// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Copyright (C) 2011 Novell Inc.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/namei.h>
#include <linux/file.h>
#include <linux/xattr.h>
#include <linux/rbtree.h>
#include <linux/security.h>
#include <linux/cred.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

struct ovl_cache_entry {
        unsigned int len;
        unsigned int type;
        u64 real_ino;
        u64 ino;
        struct list_head l_node;
        struct rb_node node;
        struct ovl_cache_entry *next_maybe_whiteout;
        bool is_upper;
        bool is_whiteout;
        char name[];
};

struct ovl_dir_cache {
        long refcount;
        u64 version;
        struct list_head entries;
        struct rb_root root;
};

struct ovl_readdir_data {
        struct dir_context ctx;
        struct dentry *dentry;
        bool is_lowest;
        struct rb_root *root;
        struct list_head *list;
        struct list_head middle;
        struct ovl_cache_entry *first_maybe_whiteout;
        int count;
        int err;
        bool is_upper;
        bool d_type_supported;
};

struct ovl_dir_file {
        bool is_real;
        bool is_upper;
        struct ovl_dir_cache *cache;
        struct list_head *cursor;
        struct file *realfile;
        struct file *upperfile;
};

static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
{
        return rb_entry(n, struct ovl_cache_entry, node);
}

static bool ovl_cache_entry_find_link(const char *name, int len,
                                      struct rb_node ***link,
                                      struct rb_node **parent)
{
        bool found = false;
        struct rb_node **newp = *link;

        while (!found && *newp) {
                int cmp;
                struct ovl_cache_entry *tmp;

                *parent = *newp;
                tmp = ovl_cache_entry_from_node(*newp);
                cmp = strncmp(name, tmp->name, len);
                if (cmp > 0)
                        newp = &tmp->node.rb_right;
                else if (cmp < 0 || len < tmp->len)
                        newp = &tmp->node.rb_left;
                else
                        found = true;
        }
        *link = newp;

        return found;
}

static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
                                                    const char *name, int len)
{
        struct rb_node *node = root->rb_node;
        int cmp;

        while (node) {
                struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);

                cmp = strncmp(name, p->name, len);
                if (cmp > 0)
                        node = p->node.rb_right;
                else if (cmp < 0 || len < p->len)
                        node = p->node.rb_left;
                else
                        return p;
        }

        return NULL;
}

static bool ovl_calc_d_ino(struct ovl_readdir_data *rdd,
                           struct ovl_cache_entry *p)
{
        /* Don't care if not doing ovl_iter() */
        if (!rdd->dentry)
                return false;

        /* Always recalc d_ino when remapping lower inode numbers */
        if (ovl_xino_bits(rdd->dentry->d_sb))
                return true;

        /* Always recalc d_ino for parent */
        if (strcmp(p->name, "..") == 0)
                return true;

        /* If this is lower, then native d_ino will do */
        if (!rdd->is_upper)
                return false;

        /*
         * Recalc d_ino for '.' and for all entries if dir is impure (contains
         * copied up entries)
         */
        if ((p->name[0] == '.' && p->len == 1) ||
            ovl_test_flag(OVL_IMPURE, d_inode(rdd->dentry)))
                return true;

        return false;
}

static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
                                                   const char *name, int len,
                                                   u64 ino, unsigned int d_type)
{
        struct ovl_cache_entry *p;
        size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);

        p = kmalloc(size, GFP_KERNEL);
        if (!p)
                return NULL;

        memcpy(p->name, name, len);
        p->name[len] = '\0';
        p->len = len;
        p->type = d_type;
        p->real_ino = ino;
        p->ino = ino;
        /* Defer setting d_ino for upper entry to ovl_iterate() */
        if (ovl_calc_d_ino(rdd, p))
                p->ino = 0;
        p->is_upper = rdd->is_upper;
        p->is_whiteout = false;

        if (d_type == DT_CHR) {
                p->next_maybe_whiteout = rdd->first_maybe_whiteout;
                rdd->first_maybe_whiteout = p;
        }
        return p;
}

static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
                                  const char *name, int len, u64 ino,
                                  unsigned int d_type)
{
        struct rb_node **newp = &rdd->root->rb_node;
        struct rb_node *parent = NULL;
        struct ovl_cache_entry *p;

        if (ovl_cache_entry_find_link(name, len, &newp, &parent))
                return 0;

        p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
        if (p == NULL) {
                rdd->err = -ENOMEM;
                return -ENOMEM;
        }

        list_add_tail(&p->l_node, rdd->list);
        rb_link_node(&p->node, parent, newp);
        rb_insert_color(&p->node, rdd->root);

        return 0;
}

static int ovl_fill_lowest(struct ovl_readdir_data *rdd,
                           const char *name, int namelen,
                           loff_t offset, u64 ino, unsigned int d_type)
{
        struct ovl_cache_entry *p;

        p = ovl_cache_entry_find(rdd->root, name, namelen);
        if (p) {
                list_move_tail(&p->l_node, &rdd->middle);
        } else {
                p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
                if (p == NULL)
                        rdd->err = -ENOMEM;
                else
                        list_add_tail(&p->l_node, &rdd->middle);
        }

        return rdd->err;
}

void ovl_cache_free(struct list_head *list)
{
        struct ovl_cache_entry *p;
        struct ovl_cache_entry *n;

        list_for_each_entry_safe(p, n, list, l_node)
                kfree(p);

        INIT_LIST_HEAD(list);
}

void ovl_dir_cache_free(struct inode *inode)
{
        struct ovl_dir_cache *cache = ovl_dir_cache(inode);

        if (cache) {
                ovl_cache_free(&cache->entries);
                kfree(cache);
        }
}

static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
{
        struct ovl_dir_cache *cache = od->cache;

        WARN_ON(cache->refcount <= 0);
        cache->refcount--;
        if (!cache->refcount) {
                if (ovl_dir_cache(d_inode(dentry)) == cache)
                        ovl_set_dir_cache(d_inode(dentry), NULL);

                ovl_cache_free(&cache->entries);
                kfree(cache);
        }
}

static int ovl_fill_merge(struct dir_context *ctx, const char *name,
                          int namelen, loff_t offset, u64 ino,
                          unsigned int d_type)
{
        struct ovl_readdir_data *rdd =
                container_of(ctx, struct ovl_readdir_data, ctx);

        rdd->count++;
        if (!rdd->is_lowest)
                return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
        else
                return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
}

static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
{
        int err;
        struct ovl_cache_entry *p;
        struct dentry *dentry;
        const struct cred *old_cred;

        old_cred = ovl_override_creds(rdd->dentry->d_sb);

        err = down_write_killable(&dir->d_inode->i_rwsem);
        if (!err) {
                while (rdd->first_maybe_whiteout) {
                        p = rdd->first_maybe_whiteout;
                        rdd->first_maybe_whiteout = p->next_maybe_whiteout;
                        dentry = lookup_one_len(p->name, dir, p->len);
                        if (!IS_ERR(dentry)) {
                                p->is_whiteout = ovl_is_whiteout(dentry);
                                dput(dentry);
                        }
                }
                inode_unlock(dir->d_inode);
        }
        revert_creds(old_cred);

        return err;
}

static inline int ovl_dir_read(struct path *realpath,
                               struct ovl_readdir_data *rdd)
{
        struct file *realfile;
        int err;

        realfile = ovl_path_open(realpath, O_RDONLY | O_LARGEFILE);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        rdd->first_maybe_whiteout = NULL;
        rdd->ctx.pos = 0;
        do {
                rdd->count = 0;
                rdd->err = 0;
                err = iterate_dir(realfile, &rdd->ctx);
                if (err >= 0)
                        err = rdd->err;
        } while (!err && rdd->count);

        if (!err && rdd->first_maybe_whiteout && rdd->dentry)
                err = ovl_check_whiteouts(realpath->dentry, rdd);

        fput(realfile);

        return err;
}

static void ovl_dir_reset(struct file *file)
{
        struct ovl_dir_file *od = file->private_data;
        struct ovl_dir_cache *cache = od->cache;
        struct dentry *dentry = file->f_path.dentry;
        bool is_real;

        if (cache && ovl_dentry_version_get(dentry) != cache->version) {
                ovl_cache_put(od, dentry);
                od->cache = NULL;
                od->cursor = NULL;
        }
        is_real = ovl_dir_is_real(dentry);
        if (od->is_real != is_real) {
                /* is_real can only become false when dir is copied up */
                if (WARN_ON(is_real))
                        return;
                od->is_real = false;
        }
}

static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list,
        struct rb_root *root)
{
        int err;
        struct path realpath;
        struct ovl_readdir_data rdd = {
                .ctx.actor = ovl_fill_merge,
                .dentry = dentry,
                .list = list,
                .root = root,
                .is_lowest = false,
        };
        int idx, next;

        for (idx = 0; idx != -1; idx = next) {
                next = ovl_path_next(idx, dentry, &realpath);
                rdd.is_upper = ovl_dentry_upper(dentry) == realpath.dentry;

                if (next != -1) {
                        err = ovl_dir_read(&realpath, &rdd);
                        if (err)
                                break;
                } else {
                        /*
                         * Insert lowest layer entries before upper ones, this
                         * allows offsets to be reasonably constant
                         */
                        list_add(&rdd.middle, rdd.list);
                        rdd.is_lowest = true;
                        err = ovl_dir_read(&realpath, &rdd);
                        list_del(&rdd.middle);
                }
        }
        return err;
}

static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
{
        struct list_head *p;
        loff_t off = 0;

        list_for_each(p, &od->cache->entries) {
                if (off >= pos)
                        break;
                off++;
        }
        /* Cursor is safe since the cache is stable */
        od->cursor = p;
}

static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
{
        int res;
        struct ovl_dir_cache *cache;

        cache = ovl_dir_cache(d_inode(dentry));
        if (cache && ovl_dentry_version_get(dentry) == cache->version) {
                WARN_ON(!cache->refcount);
                cache->refcount++;
                return cache;
        }
        ovl_set_dir_cache(d_inode(dentry), NULL);

        cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
        if (!cache)
                return ERR_PTR(-ENOMEM);

        cache->refcount = 1;
        INIT_LIST_HEAD(&cache->entries);
        cache->root = RB_ROOT;

        res = ovl_dir_read_merged(dentry, &cache->entries, &cache->root);
        if (res) {
                ovl_cache_free(&cache->entries);
                kfree(cache);
                return ERR_PTR(res);
        }

        cache->version = ovl_dentry_version_get(dentry);
        ovl_set_dir_cache(d_inode(dentry), cache);

        return cache;
}

/* Map inode number to lower fs unique range */
static u64 ovl_remap_lower_ino(u64 ino, int xinobits, int fsid,
                               const char *name, int namelen, bool warn)
{
        unsigned int xinoshift = 64 - xinobits;

        if (unlikely(ino >> xinoshift)) {
                if (warn) {
                        pr_warn_ratelimited("d_ino too big (%.*s, ino=%llu, xinobits=%d)\n",
                                            namelen, name, ino, xinobits);
                }
                return ino;
        }

        /*
         * The lowest xinobit is reserved for mapping the non-peresistent inode
         * numbers range, but this range is only exposed via st_ino, not here.
         */
        return ino | ((u64)fsid) << (xinoshift + 1);
}

/*
 * Set d_ino for upper entries. Non-upper entries should always report
 * the uppermost real inode ino and should not call this function.
 *
 * When not all layer are on same fs, report real ino also for upper.
 *
 * When all layers are on the same fs, and upper has a reference to
 * copy up origin, call vfs_getattr() on the overlay entry to make
 * sure that d_ino will be consistent with st_ino from stat(2).
 */
static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)

{
        struct dentry *dir = path->dentry;
        struct dentry *this = NULL;
        enum ovl_path_type type;
        u64 ino = p->real_ino;
        int xinobits = ovl_xino_bits(dir->d_sb);
        int err = 0;

        if (!ovl_same_dev(dir->d_sb))
                goto out;

        if (p->name[0] == '.') {
                if (p->len == 1) {
                        this = dget(dir);
                        goto get;
                }
                if (p->len == 2 && p->name[1] == '.') {
                        /* we shall not be moved */
                        this = dget(dir->d_parent);
                        goto get;
                }
        }
        this = lookup_one_len(p->name, dir, p->len);
        if (IS_ERR_OR_NULL(this) || !this->d_inode) {
                /* Mark a stale entry */
                p->is_whiteout = true;
                if (IS_ERR(this)) {
                        err = PTR_ERR(this);
                        this = NULL;
                        goto fail;
                }
                goto out;
        }

get:
        type = ovl_path_type(this);
        if (OVL_TYPE_ORIGIN(type)) {
                struct kstat stat;
                struct path statpath = *path;

                statpath.dentry = this;
                err = vfs_getattr(&statpath, &stat, STATX_INO, 0);
                if (err)
                        goto fail;

                /*
                 * Directory inode is always on overlay st_dev.
                 * Non-dir with ovl_same_dev() could be on pseudo st_dev in case
                 * of xino bits overflow.
                 */
                WARN_ON_ONCE(S_ISDIR(stat.mode) &&
                             dir->d_sb->s_dev != stat.dev);
                ino = stat.ino;
        } else if (xinobits && !OVL_TYPE_UPPER(type)) {
                ino = ovl_remap_lower_ino(ino, xinobits,
                                          ovl_layer_lower(this)->fsid,
                                          p->name, p->len,
                                          ovl_xino_warn(dir->d_sb));
        }

out:
        p->ino = ino;
        dput(this);
        return err;

fail:
        pr_warn_ratelimited("failed to look up (%s) for ino (%i)\n",
                            p->name, err);
        goto out;
}

static int ovl_fill_plain(struct dir_context *ctx, const char *name,
                          int namelen, loff_t offset, u64 ino,
                          unsigned int d_type)
{
        struct ovl_cache_entry *p;
        struct ovl_readdir_data *rdd =
                container_of(ctx, struct ovl_readdir_data, ctx);

        rdd->count++;
        p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
        if (p == NULL) {
                rdd->err = -ENOMEM;
                return -ENOMEM;
        }
        list_add_tail(&p->l_node, rdd->list);

        return 0;
}

static int ovl_dir_read_impure(struct path *path,  struct list_head *list,
                               struct rb_root *root)
{
        int err;
        struct path realpath;
        struct ovl_cache_entry *p, *n;
        struct ovl_readdir_data rdd = {
                .ctx.actor = ovl_fill_plain,
                .list = list,
                .root = root,
        };

        INIT_LIST_HEAD(list);
        *root = RB_ROOT;
        ovl_path_upper(path->dentry, &realpath);

        err = ovl_dir_read(&realpath, &rdd);
        if (err)
                return err;

        list_for_each_entry_safe(p, n, list, l_node) {
                if (strcmp(p->name, ".") != 0 &&
                    strcmp(p->name, "..") != 0) {
                        err = ovl_cache_update_ino(path, p);
                        if (err)
                                return err;
                }
                if (p->ino == p->real_ino) {
                        list_del(&p->l_node);
                        kfree(p);
                } else {
                        struct rb_node **newp = &root->rb_node;
                        struct rb_node *parent = NULL;

                        if (WARN_ON(ovl_cache_entry_find_link(p->name, p->len,
                                                              &newp, &parent)))
                                return -EIO;

                        rb_link_node(&p->node, parent, newp);
                        rb_insert_color(&p->node, root);
                }
        }
        return 0;
}

static struct ovl_dir_cache *ovl_cache_get_impure(struct path *path)
{
        int res;
        struct dentry *dentry = path->dentry;
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct ovl_dir_cache *cache;

        cache = ovl_dir_cache(d_inode(dentry));
        if (cache && ovl_dentry_version_get(dentry) == cache->version)
                return cache;

        /* Impure cache is not refcounted, free it here */
        ovl_dir_cache_free(d_inode(dentry));
        ovl_set_dir_cache(d_inode(dentry), NULL);

        cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
        if (!cache)
                return ERR_PTR(-ENOMEM);

        res = ovl_dir_read_impure(path, &cache->entries, &cache->root);
        if (res) {
                ovl_cache_free(&cache->entries);
                kfree(cache);
                return ERR_PTR(res);
        }
        if (list_empty(&cache->entries)) {
                /*
                 * A good opportunity to get rid of an unneeded "impure" flag.
                 * Removing the "impure" xattr is best effort.
                 */
                if (!ovl_want_write(dentry)) {
                        ovl_do_removexattr(ofs, ovl_dentry_upper(dentry),
                                           OVL_XATTR_IMPURE);
                        ovl_drop_write(dentry);
                }
                ovl_clear_flag(OVL_IMPURE, d_inode(dentry));
                kfree(cache);
                return NULL;
        }

        cache->version = ovl_dentry_version_get(dentry);
        ovl_set_dir_cache(d_inode(dentry), cache);

        return cache;
}

struct ovl_readdir_translate {
        struct dir_context *orig_ctx;
        struct ovl_dir_cache *cache;
        struct dir_context ctx;
        u64 parent_ino;
        int fsid;
        int xinobits;
        bool xinowarn;
};

static int ovl_fill_real(struct dir_context *ctx, const char *name,
                           int namelen, loff_t offset, u64 ino,
                           unsigned int d_type)
{
        struct ovl_readdir_translate *rdt =
                container_of(ctx, struct ovl_readdir_translate, ctx);
        struct dir_context *orig_ctx = rdt->orig_ctx;

        if (rdt->parent_ino && strcmp(name, "..") == 0) {
                ino = rdt->parent_ino;
        } else if (rdt->cache) {
                struct ovl_cache_entry *p;

                p = ovl_cache_entry_find(&rdt->cache->root, name, namelen);
                if (p)
                        ino = p->ino;
        } else if (rdt->xinobits) {
                ino = ovl_remap_lower_ino(ino, rdt->xinobits, rdt->fsid,
                                          name, namelen, rdt->xinowarn);
        }

        return orig_ctx->actor(orig_ctx, name, namelen, offset, ino, d_type);
}

static bool ovl_is_impure_dir(struct file *file)
{
        struct ovl_dir_file *od = file->private_data;
        struct inode *dir = d_inode(file->f_path.dentry);

        /*
         * Only upper dir can be impure, but if we are in the middle of
         * iterating a lower real dir, dir could be copied up and marked
         * impure. We only want the impure cache if we started iterating
         * a real upper dir to begin with.
         */
        return od->is_upper && ovl_test_flag(OVL_IMPURE, dir);

}

static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
{
        int err;
        struct ovl_dir_file *od = file->private_data;
        struct dentry *dir = file->f_path.dentry;
        const struct ovl_layer *lower_layer = ovl_layer_lower(dir);
        struct ovl_readdir_translate rdt = {
                .ctx.actor = ovl_fill_real,
                .orig_ctx = ctx,
                .xinobits = ovl_xino_bits(dir->d_sb),
                .xinowarn = ovl_xino_warn(dir->d_sb),
        };

        if (rdt.xinobits && lower_layer)
                rdt.fsid = lower_layer->fsid;

        if (OVL_TYPE_MERGE(ovl_path_type(dir->d_parent))) {
                struct kstat stat;
                struct path statpath = file->f_path;

                statpath.dentry = dir->d_parent;
                err = vfs_getattr(&statpath, &stat, STATX_INO, 0);
                if (err)
                        return err;

                WARN_ON_ONCE(dir->d_sb->s_dev != stat.dev);
                rdt.parent_ino = stat.ino;
        }

        if (ovl_is_impure_dir(file)) {
                rdt.cache = ovl_cache_get_impure(&file->f_path);
                if (IS_ERR(rdt.cache))
                        return PTR_ERR(rdt.cache);
        }

        err = iterate_dir(od->realfile, &rdt.ctx);
        ctx->pos = rdt.ctx.pos;

        return err;
}


static int ovl_iterate(struct file *file, struct dir_context *ctx)
{
        struct ovl_dir_file *od = file->private_data;
        struct dentry *dentry = file->f_path.dentry;
        struct ovl_cache_entry *p;
        const struct cred *old_cred;
        int err;

        old_cred = ovl_override_creds(dentry->d_sb);
        if (!ctx->pos)
                ovl_dir_reset(file);

        if (od->is_real) {
                /*
                 * If parent is merge, then need to adjust d_ino for '..', if
                 * dir is impure then need to adjust d_ino for copied up
                 * entries.
                 */
                if (ovl_xino_bits(dentry->d_sb) ||
                    (ovl_same_fs(dentry->d_sb) &&
                     (ovl_is_impure_dir(file) ||
                      OVL_TYPE_MERGE(ovl_path_type(dentry->d_parent))))) {
                        err = ovl_iterate_real(file, ctx);
                } else {
                        err = iterate_dir(od->realfile, ctx);
                }
                goto out;
        }

        if (!od->cache) {
                struct ovl_dir_cache *cache;

                cache = ovl_cache_get(dentry);
                err = PTR_ERR(cache);
                if (IS_ERR(cache))
                        goto out;

                od->cache = cache;
                ovl_seek_cursor(od, ctx->pos);
        }

        while (od->cursor != &od->cache->entries) {
                p = list_entry(od->cursor, struct ovl_cache_entry, l_node);
                if (!p->is_whiteout) {
                        if (!p->ino) {
                                err = ovl_cache_update_ino(&file->f_path, p);
                                if (err)
                                        goto out;
                        }
                }
                /* ovl_cache_update_ino() sets is_whiteout on stale entry */
                if (!p->is_whiteout) {
                        if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
                                break;
                }
                od->cursor = p->l_node.next;
                ctx->pos++;
        }
        err = 0;
out:
        revert_creds(old_cred);
        return err;
}

static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
{
        loff_t res;
        struct ovl_dir_file *od = file->private_data;

        inode_lock(file_inode(file));
        if (!file->f_pos)
                ovl_dir_reset(file);

        if (od->is_real) {
                res = vfs_llseek(od->realfile, offset, origin);
                file->f_pos = od->realfile->f_pos;
        } else {
                res = -EINVAL;

                switch (origin) {
                case SEEK_CUR:
                        offset += file->f_pos;
                        break;
                case SEEK_SET:
                        break;
                default:
                        goto out_unlock;
                }
                if (offset < 0)
                        goto out_unlock;

                if (offset != file->f_pos) {
                        file->f_pos = offset;
                        if (od->cache)
                                ovl_seek_cursor(od, offset);
                }
                res = offset;
        }
out_unlock:
        inode_unlock(file_inode(file));

        return res;
}

static struct file *ovl_dir_open_realfile(const struct file *file,
                                          struct path *realpath)
{
        struct file *res;
        const struct cred *old_cred;

        old_cred = ovl_override_creds(file_inode(file)->i_sb);
        res = ovl_path_open(realpath, O_RDONLY | (file->f_flags & O_LARGEFILE));
        revert_creds(old_cred);

        return res;
}

/*
 * Like ovl_real_fdget(), returns upperfile if dir was copied up since open.
 * Unlike ovl_real_fdget(), this caches upperfile in file->private_data.
 *
 * TODO: use same abstract type for file->private_data of dir and file so
 * upperfile could also be cached for files as well.
 */
struct file *ovl_dir_real_file(const struct file *file, bool want_upper)
{

        struct ovl_dir_file *od = file->private_data;
        struct dentry *dentry = file->f_path.dentry;
        struct file *old, *realfile = od->realfile;

        if (!OVL_TYPE_UPPER(ovl_path_type(dentry)))
                return want_upper ? NULL : realfile;

        /*
         * Need to check if we started out being a lower dir, but got copied up
         */
        if (!od->is_upper) {
                realfile = READ_ONCE(od->upperfile);
                if (!realfile) {
                        struct path upperpath;

                        ovl_path_upper(dentry, &upperpath);
                        realfile = ovl_dir_open_realfile(file, &upperpath);
                        if (IS_ERR(realfile))
                                return realfile;

                        old = cmpxchg_release(&od->upperfile, NULL, realfile);
                        if (old) {
                                fput(realfile);
                                realfile = old;
                        }
                }
        }

        return realfile;
}

static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
                         int datasync)
{
        struct file *realfile;
        int err;

        err = ovl_sync_status(OVL_FS(file->f_path.dentry->d_sb));
        if (err <= 0)
                return err;

        realfile = ovl_dir_real_file(file, true);
        err = PTR_ERR_OR_ZERO(realfile);

        /* Nothing to sync for lower */
        if (!realfile || err)
                return err;

        return vfs_fsync_range(realfile, start, end, datasync);
}

static int ovl_dir_release(struct inode *inode, struct file *file)
{
        struct ovl_dir_file *od = file->private_data;

        if (od->cache) {
                inode_lock(inode);
                ovl_cache_put(od, file->f_path.dentry);
                inode_unlock(inode);
        }
        fput(od->realfile);
        if (od->upperfile)
                fput(od->upperfile);
        kfree(od);

        return 0;
}

static int ovl_dir_open(struct inode *inode, struct file *file)
{
        struct path realpath;
        struct file *realfile;
        struct ovl_dir_file *od;
        enum ovl_path_type type;

        od = kzalloc(sizeof(struct ovl_dir_file), GFP_KERNEL);
        if (!od)
                return -ENOMEM;

        type = ovl_path_real(file->f_path.dentry, &realpath);
        realfile = ovl_dir_open_realfile(file, &realpath);
        if (IS_ERR(realfile)) {
                kfree(od);
                return PTR_ERR(realfile);
        }
        od->realfile = realfile;
        od->is_real = ovl_dir_is_real(file->f_path.dentry);
        od->is_upper = OVL_TYPE_UPPER(type);
        file->private_data = od;

        return 0;
}

const struct file_operations ovl_dir_operations = {
        .read           = generic_read_dir,
        .open           = ovl_dir_open,
        .iterate        = ovl_iterate,
        .llseek         = ovl_dir_llseek,
        .fsync          = ovl_dir_fsync,
        .release        = ovl_dir_release,
};

int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
{
        int err;
        struct ovl_cache_entry *p, *n;
        struct rb_root root = RB_ROOT;
        const struct cred *old_cred;

        old_cred = ovl_override_creds(dentry->d_sb);
        err = ovl_dir_read_merged(dentry, list, &root);
        revert_creds(old_cred);
        if (err)
                return err;

        err = 0;

        list_for_each_entry_safe(p, n, list, l_node) {
                /*
                 * Select whiteouts in upperdir, they should
                 * be cleared when deleting this directory.
                 */
                if (p->is_whiteout) {
                        if (p->is_upper)
                                continue;
                        goto del_entry;
                }

                if (p->name[0] == '.') {
                        if (p->len == 1)
                                goto del_entry;
                        if (p->len == 2 && p->name[1] == '.')
                                goto del_entry;
                }
                err = -ENOTEMPTY;
                break;

del_entry:
                list_del(&p->l_node);
                kfree(p);
        }

        return err;
}

void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
{
        struct ovl_cache_entry *p;

        inode_lock_nested(upper->d_inode, I_MUTEX_CHILD);
        list_for_each_entry(p, list, l_node) {
                struct dentry *dentry;

                if (WARN_ON(!p->is_whiteout || !p->is_upper))
                        continue;

                dentry = lookup_one_len(p->name, upper, p->len);
                if (IS_ERR(dentry)) {
                        pr_err("lookup '%s/%.*s' failed (%i)\n",
                               upper->d_name.name, p->len, p->name,
                               (int) PTR_ERR(dentry));
                        continue;
                }
                if (dentry->d_inode)
                        ovl_cleanup(upper->d_inode, dentry);
                dput(dentry);
        }
        inode_unlock(upper->d_inode);
}

static int ovl_check_d_type(struct dir_context *ctx, const char *name,
                          int namelen, loff_t offset, u64 ino,
                          unsigned int d_type)
{
        struct ovl_readdir_data *rdd =
                container_of(ctx, struct ovl_readdir_data, ctx);

        /* Even if d_type is not supported, DT_DIR is returned for . and .. */
        if (!strncmp(name, ".", namelen) || !strncmp(name, "..", namelen))
                return 0;

        if (d_type != DT_UNKNOWN)
                rdd->d_type_supported = true;

        return 0;
}

/*
 * Returns 1 if d_type is supported, 0 not supported/unknown. Negative values
 * if error is encountered.
 */
int ovl_check_d_type_supported(struct path *realpath)
{
        int err;
        struct ovl_readdir_data rdd = {
                .ctx.actor = ovl_check_d_type,
                .d_type_supported = false,
        };

        err = ovl_dir_read(realpath, &rdd);
        if (err)
                return err;

        return rdd.d_type_supported;
}

#define OVL_INCOMPATDIR_NAME "incompat"

static int ovl_workdir_cleanup_recurse(struct path *path, int level)
{
        int err;
        struct inode *dir = path->dentry->d_inode;
        LIST_HEAD(list);
        struct rb_root root = RB_ROOT;
        struct ovl_cache_entry *p;
        struct ovl_readdir_data rdd = {
                .ctx.actor = ovl_fill_merge,
                .dentry = NULL,
                .list = &list,
                .root = &root,
                .is_lowest = false,
        };
        bool incompat = false;

        /*
         * The "work/incompat" directory is treated specially - if it is not
         * empty, instead of printing a generic error and mounting read-only,
         * we will error about incompat features and fail the mount.
         *
         * When called from ovl_indexdir_cleanup(), path->dentry->d_name.name
         * starts with '#'.
         */
        if (level == 2 &&
            !strcmp(path->dentry->d_name.name, OVL_INCOMPATDIR_NAME))
                incompat = true;

        err = ovl_dir_read(path, &rdd);
        if (err)
                goto out;

        inode_lock_nested(dir, I_MUTEX_PARENT);
        list_for_each_entry(p, &list, l_node) {
                struct dentry *dentry;

                if (p->name[0] == '.') {
                        if (p->len == 1)
                                continue;
                        if (p->len == 2 && p->name[1] == '.')
                                continue;
                } else if (incompat) {
                        pr_err("overlay with incompat feature '%s' cannot be mounted\n",
                                p->name);
                        err = -EINVAL;
                        break;
                }
                dentry = lookup_one_len(p->name, path->dentry, p->len);
                if (IS_ERR(dentry))
                        continue;
                if (dentry->d_inode)
                        err = ovl_workdir_cleanup(dir, path->mnt, dentry, level);
                dput(dentry);
                if (err)
                        break;
        }
        inode_unlock(dir);
out:
        ovl_cache_free(&list);
        return err;
}

int ovl_workdir_cleanup(struct inode *dir, struct vfsmount *mnt,
                         struct dentry *dentry, int level)
{
        int err;

        if (!d_is_dir(dentry) || level > 1) {
                return ovl_cleanup(dir, dentry);
        }

        err = ovl_do_rmdir(dir, dentry);
        if (err) {
                struct path path = { .mnt = mnt, .dentry = dentry };

                inode_unlock(dir);
                err = ovl_workdir_cleanup_recurse(&path, level + 1);
                inode_lock_nested(dir, I_MUTEX_PARENT);
                if (!err)
                        err = ovl_cleanup(dir, dentry);
        }

        return err;
}

int ovl_indexdir_cleanup(struct ovl_fs *ofs)
{
        int err;
        struct dentry *indexdir = ofs->indexdir;
        struct dentry *index = NULL;
        struct inode *dir = indexdir->d_inode;
        struct path path = { .mnt = ovl_upper_mnt(ofs), .dentry = indexdir };
        LIST_HEAD(list);
        struct rb_root root = RB_ROOT;
        struct ovl_cache_entry *p;
        struct ovl_readdir_data rdd = {
                .ctx.actor = ovl_fill_merge,
                .dentry = NULL,
                .list = &list,
                .root = &root,
                .is_lowest = false,
        };

        err = ovl_dir_read(&path, &rdd);
        if (err)
                goto out;

        inode_lock_nested(dir, I_MUTEX_PARENT);
        list_for_each_entry(p, &list, l_node) {
                if (p->name[0] == '.') {
                        if (p->len == 1)
                                continue;
                        if (p->len == 2 && p->name[1] == '.')
                                continue;
                }
                index = lookup_one_len(p->name, indexdir, p->len);
                if (IS_ERR(index)) {
                        err = PTR_ERR(index);
                        index = NULL;
                        break;
                }
                /* Cleanup leftover from index create/cleanup attempt */
                if (index->d_name.name[0] == '#') {
                        err = ovl_workdir_cleanup(dir, path.mnt, index, 1);
                        if (err)
                                break;
                        goto next;
                }
                err = ovl_verify_index(ofs, index);
                if (!err) {
                        goto next;
                } else if (err == -ESTALE) {
                        /* Cleanup stale index entries */
                        err = ovl_cleanup(dir, index);
                } else if (err != -ENOENT) {
                        /*
                         * Abort mount to avoid corrupting the index if
                         * an incompatible index entry was found or on out
                         * of memory.
                         */
                        break;
                } else if (ofs->config.nfs_export) {
                        /*
                         * Whiteout orphan index to block future open by
                         * handle after overlay nlink dropped to zero.
                         */
                        err = ovl_cleanup_and_whiteout(ofs, dir, index);
                } else {
                        /* Cleanup orphan index entries */
                        err = ovl_cleanup(dir, index);
                }

                if (err)
                        break;

next:
                dput(index);
                index = NULL;
        }
        dput(index);
        inode_unlock(dir);
out:
        ovl_cache_free(&list);
        if (err)
                pr_err("failed index dir cleanup (%i)\n", err);
        return err;
}