtiofs rw"

Based on an earlier patch from Vivek Goyal <vgoyal@redhat.com>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 init/do_mounts.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index ec32de3ad52b..bdeb90b8d669 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -534,6 +534,45 @@ static int __init mount_cifs_root(void)
 }
 #endif
 
+static bool __init fs_is_nodev(char *fstype)
+{
+	struct file_system_type *fs = get_fs_type(fstype);
+	bool ret = false;
+
+	if (fs) {
+		ret = !(fs->fs_flags & FS_REQUIRES_DEV);
+		put_filesystem(fs);
+	}
+
+	return ret;
+}
+
+static int __init mount_nodev_root(void)
+{
+	char *fs_names, *fstype;
+	int err = -EINVAL;
+
+	fs_names = (void *)__get_free_page(GFP_KERNEL);
+	if (!fs_names)
+		return -EINVAL;
+	split_fs_names(fs_names, root_fs_names);
+
+	for (fstype = fs_names; *fstype; fstype += strlen(fstype) + 1) {
+		if (!fs_is_nodev(fstype))
+			continue;
+		err = do_mount_root(root_device_name, fstype, 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, fstype, err);
+	}
+
+	free_page((unsigned long)fs_names);
+	return err;
+}
+
 void __init mount_root(void)
 {
 #ifdef CONFIG_ROOT_NFS
@@ -550,6 +589,10 @@ void __init mount_root(void)
 		return;
 	}
 #endif
+	if (ROOT_DEV == 0 && root_device_name && root_fs_names) {
+		if (mount_nodev_root() == 0)
+			return;
+	}
 #ifdef CONFIG_BLOCK
 	{
 		int err = create_dev("/dev/root", ROOT_DEV);
-- 
2.30.2


  parent reply	other threads:[~2021-06-21  6:28 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-21  6:26 support booting of arbitrary non-blockdevice file systems v2 Christoph Hellwig
2021-06-21  6:26 ` [PATCH 1/2] init: split get_fs_names Christoph Hellwig
2021-06-21 14:46   ` Al Viro
2021-06-21 14:51     ` Al Viro
2021-06-21 14:53     ` Christoph Hellwig
2021-06-21 14:59       ` Al Viro
2021-06-21 15:09   ` Matthew Wilcox
2021-06-21 15:22     ` Christoph Hellwig
2021-06-21  6:26 ` Christoph Hellwig [this message]
2021-06-21 13:31 ` [Virtio-fs] support booting of arbitrary non-blockdevice file systems v2 Stefan Hajnoczi
2021-06-21 14:35 ` Vivek Goyal
2021-06-22  8:12 ` [PATCH 3/2] fs: simplify get_filesystem_list / get_all_fs_names Christoph Hellwig
2021-06-22  8:36   ` [Virtio-fs] " Stefan Hajnoczi
2021-06-29 20:50     ` Vivek Goyal
2021-06-30  5:36       ` Christoph Hellwig
2021-06-30 17:33         ` Vivek Goyal
2021-07-07 21:04         ` Vivek Goyal
2021-07-07 21:06           ` Vivek Goyal
2021-07-08 12:59             ` Vivek Goyal
2021-07-12 18:21               ` Vivek Goyal
2021-07-13  5:40                 ` Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2021-06-17 15:36 support booting of arbitrary non-blockdevice file systems Christoph Hellwig
2021-06-17 15:36 ` [PATCH 2/2] init: allow mounting arbitrary non-blockdevice filesystems as root Christoph Hellwig
2021-06-17 16:26   ` Vivek Goyal
2021-06-18 13:20     ` Christoph Hellwig
2021-06-18 14:10       ` Vivek Goyal

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210621062657.3641879-3-hch@lst.de \
    --to=hch@lst.de \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=vgoyal@redhat.com \
    --cc=viro@zeniv.linux.org.uk \
    --cc=virtio-fs@redhat.com \
    --subject='Re: [PATCH 2/2] init: allow mounting arbitrary non-blockdevice filesystems as root' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).