Re: [RFC PATCH v2 4/9] ovl: add helper funcs to set upper layer feature set

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Jul 31, 2018 at 12:37 PM, zhangyi (F) <yi.zhang@huawei.com> wrote:
> overlayfs will want to add the upper layer's feature bitset if some
> overlay file system features were set. For example: redirect dir feature
> will be set when user rename a lower/merge dir if redirect dir feature
> is enabled. So add helper functions to set feature sets to the upper
> layer for future use.
>
> This patch introduce helper functions only, does not set any feature
> bits.
>
> Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
> ---
>  fs/overlayfs/feature.c   | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/overlayfs/overlayfs.h | 46 ++++++++++++++++++++++++++
>  fs/overlayfs/ovl_entry.h |  2 ++
>  fs/overlayfs/super.c     |  1 +
>  4 files changed, 134 insertions(+)
>
> diff --git a/fs/overlayfs/feature.c b/fs/overlayfs/feature.c
> index fac4d7544475..7c66e71bdd98 100644
> --- a/fs/overlayfs/feature.c
> +++ b/fs/overlayfs/feature.c
> @@ -10,6 +10,8 @@
>
>  #include <linux/fs.h>
>  #include <linux/xattr.h>
> +#include <linux/mount.h>
> +#include <linux/ratelimit.h>
>  #include "overlayfs.h"
>
>  /*
> @@ -63,6 +65,89 @@ static struct ovl_d_feature *ovl_get_feature(struct dentry *realroot)
>  }
>
>  /*
> + * Set overlay features to the upper root dir.
> + *
> + * @upper_layer: overlay upper layer information,
> + * @upper: upper root dentry.
> + *
> + * Return 0 if success, error number otherwise.
> + */
> +static int ovl_set_feature(struct ovl_layer *upper_layer,
> +                          struct dentry *upper)
> +{
> +       struct vfsmount *upper_mnt = upper_layer->mnt;
> +       struct ovl_d_feature odf = {};
> +       int err;
> +
> +       odf.magic = OVL_FEATURE_MAGIC;
> +       odf.compat = cpu_to_be64(upper_layer->compat);
> +       odf.ro_compat = cpu_to_be64(upper_layer->ro_compat);
> +       odf.incompat = cpu_to_be64(upper_layer->incompat);
> +
> +       err = mnt_want_write(upper_mnt);
> +       if (err)
> +               return err;
> +
> +       err = ovl_do_setxattr(upper, OVL_XATTR_FEATURE,
> +                             &odf, sizeof(odf), 0);
> +       if (err)
> +               pr_err_ratelimited("overlayfs: failed to set features (%i)\n", err);
> +
> +       mnt_drop_write(upper_mnt);
> +       return err;
> +}
> +
> +/*
> + * Add feature bit mask to the upper root dir.
> + *
> + * @ofs: overlay filesystem information
> + * @type: feature set type, compat, ro compat or incompat
> + * @mask: new features mask want to add
> + *
> + * Return 0 if success, error number otherwise.
> + */
> +int ovl_set_upper_feature(struct ovl_fs *ofs,
> +                         enum ovl_feature_type type,
> +                         u64 mask)
> +{
> +       struct ovl_layer *upper_layer = ofs->upper_layer;
> +       u64 *features;
> +       int err;
> +
> +       if (!upper_layer)
> +               return -EINVAL;
> +
> +       switch (type) {
> +       case OVL_FEATURE_COMPAT:
> +               features = &upper_layer->compat;
> +               break;
> +       case OVL_FEATURE_RO_COMPAT:
> +               features = &upper_layer->ro_compat;
> +               break;
> +       case OVL_FEATURE_INCOMPAT:
> +               features = &upper_layer->incompat;
> +               break;
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       spin_lock(&upper_layer->lock);
> +       if ((*features) & mask) {
> +               spin_unlock(&upper_layer->lock);
> +               return 0;
> +       }
> +
> +       (*features) |= mask;
> +       spin_unlock(&upper_layer->lock);
> +

Seems like you can move the above test and set into
ovl_set_feature() and you can also use upperdir->d_lock
and don't need to introduce a new spinlock for this.

Thanks,
Amir.