On Thu, Jun 17, 2021 at 12:26:10PM -0400, Vivek Goyal wrote: > Not sure what FS_BINARY_MOUNTDATA is why fs should not have that set. nfs > seems to set it too. So that means they can't use try_mount_nodev().
We can't really pass actual binary mountdata using the string separation scheme used by the rootfstype= option. But given that NFS only uses binary mountdata for legacy reasons and people get what they ask for using the option I think we can drop the check. > In case of success err == 0, but we still panic(). We will need to > check for success as well. Indeed. > root_fs_names can be NULL and it crashes with NULL pointer dereference. True. What do you think of this version? --- >From 141caa79a619b5f5d100eeb8e94ecf8b3b1c9af7 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig <[email protected]> Date: Fri, 18 Jun 2021 15:10:39 +0200 Subject: init: allow mounting arbitrary non-blockdevice filesystems as root 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 <[email protected]>. Signed-off-by: Christoph Hellwig <[email protected]> --- init/do_mounts.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/init/do_mounts.c b/init/do_mounts.c index ec32de3ad52b..66c47193e9ee 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_fs_names) { + if (mount_nodev_root() == 0) + return; + } #ifdef CONFIG_BLOCK { int err = create_dev("/dev/root", ROOT_DEV); -- 2.30.2 _______________________________________________ Virtio-fs mailing list [email protected] https://listman.redhat.com/mailman/listinfo/virtio-fs
