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.
>
> 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?
> rdd->first_maybe_whiteout = NULL;
> rdd->ctx.pos = 0;
> do {
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 4ab66e3d4cff..81f045025c96 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1026,6 +1026,7 @@ 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)
> @@ -1068,6 +1069,12 @@ static int ovl_get_layers(struct super_block
> *sb, struct ovl_fs *ofs,
> */
> mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
>
> + /* overlay.opaque=x means xwhiteouts directory */
> + root.mnt = mnt;
> + root.dentry = mnt->mnt_root;
> + if (ovl_get_opaquedir_val(ofs, &root) == 'x')
> + ofs->xwhiteouts = true;
> +
> layers[ofs->numlayer].trap = trap;
> layers[ofs->numlayer].mnt = mnt;
> layers[ofs->numlayer].idx = ofs->numlayer;
> @@ -1272,6 +1279,8 @@ static struct dentry *ovl_get_root(struct
> super_block *sb,
>
> /* Root is always merge -> can have whiteouts */
> ovl_set_flag(OVL_WHITEOUTS, d_inode(root));
> + if (OVL_FS(sb)->xwhiteouts)
> + ovl_dentry_set_flag(OVL_E_XWHITEOUTS, root);
> ovl_dentry_set_flag(OVL_E_CONNECTED, root);
> ovl_set_upperdata(d_inode(root));
> ovl_inode_init(d_inode(root), &oip, ino, fsid);
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index 0217094c23ea..fb622995fb28 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -456,6 +456,16 @@ bool ovl_dentry_is_whiteout(struct dentry
> *dentry)
> return !dentry->d_inode && ovl_dentry_is_opaque(dentry);
> }
>
> +bool ovl_dentry_is_xwhiteouts(struct dentry *dentry)
> +{
> + return ovl_dentry_test_flag(OVL_E_XWHITEOUTS, dentry);
> +}
> +
> +void ovl_dentry_set_xwhiteouts(struct dentry *dentry)
> +{
> + ovl_dentry_set_flag(OVL_E_XWHITEOUTS, dentry);
> +}
> +
> void ovl_dentry_set_opaque(struct dentry *dentry)
> {
> ovl_dentry_set_flag(OVL_E_OPAQUE, dentry);
> @@ -739,19 +749,6 @@ 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)
> -{
> - struct dentry *dentry = path->dentry;
> - int res;
> -
> - /* xattr.whiteouts must be a directory */
> - if (!d_is_dir(dentry))
> - return false;
> -
> - res = ovl_path_getxattr(ofs, path, OVL_XATTR_XWHITEOUTS,
> NULL, 0);
> - return res >= 0;
> -}
> -
> /*
> * Load persistent uuid from xattr into s_uuid if found, or store a
> new
> * random generated value in s_uuid and in xattr.
> @@ -811,20 +808,17 @@ bool ovl_init_uuid_xattr(struct super_block
> *sb, struct ovl_fs *ofs,
> return false;
> }
>
> -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)
> {
> int res;
> char val;
>
> if (!d_is_dir(path->dentry))
> - return false;
> + return 0;
>
> res = ovl_path_getxattr(ofs, path, ox, &val, 1);
> - if (res == 1 && val == 'y')
> - return true;
> -
> - return false;
> + return res == 1 ? val : 0;
> }
>
> #define OVL_XATTR_OPAQUE_POSTFIX "opaque"
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-=-=
Alexander Larsson Red Hat,
Inc
alexl@xxxxxxxxxx alexander.larsson@xxxxxxxxx
He's a deeply religious small-town paranormal investigator searching
for
his wife's true killer. She's a strong-willed French-Canadian single
mother operating on the wrong side of the law. They fight crime!
