On Tue, Jul 31, 2018 at 12:37 PM, zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote:
> Index feature is backward read-only compatible becasue it only affect
> the upper layer, and old kernel (which not support this feature) may
> corrupt the relationship between files in upper dir and index dir when
> change the copied-up linked files.
>
> If the index feature is enabled, kernel will create an index dir in the
> work base dir, so this patch check and set upper layer's index feature
> when overlayfs get or create the index dir.
>
> Signed-off-by: zhangyi (F) <yi.zhang@xxxxxxxxxx>
> ---
> fs/overlayfs/overlayfs.h | 4 +++-
> fs/overlayfs/super.c | 11 +++++++++--
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 7ed8ed49266f..21a41c12168c 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -59,7 +59,8 @@ struct ovl_d_feature {
> #define OVL_FEATURE_COMPAT_SUPP (0)
> #define OVL_FEATURE_COMPAT_UNKNOWN (~OVL_FEATURE_COMPAT_SUPP)
>
> -#define OVL_FEATURE_RO_COMPAT_SUPP (0)
> +#define OVL_FEATURE_RO_COMPAT_INDEX (1 << 0)
> +#define OVL_FEATURE_RO_COMPAT_SUPP (OVL_FEATURE_RO_COMPAT_INDEX)
> #define OVL_FEATURE_RO_COMPAT_UNKNOWN (~OVL_FEATURE_RO_COMPAT_SUPP)
>
> #define OVL_FEATURE_INCOMPAT_REDIRECT_DIR (1 << 0)
> @@ -130,6 +131,7 @@ static inline int ovl_set_feature_##name(struct ovl_fs *ofs) \
> OVL_FEATURE_INCOMPAT_##flagname); \
> } \
>
> +OVL_FEATURE_RO_COMPAT_FUNCS(index, INDEX)
> OVL_FEATURE_INCOMPAT_FUNCS(redirect_dir, REDIRECT_DIR)
>
> /*
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index a5bbbddf741c..197329f7d284 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1443,8 +1443,15 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> if (err)
> goto out_free_oe;
>
> - /* Force r/o mount with no index dir */
> - if (!ofs->indexdir) {
> + if (ofs->indexdir) {
> + /* Set index feature if index dir exists */
> + if (!ovl_has_feature_index(ofs->upper_layer)) {
> + err = ovl_set_feature_index(ofs);
ovl_set_feature_index() is enough. it should test the bit internally.
Thanks,
Amir.
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