[PATCH v2] erofs: support idmapped mounts

[Christian Brauner]

[adding fsdevel for awareness]

On Tue, May 17, 2022 at 06:41:03PM +0800, Chao Yu wrote:
> This patch enables idmapped mounts for erofs, since all dedicated helpers
> for this functionality existsm, so, in this patch we just pass down the
> user_namespace argument from the VFS methods to the relevant helpers.
> 
> Simple idmap example on erofs image:
> 
> 1. mkdir dir
> 2. touch dir/file
> 3. mkfs.erofs erofs.img dir
> 4. mount -t erofs -o loop erofs.img  /mnt/erofs/
> 
> 5. ls -ln /mnt/erofs/
> total 0
> -rw-rw-r-- 1 1000 1000 0 May 17 15:26 file
> 
> 6. mount-idmapped --map-mount b:1000:1001:1 /mnt/erofs/ /mnt/scratch_erofs/
> 
> 7. ls -ln /mnt/scratch_erofs/
> total 0
> -rw-rw-r-- 1 1001 1001 0 May 17 15:26 file
> 
> Reviewed-by: Christian Brauner (Microsoft) <brauner at kernel.org>
> Reviewed-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> Signed-off-by: Chao Yu <chao.yu at oppo.com>
> ---
> v2:
> - fix testcase pointed out by Christian Brauner.
>  fs/erofs/inode.c | 2 +-
>  fs/erofs/super.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> index e8b37ba5e9ad..5320bf52c1ce 100644
> --- a/fs/erofs/inode.c
> +++ b/fs/erofs/inode.c
> @@ -370,7 +370,7 @@ int erofs_getattr(struct user_namespace *mnt_userns, const struct path *path,
>  	stat->attributes_mask |= (STATX_ATTR_COMPRESSED |
>  				  STATX_ATTR_IMMUTABLE);
>  
> -	generic_fillattr(&init_user_ns, inode, stat);
> +	generic_fillattr(mnt_userns, inode, stat);
>  	return 0;
>  }
>  
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 0c4b41130c2f..7dc5f2e8ddee 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -781,7 +781,7 @@ static struct file_system_type erofs_fs_type = {
>  	.name           = "erofs",
>  	.init_fs_context = erofs_init_fs_context,
>  	.kill_sb        = erofs_kill_sb,
> -	.fs_flags       = FS_REQUIRES_DEV,
> +	.fs_flags       = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
>  };
>  MODULE_ALIAS_FS("erofs");
>  
> -- 
> 2.25.1
>