On Thu, 17 Jun 2021 at 17:22, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> Instead, if any of the fileattr flags of interest exist on the lower
> inode, we store them in overlay.xflags xattr on the upper inode and we
> we read the flags from xattr on lookup and on fileattr_get().
Calling this xflags, especially near fileattr code, makes it easy to
confuse with fsx_xflags. Can we find a more distinctive name?
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index aec353a2dc80..d66e51b9c347 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -162,7 +162,8 @@ int ovl_getattr(struct user_namespace *mnt_userns, const struct path *path,
> enum ovl_path_type type;
> struct path realpath;
> const struct cred *old_cred;
> - bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
> + struct inode *inode = d_inode(dentry);
> + bool is_dir = S_ISDIR(inode->i_mode);
> int fsid = 0;
> int err;
> bool metacopy_blocks = false;
> @@ -175,6 +176,10 @@ int ovl_getattr(struct user_namespace *mnt_userns, const struct path *path,
> if (err)
> goto out;
>
> + /* Report immutable/append-only STATX flags */
> + if (ovl_test_flag(OVL_XFLAGS, inode))
> + ovl_fill_xflags(inode, stat, NULL);
> +
Filesystems are doing these transformations: (already down one from
before fileattr)
internal flags -> statx->attributes
internal flags -> inode->i_flags
internal flags <-> fa->flags or fa->fsx_xflags
To further improve this situation the statx filling could be moved to
generic code based on i_flags. I'm not asking you to convert all
filesystems (though that would be nice), but adding the helpers and
using them here would be a good first step.
> @@ -639,6 +642,174 @@ int ovl_set_impure(struct dentry *dentry, struct dentry *upperdentry)
> return err;
> }
>
> +
> +/*
> + * Overlayfs stores immutable/append-only attributes in overlay.xflags xattr.
> + * If upper inode does have those fileattr flags set (i.e. from old kernel),
> + * overlayfs does not clear them on fileattr_get(), but it will clear them on
> + * fileattr_set().
> + */
> +#define OVL_XFLAG(c, x) \
> + { c, S_ ## x, FS_ ## x ## _FL, FS_XFLAG_ ## x, STATX_ATTR_ ## x }
> +
> +struct ovl_xflag {
> + char code;
> + u32 i_flag;
> + u32 fs_flag;
> + u32 fsx_flag;
> + u64 statx_attr;
> +} const ovl_xflags[] = {
> + OVL_XFLAG('a', APPEND),
> + OVL_XFLAG('i', IMMUTABLE),
> +};
This would be really nice for a dozen flags, but for two...
My guess is that many lines of code could be saved by un-generalizing this.
> +/* Set inode flags and xflags xattr from fileattr */
> +int ovl_set_xflags(struct inode *inode, struct dentry *upper,
> + struct fileattr *fa)
> +{
> + struct ovl_fs *ofs = OVL_FS(inode->i_sb);
> + char buf[OVL_XFLAGS_NUM];
> + int len, err = 0;
> +
> + BUILD_BUG_ON(OVL_XFLAGS_NUM >= OVL_XFLAGS_MAX);
> + len = ovl_xflags_to_buf(inode, buf, OVL_XFLAGS_NUM, fa);
> +
> + /*
> + * Do not fail when upper doesn't support xattrs, but also do not
> + * mask out the xattr xflags from real fileattr to continue
> + * supporting fileattr_set() on fs without xattr support.
> + * Remove xattr if it exist and all flags are cleared.
> + */
Does this matter in practice? I.e. is there any filesystem with
immutable/append attribute but not xattr that could be an upper layer?
If yes, then this could end up as a copy-up regression (failure to
copy up files having immutable/append).
Thanks,
Miklos
