Re: [RFC PATCH 1/2] ovl: skip checking lower file's write permisson on truncate

[Miklos Szeredi <miklos@szeredi.hu>]

On Sat, 24 Apr 2021 at 16:04, Chengguang Xu <cgxu519@mykernel.net> wrote:
>
> Lower files may be shared in overlayfs so strictly checking write
> perssmion on lower file will cause interferes between different
> overlayfs instances.

How so?

i_writecount on lower inode is not modified by overlayfs (at least not
in this codepath).  Which means that there should be no interference
between overlayfs instances sharing a lower directory tree.

Thanks,
Miklos



>
> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
> ---
>  fs/overlayfs/inode.c | 6 ------
>  1 file changed, 6 deletions(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 28c71978eb2e..17d1add0af1a 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -31,12 +31,6 @@ int ovl_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>                 goto out;
>
>         if (attr->ia_valid & ATTR_SIZE) {
> -               struct inode *realinode = d_inode(ovl_dentry_real(dentry));
> -
> -               err = -ETXTBSY;
> -               if (atomic_read(&realinode->i_writecount) < 0)
> -                       goto out_drop_write;
> -
>                 /* Truncate should trigger data copy up as well */
>                 full_copy_up = true;
>         }
> --
> 2.27.0
>
>