Re: [PATCH] ovl: require xwhiteout feature flag on layer roots

On Thu, Jan 18, 2024 at 12:41 PM Miklos Szeredi mszeredi@redhat.com 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@vger.kernel.org # v6.7 Signed-off-by: Miklos Szeredi mszeredi@redhat.com

---

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.