On Thu, Jan 18, 2024 at 12:41 PM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>
> Add a check on each 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.
Does it really have a significant cost or do you just not like the
unneeded check?
IIRC, we anyway check for ORIGIN xattr and IMPURE xattr on
readdir.
>
> Fixes: bc8df7a3dc03 ("ovl: Add an alternative type of whiteout")
> Cc: <stable@xxxxxxxxxxxxxxx> # v6.7
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
>
> Hi Alex,
>
> Can you please test this in your environment?
>
> I xwhiteout test in xfstests needs this tweak:
>
> --- a/tests/overlay/084
> +++ b/tests/overlay/084
> @@ -115,6 +115,7 @@ do_test_xwhiteout()
>
> mkdir -p $basedir/lower $basedir/upper $basedir/work
> touch $basedir/lower/regular $basedir/lower/hidden $basedir/upper/hidden
> + setfattr -n $prefix.overlay.feature_xwhiteout -v "y" $basedir/upper
> setfattr -n $prefix.overlay.whiteouts -v "y" $basedir/upper
> setfattr -n $prefix.overlay.whiteout -v "y" $basedir/upper/hidden
>
>
> Thanks,
> Miklos
>
> fs/overlayfs/namei.c | 10 +++++++---
> fs/overlayfs/overlayfs.h | 8 ++++++--
> fs/overlayfs/ovl_entry.h | 2 ++
> fs/overlayfs/readdir.c | 11 ++++++++---
> fs/overlayfs/super.c | 13 ++++++++++++-
> fs/overlayfs/util.c | 9 ++++++++-
> 6 files changed, 43 insertions(+), 10 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..991eb5d5c66c 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -51,6 +51,7 @@ enum ovl_xattr {
> OVL_XATTR_PROTATTR,
> OVL_XATTR_XWHITEOUT,
> OVL_XATTR_XWHITEOUTS,
> + OVL_XATTR_FEATURE_XWHITEOUT,
Can we not add a new OVL_XATTR_FEATURE_XWHITEOUT xattr.
Setting OVL_XATTR_XWHITEOUTS on directories with xwhiteouts is
anyway the responsibility of the layer composer.
Let's just require the layer composer to set OVL_XATTR_XWHITEOUTS
on the layer root even if it does not have any immediate xwhiteout
children as "layer may have xwhiteouts" indication. ok?
> };
>
> enum ovl_inode_flag {
> @@ -492,7 +493,9 @@ 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 +677,8 @@ 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..51729e614f5a 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 feature_xwhiteout;
> };
>
> 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;
>
> err = ovl_dir_read(&realpath, &rdd);
> if (err)
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index a0967bb25003..4e507ab780f3 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1291,7 +1291,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
> struct ovl_entry *oe;
> struct ovl_layer *layers;
> struct cred *cred;
> - int err;
> + int err, i;
>
> err = -EIO;
> if (WARN_ON(fc->user_ns != current_user_ns()))
> @@ -1414,6 +1414,17 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
> if (err)
> goto out_free_oe;
>
> + for (i = 0; i < ofs->numlayer; i++) {
> + struct path path = { .mnt = layers[i].mnt };
> +
> + if (path.mnt) {
> + path.dentry = path.mnt->mnt_root;
> + err = ovl_path_getxattr(ofs, &path, OVL_XATTR_FEATURE_XWHITEOUT, NULL, 0);
> + if (err >= 0)
> + layers[i].feature_xwhiteout = true;
Any reason not to do this in ovl_get_layers() when adding the layer?
Thanks,
Amir.
