On Mon, Jan 22, 2024 at 12:14 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote:
>
> On Sun, 2024-01-21 at 17:05 +0200, Amir Goldstein wrote:
> > An opaque directory cannot have xwhiteouts, so instead of marking an
> > xwhiteouts directory with a new xattr, overload overlay.opaque xattr
> > for marking both opaque dir ('y') and xwhiteouts dir ('x').
> >
> > This is more efficient as the overlay.opaque xattr is checked during
> > lookup of directory anyway.
> >
> > This also prevents unnecessary checking the xattr when reading a
> > directory without xwhiteouts, i.e. most of the time.
> >
> > Note that the xwhiteouts marker is not checked on the upper layer and
> > on the last layer in lowerstack, where xwhiteouts are not expected.
> >
> > Fixes: bc8df7a3dc03 ("ovl: Add an alternative type of whiteout")
> > Cc: <stable@xxxxxxxxxxxxxxx> # v6.7
> > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > ---
> >
> > Miklos,
> >
> > Alex has reported a problem with your suggested approach of requiring
> > xwhiteouts xattr on layers root dir [1].
> >
> > Following counter proposal, amortizes the cost of checking opaque
> > xattr
> > on directories during lookup to also check for xwhiteouts.
> >
> > This change requires the following change to test overlay/084:
> >
> > --- a/tests/overlay/084
> > +++ b/tests/overlay/084
> > @@ -115,7 +115,8 @@ 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.whiteouts -v "y" $basedir/upper
> > + # overlay.opaque="x" means directory has xwhiteout children
> > + setfattr -n $prefix.overlay.opaque -v "x" $basedir/upper
> > setfattr -n $prefix.overlay.whiteout -v "y"
> > $basedir/upper/hidden
> >
> >
> > Alex,
> >
> > Please let us know if this change is acceptable for composefs.
>
> Yes, this looks very good to me. (Minor comments below)
> I'll do some testing on this.
>
Excellent, I'll be expecting your RVB/Tested-by.
> >
> > Thanks,
> > Amir.
> >
> > [1]
> > https://lore.kernel.org/linux-unionfs/5ee3a210f8f4fc89cb750b3d1a378a0ff0187c9f.camel@xxxxxxxxxx/
> >
> > fs/overlayfs/namei.c | 32 +++++++++++++++++++-------------
> > fs/overlayfs/overlayfs.h | 17 +++++++++++++----
> > fs/overlayfs/ovl_entry.h | 2 ++
> > fs/overlayfs/readdir.c | 5 +++--
> > fs/overlayfs/super.c | 9 +++++++++
> > fs/overlayfs/util.c | 34 ++++++++++++++--------------------
> > 6 files changed, 60 insertions(+), 39 deletions(-)
> >
> > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> > index 984ffdaeed6c..caccf3803796 100644
> > --- a/fs/overlayfs/namei.c
> > +++ b/fs/overlayfs/namei.c
> > @@ -18,10 +18,11 @@
> >
> > struct ovl_lookup_data {
> > struct super_block *sb;
> > - struct vfsmount *mnt;
> > + const struct ovl_layer *layer;
> > struct qstr name;
> > bool is_dir;
> > bool opaque;
> > + bool xwhiteouts;
> > bool stop;
> > bool last;
> > char *redirect;
> > @@ -201,17 +202,13 @@ struct dentry *ovl_decode_real_fh(struct ovl_fs
> > *ofs, struct ovl_fh *fh,
> > return real;
> > }
> >
> > -static bool ovl_is_opaquedir(struct ovl_fs *ofs, const struct path
> > *path)
> > -{
> > - return ovl_path_check_dir_xattr(ofs, path,
> > OVL_XATTR_OPAQUE);
> > -}
> > -
> > static struct dentry *ovl_lookup_positive_unlocked(struct
> > ovl_lookup_data *d,
> > const char *name,
> > struct dentry
> > *base, int len,
> > bool
> > drop_negative)
> > {
> > - struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->mnt),
> > name, base, len);
> > + struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer-
> > >mnt), name,
> > + base, len);
> >
> > if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret-
> > >d_flags))) {
> > if (drop_negative && ret->d_lockref.count == 1) {
> > @@ -232,10 +229,13 @@ static int ovl_lookup_single(struct dentry
> > *base, struct ovl_lookup_data *d,
> > size_t prelen, const char *post,
> > struct dentry **ret, bool
> > drop_negative)
> > {
> > + struct ovl_fs *ofs = OVL_FS(d->sb);
> > struct dentry *this;
> > struct path path;
> > int err;
> > bool last_element = !post[0];
> > + bool is_upper = d->layer->idx == 0;
> > + char val;
> >
> > this = ovl_lookup_positive_unlocked(d, name, base, namelen,
> > drop_negative);
> > if (IS_ERR(this)) {
> > @@ -253,8 +253,8 @@ static int ovl_lookup_single(struct dentry *base,
> > struct ovl_lookup_data *d,
> > }
> >
> > path.dentry = this;
> > - path.mnt = d->mnt;
> > - if (ovl_path_is_whiteout(OVL_FS(d->sb), &path)) {
> > + path.mnt = d->layer->mnt;
> > + if (ovl_path_is_whiteout(ofs, &path)) {
> > d->stop = d->opaque = true;
> > goto put_and_out;
> > }
> > @@ -272,7 +272,7 @@ static int ovl_lookup_single(struct dentry *base,
> > struct ovl_lookup_data *d,
> > d->stop = true;
> > goto put_and_out;
> > }
> > - err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path,
> > NULL);
> > + err = ovl_check_metacopy_xattr(ofs, &path, NULL);
> > if (err < 0)
> > goto out_err;
> >
> > @@ -292,7 +292,11 @@ static int ovl_lookup_single(struct dentry
> > *base, struct ovl_lookup_data *d,
> > if (d->last)
> > goto out;
> >
> > - if (ovl_is_opaquedir(OVL_FS(d->sb), &path)) {
> > + /* overlay.opaque=x means xwhiteouts directory */
> > + val = ovl_get_opaquedir_val(ofs, &path);
> > + if (last_element && !is_upper && val == 'x') {
> > + d->xwhiteouts = true;
> > + } else if (val == 'y') {
> > d->stop = true;
> > if (last_element)
> > d->opaque = true;
> > @@ -1055,7 +1059,7 @@ struct dentry *ovl_lookup(struct inode *dir,
> > struct dentry *dentry,
> > old_cred = ovl_override_creds(dentry->d_sb);
> > upperdir = ovl_dentry_upper(dentry->d_parent);
> > if (upperdir) {
> > - d.mnt = ovl_upper_mnt(ofs);
> > + d.layer = &ofs->layers[0];
> > err = ovl_lookup_layer(upperdir, &d, &upperdentry,
> > true);
> > if (err)
> > goto out;
> > @@ -1111,7 +1115,7 @@ struct dentry *ovl_lookup(struct inode *dir,
> > struct dentry *dentry,
> > else if (d.is_dir || !ofs->numdatalayer)
> > d.last = lower.layer->idx ==
> > ovl_numlower(roe);
> >
> > - d.mnt = lower.layer->mnt;
> > + d.layer = lower.layer;
> > err = ovl_lookup_layer(lower.dentry, &d, &this,
> > false);
> > if (err)
> > goto out_put;
> > @@ -1278,6 +1282,8 @@ struct dentry *ovl_lookup(struct inode *dir,
> > struct dentry *dentry,
> >
> > if (upperopaque)
> > ovl_dentry_set_opaque(dentry);
> > + if (d.xwhiteouts)
> > + ovl_dentry_set_xwhiteouts(dentry);
> >
> > if (upperdentry)
> > ovl_dentry_set_upper_alias(dentry);
> > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> > index 5ba11eb43767..410b3bfc3afc 100644
> > --- a/fs/overlayfs/overlayfs.h
> > +++ b/fs/overlayfs/overlayfs.h
> > @@ -70,6 +70,8 @@ enum ovl_entry_flag {
> > OVL_E_UPPER_ALIAS,
> > OVL_E_OPAQUE,
> > OVL_E_CONNECTED,
> > + /* Lower stack may contain xwhiteout entries */
> > + OVL_E_XWHITEOUTS,
> > };
> >
> > enum {
> > @@ -476,6 +478,8 @@ void ovl_dentry_clear_flag(unsigned long flag,
> > struct dentry *dentry);
> > bool ovl_dentry_test_flag(unsigned long flag, struct dentry
> > *dentry);
> > bool ovl_dentry_is_opaque(struct dentry *dentry);
> > bool ovl_dentry_is_whiteout(struct dentry *dentry);
> > +bool ovl_dentry_is_xwhiteouts(struct dentry *dentry);
> > +void ovl_dentry_set_xwhiteouts(struct dentry *dentry);
> > void ovl_dentry_set_opaque(struct dentry *dentry);
> > bool ovl_dentry_has_upper_alias(struct dentry *dentry);
> > void ovl_dentry_set_upper_alias(struct dentry *dentry);
> > @@ -494,11 +498,10 @@ struct file *ovl_path_open(const struct path
> > *path, int flags);
> > int ovl_copy_up_start(struct dentry *dentry, int flags);
> > void ovl_copy_up_end(struct dentry *dentry);
> > bool ovl_already_copied_up(struct dentry *dentry, int flags);
> > -bool ovl_path_check_dir_xattr(struct ovl_fs *ofs, const struct path
> > *path,
> > - enum ovl_xattr ox);
> > +char ovl_get_dir_xattr_val(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_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
> > const struct path *upperpath);
> >
> > @@ -573,7 +576,13 @@ static inline bool ovl_is_impuredir(struct
> > super_block *sb,
> > .mnt = ovl_upper_mnt(ofs),
> > };
> >
> > - return ovl_path_check_dir_xattr(ofs, &upperpath,
> > OVL_XATTR_IMPURE);
> > + return ovl_get_dir_xattr_val(ofs, &upperpath,
> > OVL_XATTR_IMPURE) == 'y';
> > +}
> > +
> > +static inline char ovl_get_opaquedir_val(struct ovl_fs *ofs,
> > + const struct path *path)
> > +{
> > + return ovl_get_dir_xattr_val(ofs, path, OVL_XATTR_OPAQUE);
> > }
> >
> > static inline bool ovl_redirect_follow(struct ovl_fs *ofs)
> > diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> > index 5fa9c58af65f..0b7b21745ba3 100644
> > --- a/fs/overlayfs/ovl_entry.h
> > +++ b/fs/overlayfs/ovl_entry.h
> > @@ -86,6 +86,8 @@ struct ovl_fs {
> > /* Shared whiteout cache */
> > struct dentry *whiteout;
> > bool no_shared_whiteout;
> > + /* xwhiteouts may exist in lower layers */
> > + bool xwhiteouts;
>
> This comment is a bit off, this is now only used for the root dir.
>
> > /* r/o snapshot of upperdir sb's only taken on volatile
> > mounts */
> > errseq_t errseq;
> > };
> > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> > index e71156baa7bc..edef4e3401de 100644
> > --- a/fs/overlayfs/readdir.c
> > +++ b/fs/overlayfs/readdir.c
> > @@ -165,7 +165,8 @@ static struct ovl_cache_entry
> > *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
> > p->is_upper = rdd->is_upper;
> > p->is_whiteout = false;
> > /* Defer check for overlay.whiteout to ovl_iterate() */
> > - p->check_xwhiteout = rdd->in_xwhiteouts_dir && d_type ==
> > DT_REG;
> > + p->check_xwhiteout = rdd->in_xwhiteouts_dir &&
> > + !rdd->is_upper && d_type == DT_REG;
> >
>
> Maybe we can move the is_upper check to where we set in_xwhiteouts_dir?
>
> > if (d_type == DT_CHR) {
> > p->next_maybe_whiteout = rdd->first_maybe_whiteout;
> > @@ -306,7 +307,7 @@ static inline int ovl_dir_read(const struct path
> > *realpath,
> > return PTR_ERR(realfile);
> >
> > rdd->in_xwhiteouts_dir = rdd->dentry &&
> > - ovl_path_check_xwhiteouts_xattr(OVL_FS(rdd->dentry-
> > >d_sb), realpath);
> > + ovl_dentry_is_xwhiteouts(rdd->dentry);
>
> Now that the xwhiteout flag is on the dentry, it will be set for all
> layers. Maybe we can avoid setting in_whiteouts_dir for the lowermost
> layer?
>
Applied this diff and pushed to the ovl-fixes branch.
Will wait for ACK from Miklos before sending PR.
Thanks,
Amir.
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 0b7b21745ba3..c089e5ff37b5 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -86,7 +86,7 @@ struct ovl_fs {
/* Shared whiteout cache */
struct dentry *whiteout;
bool no_shared_whiteout;
- /* xwhiteouts may exist in lower layers */
+ /* xwhiteouts may exist in lower layer root dirs */
bool xwhiteouts;
/* r/o snapshot of upperdir sb's only taken on volatile mounts */
errseq_t errseq;
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index edef4e3401de..3168e851ca1f 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -165,8 +165,7 @@ static struct ovl_cache_entry
*ovl_cache_entry_new(struct ovl_readdir_data *rdd,
p->is_upper = rdd->is_upper;
p->is_whiteout = false;
/* Defer check for overlay.whiteout to ovl_iterate() */
- p->check_xwhiteout = rdd->in_xwhiteouts_dir &&
- !rdd->is_upper && d_type == DT_REG;
+ p->check_xwhiteout = rdd->in_xwhiteouts_dir && d_type == DT_REG;
if (d_type == DT_CHR) {
p->next_maybe_whiteout = rdd->first_maybe_whiteout;
@@ -306,8 +305,9 @@ 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_dentry_is_xwhiteouts(rdd->dentry);
+ /* No need to check for xwhiteouts in upper and lowermost layers */
+ rdd->in_xwhiteouts_dir = !rdd->is_upper && !rdd->is_lowest &&
+ rdd->dentry && ovl_dentry_is_xwhiteouts(rdd->dentry);
rdd->first_maybe_whiteout = NULL;
rdd->ctx.pos = 0;
