Re: [PATCH 2/4] fs: split rootargs into root and options

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 11/26/25 7:42 AM, Fabian Pflug wrote:
> The rootargs argument (root=/dev/etc rootwait) can be split into the
> root and options parts, which makes it easier to manipulate them both
> independently. This changes tries to be as backward compatible as
> possible and does not change the behaviour of the get functions, but
> introduces new ones to get both items seperatly.
> 
> Signed-off-by: Fabian Pflug <f.pflug@pengutronix.de>
> ---
>  common/block.c         | 42 ++++++++++++++++++-------------
>  fs/9p/vfs_super.c      |  6 ++---
>  fs/fs.c                | 57 +++++++++++++++++++++++++++++++-----------
>  fs/nfs.c               |  4 +--
>  fs/squashfs/squashfs.c | 13 ++++++----
>  fs/ubifs/ubifs.c       | 12 +++++----
>  include/block.h        |  6 +++++
>  include/fs.h           |  6 +++--
>  8 files changed, 98 insertions(+), 48 deletions(-)
> 
> diff --git a/common/block.c b/common/block.c
> index ce3aee49b4..35e90dc4a6 100644
> --- a/common/block.c
> +++ b/common/block.c
> @@ -584,34 +584,42 @@ const char *blk_type_str(enum blk_type type)
>  	}
>  }
>  
> -char *cdev_get_linux_rootarg(const struct cdev *partcdev)
> -{
> +void cdev_get_linux_root_and_opts(const struct cdev *partcdev, char** root, char** rootopts) {
> +
>  	const struct cdev *cdevm;
>  	struct block_device *blk;
> -	char *rootarg = NULL;
> -	char* root = NULL;
> +
> +	*root = NULL;
> +	*rootopts = NULL;
>  
>  	if (!partcdev)
> -		return NULL;
> +		return;
>  
>  	cdevm = partcdev->master ?: partcdev;
>  	blk = cdev_get_block_device(cdevm);
>  	if (!blk)
> -		return NULL;
> +		return;
>  
> -	if (blk->ops->get_root) {
> -		root = blk->ops->get_root(blk, partcdev);
> -		if(root) {
> -			rootarg = basprintf("root=%s", root);
> -			free(root);
> -		}
> -	}
> -	if (!rootarg && partcdev->partuuid[0] != 0)
> -		rootarg = basprintf("root=PARTUUID=%s", partcdev->partuuid);
> +	if (blk->ops->get_root)
> +		*root = blk->ops->get_root(blk, partcdev);
> +	if (!*root && partcdev->partuuid[0] != 0)
> +		*root = basprintf("PARTUUID=%s", partcdev->partuuid);
>  
>  	if (IS_ENABLED(CONFIG_ROOTWAIT_BOOTARG) && blk->rootwait)
> -		rootarg = linux_bootargs_append_rootwait(rootarg);
> +		*rootopts = xasprintf("rootwait=%d", linux_rootwait_secs);
>  
> -	return rootarg;
> +	return;
>  }
>  
> +char *cdev_get_linux_rootarg(const struct cdev *partcdev)
> +{
> +	char* root;
> +	char* rootopts;
> +
> +	cdev_get_linux_root_and_opts(partcdev, &root, &rootopts);
> +	if(!root)
> +		return NULL;
> +	if(rootopts)
> +		return xasprintf("root=%s %s", root, rootopts);
> +	return xasprintf("root=%s", root);
> +}
> diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
> index 6a451d9ef5..efc9a9193d 100644
> --- a/fs/9p/vfs_super.c
> +++ b/fs/9p/vfs_super.c
> @@ -70,11 +70,11 @@ static void v9fs_set_rootarg(struct v9fs_session_info *v9ses,
>  	trans = v9ses->clnt->trans_mod->name;
>  	path = v9ses->aname;
>  
> -	str = basprintf("root=%s rootfstype=9p rootflags=trans=%s,msize=%d,"
> +	str = basprintf("rootfstype=9p rootflags=trans=%s,msize=%d,"
>  			"cache=loose,uname=%s,dfltuid=0,dfltgid=0,aname=%s",
> -			tag, trans, v9ses->clnt->msize, tag, path);
> +			trans, v9ses->clnt->msize, tag, path);
>  
> -	fsdev_set_linux_rootarg(fsdev, str);
> +	fsdev_set_linux_root_options(fsdev, tag, str);
>  
>  	free(str);
>  }
> diff --git a/fs/fs.c b/fs/fs.c
> index 528299e039..c4f805d308 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -1226,12 +1226,26 @@ void mount_all(void)
>  	}
>  }
>  
> -void fsdev_set_linux_rootarg(struct fs_device *fsdev, const char *str)
> +void fsdev_set_linux_root_options(struct fs_device *fsdev, const char *root, const char *rootopts)
>  {
> -	fsdev->linux_rootarg = xstrdup(str);
> +	fsdev->linux_root = xstrdup(root);
> +	fsdev->linux_rootopts = xstrdup(rootopts);
>  
> -	dev_add_param_fixed(&fsdev->dev, "linux.bootargs",
> -			    "%s", fsdev->linux_rootarg);
> +	dev_add_param_fixed(&fsdev->dev, "linux.bootargs.root",
> +			    "%s", fsdev->linux_root);
> +	dev_add_param_fixed(&fsdev->dev, "linux.bootargs.rootopts",
> +			    "%s", fsdev->linux_rootopts);

Please add an entry to
Documentation/migration-guides/migration-master.rst documenting that
this variable has been replaced for file system devices by
"root={linux.bootargs.root} {linux.bootargs.rootopts}".

Thanks,
Ahmad

> +}
> +
> +void fsdev_get_linux_root_options(struct fs_device *fsdev, char **root, char **rootopts)
> +{
> +	if(fsdev) {
> +		*root = dev_get_param(&fsdev->dev, "linux.bootargs.root");
> +		*rootopts = dev_get_param(&fsdev->dev, "linux.bootargs.rootopts");
> +	} else {
> +		*root = NULL;
> +		*rootopts = NULL;
> +	}
>  }
>  
>  /**
> @@ -1245,17 +1259,27 @@ void fsdev_set_linux_rootarg(struct fs_device *fsdev, const char *str)
>  char *path_get_linux_rootarg(const char *path)
>  {
>  	struct fs_device *fsdev;
> -	const char *str;
> +	char *root;
> +	char *rootopts;
> +	char *rootarg;
>  
>  	fsdev = get_fsdevice_by_path(AT_FDCWD, path);
>  	if (!fsdev)
>  		return ERR_PTR(-EINVAL);
>  
> -	str = dev_get_param(&fsdev->dev, "linux.bootargs");
> -	if (!str)
> -		return ERR_PTR(-ENOSYS);
> +	fsdev_get_linux_root_options(fsdev, &root, &rootopts);
>  
> -	return xstrdup(str);
> +	if(!root)
> +		return ERR_PTR(-EINVAL);
> +
> +	if(rootopts) {
> +		rootarg = xasprintf("root=%s %s", root, rootopts);
> +		free(rootopts);
> +	} else {
> +		rootarg = xasprintf("root=%s", root);
> +	}
> +	free(root);
> +	return rootarg;
>  }
>  
>  /**
> @@ -3249,12 +3273,17 @@ int mount(const char *device, const char *fsname, const char *pathname,
>  
>  	fsdev->vfsmount.mnt_root = fsdev->sb.s_root;
>  
> -	if (!fsdev->linux_rootarg) {
> -		char *str;
> +	if (!fsdev->linux_root) {
> +		char *root;
> +		char *rootopts;
>  
> -		str = cdev_get_linux_rootarg(fsdev->cdev);
> -		if (str)
> -			fsdev_set_linux_rootarg(fsdev, str);
> +		cdev_get_linux_root_and_opts(fsdev->cdev, &root, &rootopts);
> +		if (root) {
> +			fsdev_set_linux_root_options(fsdev, root, rootopts);
> +			free(root);
> +			if(rootopts)
> +				free(rootopts);
> +		}
>  	}
>  
>  	path_put(&path);
> diff --git a/fs/nfs.c b/fs/nfs.c
> index 5c2476cd88..0b40c56ff3 100644
> --- a/fs/nfs.c
> +++ b/fs/nfs.c
> @@ -1558,7 +1558,7 @@ static void nfs_set_rootarg(struct nfs_priv *npriv, struct fs_device *fsdev)
>  	char *str, *tmp;
>  	const char *bootargs;
>  
> -	str = basprintf("root=/dev/nfs nfsroot=%pI4:%s%s%s", &npriv->server, npriv->path,
> +	str = basprintf("nfsroot=%pI4:%s%s%s", &npriv->server, npriv->path,
>  			  rootnfsopts[0] ? "," : "", rootnfsopts);
>  
>  	/* forward specific mount options on demand */
> @@ -1584,7 +1584,7 @@ static void nfs_set_rootarg(struct nfs_priv *npriv, struct fs_device *fsdev)
>  	if (IS_ENABLED(CONFIG_ROOTWAIT_BOOTARG))
>  		str = linux_bootargs_append_rootwait(str);
>  
> -	fsdev_set_linux_rootarg(fsdev, str);
> +	fsdev_set_linux_root_options(fsdev, "/dev/nfs", str);
>  
>  	free(str);
>  }
> diff --git a/fs/squashfs/squashfs.c b/fs/squashfs/squashfs.c
> index e30372627a..365aa1f219 100644
> --- a/fs/squashfs/squashfs.c
> +++ b/fs/squashfs/squashfs.c
> @@ -46,7 +46,8 @@ static void squashfs_set_rootarg(struct fs_device *fsdev)
>  	struct ubi_volume_info vi = {};
>  	struct ubi_device_info di = {};
>  	struct mtd_info *mtd;
> -	char *str;
> +	char *root;
> +	char *rootopts;
>  
>  	if (!IS_ENABLED(CONFIG_MTD_UBI))
>  		return;
> @@ -60,12 +61,14 @@ static void squashfs_set_rootarg(struct fs_device *fsdev)
>  	ubi_get_device_info(vi.ubi_num, &di);
>  	mtd = di.mtd;
>  
> -	str = basprintf("root=/dev/ubiblock%d_%d ubi.mtd=%s ubi.block=%d,%d rootfstype=squashfs",
> -			vi.ubi_num, vi.vol_id, mtd->cdev.partname, vi.ubi_num, vi.vol_id);
> +	root = basprintf("/dev/ubiblock%d_%d", vi.ubi_num, vi.vol_id);
> +	rootopts = basprintf("ubi.mtd=%s ubi.block=%d,%d rootfstype=squashfs",
> +			mtd->cdev.partname, vi.ubi_num, vi.vol_id);
>  
> -	fsdev_set_linux_rootarg(fsdev, str);
> +	fsdev_set_linux_root_options(fsdev, root, rootopts);
>  
> -	free(str);
> +	free(root);
> +	free(rootopts);
>  }
>  
>  static struct inode *squashfs_alloc_inode(struct super_block *sb)
> diff --git a/fs/ubifs/ubifs.c b/fs/ubifs/ubifs.c
> index 37986acbb2..9cc35fa273 100644
> --- a/fs/ubifs/ubifs.c
> +++ b/fs/ubifs/ubifs.c
> @@ -435,19 +435,21 @@ static void ubifs_set_rootarg(struct ubifs_priv *priv,
>  	struct ubi_volume_info vi = {};
>  	struct ubi_device_info di = {};
>  	struct mtd_info *mtd;
> -	char *str;
> +	char *root;
> +	char *rootopts;
>  
>  	ubi_get_volume_info(priv->ubi, &vi);
>  	ubi_get_device_info(vi.ubi_num, &di);
>  
>  	mtd = di.mtd;
>  
> -	str = basprintf("root=ubi0:%s ubi.mtd=%s rootfstype=ubifs",
> -			  vi.name, mtd->cdev.partname);
> +	root = basprintf("ubi0:%s", vi.name);
> +	rootopts = basprintf("ubi.mtd=%s rootfstype=ubifs", mtd->cdev.partname);
>  
> -	fsdev_set_linux_rootarg(fsdev, str);
> +	fsdev_set_linux_root_options(fsdev, root, rootopts);
>  
> -	free(str);
> +	free(root);
> +	free(rootopts);
>  }
>  
>  static int ubifs_probe(struct device *dev)
> diff --git a/include/block.h b/include/block.h
> index b277f590e4..ddab8bfe60 100644
> --- a/include/block.h
> +++ b/include/block.h
> @@ -85,6 +85,7 @@ static inline int block_flush(struct block_device *blk)
>  #ifdef CONFIG_BLOCK
>  unsigned file_list_add_blockdevs(struct file_list *files);
>  char *cdev_get_linux_rootarg(const struct cdev *partcdev);
> +void cdev_get_linux_root_and_opts(const struct cdev *partcdev, char** root, char** rootopts);
>  #else
>  static inline unsigned file_list_add_blockdevs(struct file_list *files)
>  {
> @@ -94,6 +95,11 @@ static inline char *cdev_get_linux_rootarg(const struct cdev *partcdev)
>  {
>  	return NULL;
>  }
> +static inline void cdev_get_linux_root_and_opts(const struct cdev *partcdev, char** root, char** rootopts)
> +{
> +	root = NULL;
> +	rootopts = NULL;
> +}
>  #endif
>  
>  static inline bool cdev_is_block_device(const struct cdev *cdev)
> diff --git a/include/fs.h b/include/fs.h
> index 98c482bbf2..c50437d609 100644
> --- a/include/fs.h
> +++ b/include/fs.h
> @@ -90,7 +90,8 @@ struct fs_device {
>  	char *path;
>  	struct list_head list;
>  	char *options;
> -	char *linux_rootarg;
> +	char *linux_root;
> +	char *linux_rootopts;
>  
>  	struct super_block sb;
>  
> @@ -159,7 +160,8 @@ const char *cdev_mount_default(struct cdev *cdev, const char *fsoptions);
>  const char *cdev_mount(struct cdev *cdev);
>  void mount_all(void);
>  
> -void fsdev_set_linux_rootarg(struct fs_device *fsdev, const char *str);
> +void fsdev_set_linux_root_options(struct fs_device *fsdev, const char *root, const char* rootopts);
> +void fsdev_get_linux_root_options(struct fs_device *fsdev, char **root, char **rootopts);
>  char *path_get_linux_rootarg(const char *path);
>  
>  static inline const char *devpath_to_name(const char *devpath)

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