On Fri, Jan 19, 2024 at 12:14 PM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>
> Add a check on each lower layer for the xwhiteout feature. This prevents
> unnecessary checking the overlay.whiteouts xattr when reading a directory
> if this feature is not enabled, i.e. most of the time.
>
> Share the same xattr for the per-directory and the per-layer flag, which
> has the effect that if this is enabled for a layer, then the optimization
> to bypass checking of individual entries does not work on the root of the
> layer. This was deemed better, than having a separate xattr for the layer
> and the directory.
>
> Fixes: bc8df7a3dc03 ("ovl: Add an alternative type of whiteout")
> Cc: <stable@xxxxxxxxxxxxxxx> # v6.7
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> v2:
> - use overlay.whiteouts instead of overlay.feature_xwhiteout
> - move initialization to ovl_get_layers()
> - xwhiteouts can only be enabled on lower layer
>
> fs/overlayfs/namei.c | 10 +++++++---
> fs/overlayfs/overlayfs.h | 7 +++++--
> fs/overlayfs/ovl_entry.h | 2 ++
> fs/overlayfs/readdir.c | 11 ++++++++---
> fs/overlayfs/super.c | 13 +++++++++++++
> fs/overlayfs/util.c | 7 ++++++-
> 6 files changed, 41 insertions(+), 9 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 03bc8d5dfa31..583cf56df66e 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -863,7 +863,8 @@ struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
> * Returns next layer in stack starting from top.
> * Returns -1 if this is the last layer.
> */
> -int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
> +int ovl_path_next(int idx, struct dentry *dentry, struct path *path,
> + const struct ovl_layer **layer)
> {
> struct ovl_entry *oe = OVL_E(dentry);
> struct ovl_path *lowerstack = ovl_lowerstack(oe);
> @@ -871,13 +872,16 @@ int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
> BUG_ON(idx < 0);
> if (idx == 0) {
> ovl_path_upper(dentry, path);
> - if (path->dentry)
> + if (path->dentry) {
> + *layer = &OVL_FS(dentry->d_sb)->layers[0];
> return ovl_numlower(oe) ? 1 : -1;
> + }
> idx++;
> }
> BUG_ON(idx > ovl_numlower(oe));
> path->dentry = lowerstack[idx - 1].dentry;
> - path->mnt = lowerstack[idx - 1].layer->mnt;
> + *layer = lowerstack[idx - 1].layer;
> + path->mnt = (*layer)->mnt;
>
> return (idx < ovl_numlower(oe)) ? idx + 1 : -1;
> }
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 05c3dd597fa8..6359cf5c66ff 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -492,7 +492,9 @@ bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path *path,
> enum ovl_xattr ox);
> bool ovl_path_check_origin_xattr(struct ovl_fs *ofs, const struct path *path);
> bool ovl_path_check_xwhiteout_xattr(struct ovl_fs *ofs, const struct path *path);
> -bool ovl_path_check_xwhiteouts_xattr(struct ovl_fs *ofs, const struct path *path);
> +bool ovl_path_check_xwhiteouts_xattr(struct ovl_fs *ofs,
> + const struct ovl_layer *layer,
> + const struct path *path);
> bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
> const struct path *upperpath);
>
> @@ -674,7 +676,8 @@ int ovl_get_index_name(struct ovl_fs *ofs, struct dentry *origin,
> struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh);
> struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
> struct dentry *origin, bool verify);
> -int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
> +int ovl_path_next(int idx, struct dentry *dentry, struct path *path,
> + const struct ovl_layer **layer);
> int ovl_verify_lowerdata(struct dentry *dentry);
> struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> unsigned int flags);
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index d82d2a043da2..33fcd3d3af30 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -40,6 +40,8 @@ struct ovl_layer {
> int idx;
> /* One fsid per unique underlying sb (upper fsid == 0) */
> int fsid;
> + /* xwhiteouts are enabled on this layer*/
> + bool xwhiteouts;
> };
>
> struct ovl_path {
> diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> index a490fc47c3e7..c2597075e3f8 100644
> --- a/fs/overlayfs/readdir.c
> +++ b/fs/overlayfs/readdir.c
> @@ -305,8 +305,6 @@ static inline int ovl_dir_read(const struct path *realpath,
> if (IS_ERR(realfile))
> return PTR_ERR(realfile);
>
> - rdd->in_xwhiteouts_dir = rdd->dentry &&
> - ovl_path_check_xwhiteouts_xattr(OVL_FS(rdd->dentry->d_sb), realpath);
> rdd->first_maybe_whiteout = NULL;
> rdd->ctx.pos = 0;
> do {
> @@ -359,10 +357,14 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list,
> .is_lowest = false,
> };
> int idx, next;
> + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
> + const struct ovl_layer *layer;
>
> for (idx = 0; idx != -1; idx = next) {
> - next = ovl_path_next(idx, dentry, &realpath);
> + next = ovl_path_next(idx, dentry, &realpath, &layer);
> rdd.is_upper = ovl_dentry_upper(dentry) == realpath.dentry;
> + if (ovl_path_check_xwhiteouts_xattr(ofs, layer, &realpath))
> + rdd.in_xwhiteouts_dir = true;
>
> if (next != -1) {
> err = ovl_dir_read(&realpath, &rdd);
> @@ -568,6 +570,7 @@ static int ovl_dir_read_impure(const struct path *path, struct list_head *list,
> int err;
> struct path realpath;
> struct ovl_cache_entry *p, *n;
> + struct ovl_fs *ofs = OVL_FS(path->dentry->d_sb);
> struct ovl_readdir_data rdd = {
> .ctx.actor = ovl_fill_plain,
> .list = list,
> @@ -577,6 +580,8 @@ static int ovl_dir_read_impure(const struct path *path, struct list_head *list,
> INIT_LIST_HEAD(list);
> *root = RB_ROOT;
> ovl_path_upper(path->dentry, &realpath);
> + if (ovl_path_check_xwhiteouts_xattr(ofs, &ofs->layers[0], &realpath))
> + rdd.in_xwhiteouts_dir = true;
Not needed since we do not support xwhiteouts on upper.
>
> err = ovl_dir_read(&realpath, &rdd);
> if (err)
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index a0967bb25003..04588721eb2a 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1027,6 +1027,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> struct ovl_fs_context_layer *l = &ctx->lower[i];
> struct vfsmount *mnt;
> struct inode *trap;
> + struct path root;
> int fsid;
>
> if (i < nr_merged_lower)
> @@ -1069,6 +1070,16 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> */
> mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
>
> + /*
> + * Check if xwhiteout (xattr whiteout) support is enabled on
> + * this layer.
> + */
> + root.mnt = mnt;
> + root.dentry = mnt->mnt_root;
> + err = ovl_path_getxattr(ofs, &root, OVL_XATTR_XWHITEOUTS, NULL, 0);
> + if (err >= 0)
> + layers[ofs->numlayer].xwhiteouts = true;
> +
> layers[ofs->numlayer].trap = trap;
> layers[ofs->numlayer].mnt = mnt;
> layers[ofs->numlayer].idx = ofs->numlayer;
> @@ -1079,6 +1090,8 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
> l->name = NULL;
> ofs->numlayer++;
> ofs->fs[fsid].is_lower = true;
> +
> +
extra spaces.
> }
>
> /*
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index c3f020ca13a8..6c6e6f5893ea 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -739,11 +739,16 @@ bool ovl_path_check_xwhiteout_xattr(struct ovl_fs *ofs, const struct path *path)
> return res >= 0;
> }
>
> -bool ovl_path_check_xwhiteouts_xattr(struct ovl_fs *ofs, const struct path *path)
> +bool ovl_path_check_xwhiteouts_xattr(struct ovl_fs *ofs,
> + const struct ovl_layer *layer,
> + const struct path *path)
> {
> struct dentry *dentry = path->dentry;
> int res;
>
> + if (!layer->xwhiteouts)
> + return false;
> +
> /* xattr.whiteouts must be a directory */
> if (!d_is_dir(dentry))
> return false;
> --
> 2.43.0
>
Do you want me to fix/test and send this to Linus?
Alex, can we add your RVB to v2?
Thanks,
Amir.
