Re: [PATCH 3/3] fuse: allow setting of root nodeid

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Apr 29, 2026 at 07:33:05AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Provide a new mount option so that fuse servers can actually set the
> root nodeid.
> 
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
>  fs/fuse/fuse_i.h |    2 ++
>  fs/fuse/inode.c  |   11 +++++++++++
>  2 files changed, 13 insertions(+)
> 
> 
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index a9ca0e936524e7..95b37f4660cc1d 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -642,6 +642,7 @@ static inline bool fuse_is_inode_dax_mode(enum fuse_dax_mode mode)
>  struct fuse_fs_context {
>  	struct fuse_dev *fud;
>  	unsigned int rootmode;
> +	u64 root_nodeid;
>  	kuid_t user_id;
>  	kgid_t group_id;
>  	bool is_bdev:1;
> @@ -654,6 +655,7 @@ struct fuse_fs_context {
>  	bool no_control:1;
>  	bool no_force_umount:1;
>  	bool legacy_opts_show:1;
> +	bool root_nodeid_present:1;
>  	enum fuse_dax_mode dax_mode;
>  	unsigned int max_read;
>  	unsigned int blksize;
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index d883c9e3543f5c..d48a76e6d17995 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -816,6 +816,7 @@ enum {
>  	OPT_ALLOW_OTHER,
>  	OPT_MAX_READ,
>  	OPT_BLKSIZE,
> +	OPT_ROOT_NODEID,
>  	OPT_ERR
>  };
>  
> @@ -830,6 +831,7 @@ static const struct fs_parameter_spec fuse_fs_parameters[] = {
>  	fsparam_u32	("max_read",		OPT_MAX_READ),
>  	fsparam_u32	("blksize",		OPT_BLKSIZE),
>  	fsparam_string	("subtype",		OPT_SUBTYPE),
> +	fsparam_u64	("root_nodeid",		OPT_ROOT_NODEID),
>  	{}
>  };
>  
> @@ -950,6 +952,11 @@ static int fuse_parse_param(struct fs_context *fsc, struct fs_parameter *param)
>  		ctx->blksize = result.uint_32;
>  		break;
>  
> +	case OPT_ROOT_NODEID:
> +		ctx->root_nodeid = result.uint_64;

Codex says we need to reject zero nodeids here, because fuse doesn't
consider that to be a valid id.  Generally speaking, unix filesystems
don't allow a zero inumber so ... yeah.

--D

> +		ctx->root_nodeid_present = true;
> +		break;
> +
>  	default:
>  		return -EINVAL;
>  	}
> @@ -987,6 +994,8 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
>  			seq_printf(m, ",max_read=%u", fc->max_read);
>  		if (sb->s_bdev && sb->s_blocksize != FUSE_DEFAULT_BLKSIZE)
>  			seq_printf(m, ",blksize=%lu", sb->s_blocksize);
> +		if (fc->root_nodeid && fc->root_nodeid != FUSE_ROOT_ID)
> +			seq_printf(m, ",root_nodeid=%llu", fc->root_nodeid);
>  	}
>  #ifdef CONFIG_FUSE_DAX
>  	if (fc->dax_mode == FUSE_DAX_ALWAYS)
> @@ -2052,6 +2061,8 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
>  	sb->s_flags |= SB_POSIXACL;
>  
>  	fc->default_permissions = ctx->default_permissions;
> +	if (ctx->root_nodeid_present)
> +		fc->root_nodeid = ctx->root_nodeid;
>  	fc->allow_other = ctx->allow_other;
>  	fc->user_id = ctx->user_id;
>  	fc->group_id = ctx->group_id;
> 
>