/*
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/uuid.h>
#include <linux/namei.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

int ovl_want_write(struct dentry *dentry)
{
        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
        return mnt_want_write(ovl_upper_mnt(ofs));
}

void ovl_drop_write(struct dentry *dentry)
{
        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
        mnt_drop_write(ovl_upper_mnt(ofs));
}

struct dentry *ovl_workdir(struct dentry *dentry)
{
        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
        return ofs->workdir;
}

const struct cred *ovl_override_creds(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return override_creds(ofs->creator_cred);
}

/*
 * Check if underlying fs supports file handles and try to determine encoding
 * type, in order to deduce maximum inode number used by fs.
 *
 * Return 0 if file handles are not supported.
 * Return 1 (FILEID_INO32_GEN) if fs uses the default 32bit inode encoding.
 * Return -1 if fs uses a non default encoding with unknown inode size.
 */
int ovl_can_decode_fh(struct super_block *sb)
{
        if (!capable(CAP_DAC_READ_SEARCH))
                return 0;

        if (!sb->s_export_op || !sb->s_export_op->fh_to_dentry)
                return 0;

        return sb->s_export_op->encode_fh ? -1 : FILEID_INO32_GEN;
}

struct dentry *ovl_indexdir(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return ofs->indexdir;
}

/* Index all files on copy up. For now only enabled for NFS export */
bool ovl_index_all(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return ofs->config.nfs_export && ofs->config.index;
}

/* Verify lower origin on lookup. For now only enabled for NFS export */
bool ovl_verify_lower(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return ofs->config.nfs_export && ofs->config.index;
}

struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
        size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
        struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);

        if (oe)
                oe->numlower = numlower;

        return oe;
}

bool ovl_dentry_remote(struct dentry *dentry)
{
        return dentry->d_flags &
                (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
}

void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
                             unsigned int mask)
{
        struct ovl_entry *oe = OVL_E(dentry);
        unsigned int i, flags = 0;

        if (upperdentry)
                flags |= upperdentry->d_flags;
        for (i = 0; i < oe->numlower; i++)
                flags |= oe->lowerstack[i].dentry->d_flags;

        spin_lock(&dentry->d_lock);
        dentry->d_flags &= ~mask;
        dentry->d_flags |= flags & mask;
        spin_unlock(&dentry->d_lock);
}

bool ovl_dentry_weird(struct dentry *dentry)
{
        return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
                                  DCACHE_MANAGE_TRANSIT |
                                  DCACHE_OP_HASH |
                                  DCACHE_OP_COMPARE);
}

enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;
        enum ovl_path_type type = 0;

        if (ovl_dentry_upper(dentry)) {
                type = __OVL_PATH_UPPER;

                /*
                 * Non-dir dentry can hold lower dentry of its copy up origin.
                 */
                if (oe->numlower) {
                        if (ovl_test_flag(OVL_CONST_INO, d_inode(dentry)))
                                type |= __OVL_PATH_ORIGIN;
                        if (d_is_dir(dentry) ||
                            !ovl_has_upperdata(d_inode(dentry)))
                                type |= __OVL_PATH_MERGE;
                }
        } else {
                if (oe->numlower > 1)
                        type |= __OVL_PATH_MERGE;
        }
        return type;
}

void ovl_path_upper(struct dentry *dentry, struct path *path)
{
        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;

        path->mnt = ovl_upper_mnt(ofs);
        path->dentry = ovl_dentry_upper(dentry);
}

void ovl_path_lower(struct dentry *dentry, struct path *path)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        if (oe->numlower) {
                path->mnt = oe->lowerstack[0].layer->mnt;
                path->dentry = oe->lowerstack[0].dentry;
        } else {
                *path = (struct path) { };
        }
}

void ovl_path_lowerdata(struct dentry *dentry, struct path *path)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        if (oe->numlower) {
                path->mnt = oe->lowerstack[oe->numlower - 1].layer->mnt;
                path->dentry = oe->lowerstack[oe->numlower - 1].dentry;
        } else {
                *path = (struct path) { };
        }
}

enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
{
        enum ovl_path_type type = ovl_path_type(dentry);

        if (!OVL_TYPE_UPPER(type))
                ovl_path_lower(dentry, path);
        else
                ovl_path_upper(dentry, path);

        return type;
}

struct dentry *ovl_dentry_upper(struct dentry *dentry)
{
        return ovl_upperdentry_dereference(OVL_I(d_inode(dentry)));
}

struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        return oe->numlower ? oe->lowerstack[0].dentry : NULL;
}

const struct ovl_layer *ovl_layer_lower(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        return oe->numlower ? oe->lowerstack[0].layer : NULL;
}

/*
 * ovl_dentry_lower() could return either a data dentry or metacopy dentry
 * dependig on what is stored in lowerstack[0]. At times we need to find
 * lower dentry which has data (and not metacopy dentry). This helper
 * returns the lower data dentry.
 */
struct dentry *ovl_dentry_lowerdata(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        return oe->numlower ? oe->lowerstack[oe->numlower - 1].dentry : NULL;
}

struct dentry *ovl_dentry_real(struct dentry *dentry)
{
        return ovl_dentry_upper(dentry) ?: ovl_dentry_lower(dentry);
}

struct dentry *ovl_i_dentry_upper(struct inode *inode)
{
        return ovl_upperdentry_dereference(OVL_I(inode));
}

struct inode *ovl_inode_upper(struct inode *inode)
{
        struct dentry *upperdentry = ovl_i_dentry_upper(inode);

        return upperdentry ? d_inode(upperdentry) : NULL;
}

struct inode *ovl_inode_lower(struct inode *inode)
{
        return OVL_I(inode)->lower;
}

struct inode *ovl_inode_real(struct inode *inode)
{
        return ovl_inode_upper(inode) ?: ovl_inode_lower(inode);
}

/* Return inode which contains lower data. Do not return metacopy */
struct inode *ovl_inode_lowerdata(struct inode *inode)
{
        if (WARN_ON(!S_ISREG(inode->i_mode)))
                return NULL;

        return OVL_I(inode)->lowerdata ?: ovl_inode_lower(inode);
}

/* Return real inode which contains data. Does not return metacopy inode */
struct inode *ovl_inode_realdata(struct inode *inode)
{
        struct inode *upperinode;

        upperinode = ovl_inode_upper(inode);
        if (upperinode && ovl_has_upperdata(inode))
                return upperinode;

        return ovl_inode_lowerdata(inode);
}

struct ovl_dir_cache *ovl_dir_cache(struct inode *inode)
{
        return OVL_I(inode)->cache;
}

void ovl_set_dir_cache(struct inode *inode, struct ovl_dir_cache *cache)
{
        OVL_I(inode)->cache = cache;
}

void ovl_dentry_set_flag(unsigned long flag, struct dentry *dentry)
{
        set_bit(flag, &OVL_E(dentry)->flags);
}

void ovl_dentry_clear_flag(unsigned long flag, struct dentry *dentry)
{
        clear_bit(flag, &OVL_E(dentry)->flags);
}

bool ovl_dentry_test_flag(unsigned long flag, struct dentry *dentry)
{
        return test_bit(flag, &OVL_E(dentry)->flags);
}

bool ovl_dentry_is_opaque(struct dentry *dentry)
{
        return ovl_dentry_test_flag(OVL_E_OPAQUE, dentry);
}

bool ovl_dentry_is_whiteout(struct dentry *dentry)
{
        return !dentry->d_inode && ovl_dentry_is_opaque(dentry);
}

void ovl_dentry_set_opaque(struct dentry *dentry)
{
        ovl_dentry_set_flag(OVL_E_OPAQUE, dentry);
}

/*
 * For hard links and decoded file handles, it's possible for ovl_dentry_upper()
 * to return positive, while there's no actual upper alias for the inode.
 * Copy up code needs to know about the existence of the upper alias, so it
 * can't use ovl_dentry_upper().
 */
bool ovl_dentry_has_upper_alias(struct dentry *dentry)
{
        return ovl_dentry_test_flag(OVL_E_UPPER_ALIAS, dentry);
}

void ovl_dentry_set_upper_alias(struct dentry *dentry)
{
        ovl_dentry_set_flag(OVL_E_UPPER_ALIAS, dentry);
}

static bool ovl_should_check_upperdata(struct inode *inode)
{
        if (!S_ISREG(inode->i_mode))
                return false;

        if (!ovl_inode_lower(inode))
                return false;

        return true;
}

bool ovl_has_upperdata(struct inode *inode)
{
        if (!ovl_should_check_upperdata(inode))
                return true;

        if (!ovl_test_flag(OVL_UPPERDATA, inode))
                return false;
        /*
         * Pairs with smp_wmb() in ovl_set_upperdata(). Main user of
         * ovl_has_upperdata() is ovl_copy_up_meta_inode_data(). Make sure
         * if setting of OVL_UPPERDATA is visible, then effects of writes
         * before that are visible too.
         */
        smp_rmb();
        return true;
}

void ovl_set_upperdata(struct inode *inode)
{
        /*
         * Pairs with smp_rmb() in ovl_has_upperdata(). Make sure
         * if OVL_UPPERDATA flag is visible, then effects of write operations
         * before it are visible as well.
         */
        smp_wmb();
        ovl_set_flag(OVL_UPPERDATA, inode);
}

/* Caller should hold ovl_inode->lock */
bool ovl_dentry_needs_data_copy_up_locked(struct dentry *dentry, int flags)
{
        if (!ovl_open_flags_need_copy_up(flags))
                return false;

        return !ovl_test_flag(OVL_UPPERDATA, d_inode(dentry));
}

bool ovl_dentry_needs_data_copy_up(struct dentry *dentry, int flags)
{
        if (!ovl_open_flags_need_copy_up(flags))
                return false;

        return !ovl_has_upperdata(d_inode(dentry));
}

bool ovl_redirect_dir(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return ofs->config.redirect_dir && !ofs->noxattr;
}

const char *ovl_dentry_get_redirect(struct dentry *dentry)
{
        return OVL_I(d_inode(dentry))->redirect;
}

void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect)
{
        struct ovl_inode *oi = OVL_I(d_inode(dentry));

        kfree(oi->redirect);
        oi->redirect = redirect;
}

void ovl_inode_update(struct inode *inode, struct dentry *upperdentry)
{
        struct inode *upperinode = d_inode(upperdentry);

        WARN_ON(OVL_I(inode)->__upperdentry);

        /*
         * Make sure upperdentry is consistent before making it visible
         */
        smp_wmb();
        OVL_I(inode)->__upperdentry = upperdentry;
        if (inode_unhashed(inode)) {
                inode->i_private = upperinode;
                __insert_inode_hash(inode, (unsigned long) upperinode);
        }
}

static void ovl_dentry_version_inc(struct dentry *dentry, bool impurity)
{
        struct inode *inode = d_inode(dentry);

        WARN_ON(!inode_is_locked(inode));
        /*
         * Version is used by readdir code to keep cache consistent.  For merge
         * dirs all changes need to be noted.  For non-merge dirs, cache only
         * contains impure (ones which have been copied up and have origins)
         * entries, so only need to note changes to impure entries.
         */
        if (OVL_TYPE_MERGE(ovl_path_type(dentry)) || impurity)
                OVL_I(inode)->version++;
}

void ovl_dir_modified(struct dentry *dentry, bool impurity)
{
        /* Copy mtime/ctime */
        ovl_copyattr(d_inode(ovl_dentry_upper(dentry)), d_inode(dentry));

        ovl_dentry_version_inc(dentry, impurity);
}

u64 ovl_dentry_version_get(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        WARN_ON(!inode_is_locked(inode));
        return OVL_I(inode)->version;
}

bool ovl_is_whiteout(struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        return inode && IS_WHITEOUT(inode);
}

struct file *ovl_path_open(struct path *path, int flags)
{
        struct inode *inode = d_inode(path->dentry);
        int err, acc_mode;

        if (flags & ~(O_ACCMODE | O_LARGEFILE))
                BUG();

        switch (flags & O_ACCMODE) {
        case O_RDONLY:
                acc_mode = MAY_READ;
                break;
        case O_WRONLY:
                acc_mode = MAY_WRITE;
                break;
        default:
                BUG();
        }

        err = inode_permission(inode, acc_mode | MAY_OPEN);
        if (err)
                return ERR_PTR(err);

        /* O_NOATIME is an optimization, don't fail if not permitted */
        if (inode_owner_or_capable(inode))
                flags |= O_NOATIME;

        return dentry_open(path, flags, current_cred());
}

/* Caller should hold ovl_inode->lock */
static bool ovl_already_copied_up_locked(struct dentry *dentry, int flags)
{
        bool disconnected = dentry->d_flags & DCACHE_DISCONNECTED;

        if (ovl_dentry_upper(dentry) &&
            (ovl_dentry_has_upper_alias(dentry) || disconnected) &&
            !ovl_dentry_needs_data_copy_up_locked(dentry, flags))
                return true;

        return false;
}

bool ovl_already_copied_up(struct dentry *dentry, int flags)
{
        bool disconnected = dentry->d_flags & DCACHE_DISCONNECTED;

        /*
         * Check if copy-up has happened as well as for upper alias (in
         * case of hard links) is there.
         *
         * Both checks are lockless:
         *  - false negatives: will recheck under oi->lock
         *  - false positives:
         *    + ovl_dentry_upper() uses memory barriers to ensure the
         *      upper dentry is up-to-date
         *    + ovl_dentry_has_upper_alias() relies on locking of
         *      upper parent i_rwsem to prevent reordering copy-up
         *      with rename.
         */
        if (ovl_dentry_upper(dentry) &&
            (ovl_dentry_has_upper_alias(dentry) || disconnected) &&
            !ovl_dentry_needs_data_copy_up(dentry, flags))
                return true;

        return false;
}

int ovl_copy_up_start(struct dentry *dentry, int flags)
{
        struct inode *inode = d_inode(dentry);
        int err;

        err = ovl_inode_lock_interruptible(inode);
        if (!err && ovl_already_copied_up_locked(dentry, flags)) {
                err = 1; /* Already copied up */
                ovl_inode_unlock(inode);
        }

        return err;
}

void ovl_copy_up_end(struct dentry *dentry)
{
        ovl_inode_unlock(d_inode(dentry));
}

bool ovl_check_origin_xattr(struct ovl_fs *ofs, struct dentry *dentry)
{
        int res;

        res = ovl_do_getxattr(ofs, dentry, OVL_XATTR_ORIGIN, NULL, 0);

        /* Zero size value means "copied up but origin unknown" */
        if (res >= 0)
                return true;

        return false;
}

bool ovl_check_dir_xattr(struct super_block *sb, struct dentry *dentry,
                         enum ovl_xattr ox)
{
        int res;
        char val;

        if (!d_is_dir(dentry))
                return false;

        res = ovl_do_getxattr(OVL_FS(sb), dentry, ox, &val, 1);
        if (res == 1 && val == 'y')
                return true;

        return false;
}

#define OVL_XATTR_OPAQUE_POSTFIX        "opaque"
#define OVL_XATTR_REDIRECT_POSTFIX      "redirect"
#define OVL_XATTR_ORIGIN_POSTFIX        "origin"
#define OVL_XATTR_IMPURE_POSTFIX        "impure"
#define OVL_XATTR_NLINK_POSTFIX         "nlink"
#define OVL_XATTR_UPPER_POSTFIX         "upper"
#define OVL_XATTR_METACOPY_POSTFIX      "metacopy"

#define OVL_XATTR_TAB_ENTRY(x) \
        [x] = { [false] = OVL_XATTR_TRUSTED_PREFIX x ## _POSTFIX, \
                [true] = OVL_XATTR_USER_PREFIX x ## _POSTFIX }

const char *const ovl_xattr_table[][2] = {
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_OPAQUE),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_REDIRECT),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_ORIGIN),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_IMPURE),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_NLINK),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_UPPER),
        OVL_XATTR_TAB_ENTRY(OVL_XATTR_METACOPY),
};

int ovl_check_setxattr(struct dentry *dentry, struct dentry *upperdentry,
                       enum ovl_xattr ox, const void *value, size_t size,
                       int xerr)
{
        int err;
        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;

        if (ofs->noxattr)
                return xerr;

        err = ovl_do_setxattr(ofs, upperdentry, ox, value, size);

        if (err == -EOPNOTSUPP) {
                pr_warn("cannot set %s xattr on upper\n", ovl_xattr(ofs, ox));
                ofs->noxattr = true;
                return xerr;
        }

        return err;
}

int ovl_set_impure(struct dentry *dentry, struct dentry *upperdentry)
{
        int err;

        if (ovl_test_flag(OVL_IMPURE, d_inode(dentry)))
                return 0;

        /*
         * Do not fail when upper doesn't support xattrs.
         * Upper inodes won't have origin nor redirect xattr anyway.
         */
        err = ovl_check_setxattr(dentry, upperdentry, OVL_XATTR_IMPURE,
                                 "y", 1, 0);
        if (!err)
                ovl_set_flag(OVL_IMPURE, d_inode(dentry));

        return err;
}

void ovl_set_flag(unsigned long flag, struct inode *inode)
{
        set_bit(flag, &OVL_I(inode)->flags);
}

void ovl_clear_flag(unsigned long flag, struct inode *inode)
{
        clear_bit(flag, &OVL_I(inode)->flags);
}

bool ovl_test_flag(unsigned long flag, struct inode *inode)
{
        return test_bit(flag, &OVL_I(inode)->flags);
}

/**
 * Caller must hold a reference to inode to prevent it from being freed while
 * it is marked inuse.
 */
bool ovl_inuse_trylock(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        bool locked = false;

        spin_lock(&inode->i_lock);
        if (!(inode->i_state & I_OVL_INUSE)) {
                inode->i_state |= I_OVL_INUSE;
                locked = true;
        }
        spin_unlock(&inode->i_lock);

        return locked;
}

void ovl_inuse_unlock(struct dentry *dentry)
{
        if (dentry) {
                struct inode *inode = d_inode(dentry);

                spin_lock(&inode->i_lock);
                WARN_ON(!(inode->i_state & I_OVL_INUSE));
                inode->i_state &= ~I_OVL_INUSE;
                spin_unlock(&inode->i_lock);
        }
}

bool ovl_is_inuse(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        bool inuse;

        spin_lock(&inode->i_lock);
        inuse = (inode->i_state & I_OVL_INUSE);
        spin_unlock(&inode->i_lock);

        return inuse;
}

/*
 * Does this overlay dentry need to be indexed on copy up?
 */
bool ovl_need_index(struct dentry *dentry)
{
        struct dentry *lower = ovl_dentry_lower(dentry);

        if (!lower || !ovl_indexdir(dentry->d_sb))
                return false;

        /* Index all files for NFS export and consistency verification */
        if (ovl_index_all(dentry->d_sb))
                return true;

        /* Index only lower hardlinks on copy up */
        if (!d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
                return true;

        return false;
}

/* Caller must hold OVL_I(inode)->lock */
static void ovl_cleanup_index(struct dentry *dentry)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct dentry *indexdir = ovl_indexdir(dentry->d_sb);
        struct inode *dir = indexdir->d_inode;
        struct dentry *lowerdentry = ovl_dentry_lower(dentry);
        struct dentry *upperdentry = ovl_dentry_upper(dentry);
        struct dentry *index = NULL;
        struct inode *inode;
        struct qstr name = { };
        int err;

        err = ovl_get_index_name(ofs, lowerdentry, &name);
        if (err)
                goto fail;

        inode = d_inode(upperdentry);
        if (!S_ISDIR(inode->i_mode) && inode->i_nlink != 1) {
                pr_warn_ratelimited("cleanup linked index (%pd2, ino=%lu, nlink=%u)\n",
                                    upperdentry, inode->i_ino, inode->i_nlink);
                /*
                 * We either have a bug with persistent union nlink or a lower
                 * hardlink was added while overlay is mounted. Adding a lower
                 * hardlink and then unlinking all overlay hardlinks would drop
                 * overlay nlink to zero before all upper inodes are unlinked.
                 * As a safety measure, when that situation is detected, set
                 * the overlay nlink to the index inode nlink minus one for the
                 * index entry itself.
                 */
                set_nlink(d_inode(dentry), inode->i_nlink - 1);
                ovl_set_nlink_upper(dentry);
                goto out;
        }

        inode_lock_nested(dir, I_MUTEX_PARENT);
        index = lookup_one_len(name.name, indexdir, name.len);
        err = PTR_ERR(index);
        if (IS_ERR(index)) {
                index = NULL;
        } else if (ovl_index_all(dentry->d_sb)) {
                /* Whiteout orphan index to block future open by handle */
                err = ovl_cleanup_and_whiteout(OVL_FS(dentry->d_sb),
                                               dir, index);
        } else {
                /* Cleanup orphan index entries */
                err = ovl_cleanup(dir, index);
        }

        inode_unlock(dir);
        if (err)
                goto fail;

out:
        kfree(name.name);
        dput(index);
        return;

fail:
        pr_err("cleanup index of '%pd2' failed (%i)\n", dentry, err);
        goto out;
}

/*
 * Operations that change overlay inode and upper inode nlink need to be
 * synchronized with copy up for persistent nlink accounting.
 */
int ovl_nlink_start(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        const struct cred *old_cred;
        int err;

        if (WARN_ON(!inode))
                return -ENOENT;

        /*
         * With inodes index is enabled, we store the union overlay nlink
         * in an xattr on the index inode. When whiting out an indexed lower,
         * we need to decrement the overlay persistent nlink, but before the
         * first copy up, we have no upper index inode to store the xattr.
         *
         * As a workaround, before whiteout/rename over an indexed lower,
         * copy up to create the upper index. Creating the upper index will
         * initialize the overlay nlink, so it could be dropped if unlink
         * or rename succeeds.
         *
         * TODO: implement metadata only index copy up when called with
         *       ovl_copy_up_flags(dentry, O_PATH).
         */
        if (ovl_need_index(dentry) && !ovl_dentry_has_upper_alias(dentry)) {
                err = ovl_copy_up(dentry);
                if (err)
                        return err;
        }

        err = ovl_inode_lock_interruptible(inode);
        if (err)
                return err;

        if (d_is_dir(dentry) || !ovl_test_flag(OVL_INDEX, inode))
                goto out;

        old_cred = ovl_override_creds(dentry->d_sb);
        /*
         * The overlay inode nlink should be incremented/decremented IFF the
         * upper operation succeeds, along with nlink change of upper inode.
         * Therefore, before link/unlink/rename, we store the union nlink
         * value relative to the upper inode nlink in an upper inode xattr.
         */
        err = ovl_set_nlink_upper(dentry);
        revert_creds(old_cred);

out:
        if (err)
                ovl_inode_unlock(inode);

        return err;
}

void ovl_nlink_end(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        if (ovl_test_flag(OVL_INDEX, inode) && inode->i_nlink == 0) {
                const struct cred *old_cred;

                old_cred = ovl_override_creds(dentry->d_sb);
                ovl_cleanup_index(dentry);
                revert_creds(old_cred);
        }

        ovl_inode_unlock(inode);
}

int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir)
{
        /* Workdir should not be the same as upperdir */
        if (workdir == upperdir)
                goto err;

        /* Workdir should not be subdir of upperdir and vice versa */
        if (lock_rename(workdir, upperdir) != NULL)
                goto err_unlock;

        return 0;

err_unlock:
        unlock_rename(workdir, upperdir);
err:
        pr_err("failed to lock workdir+upperdir\n");
        return -EIO;
}

/* err < 0, 0 if no metacopy xattr, 1 if metacopy xattr found */
int ovl_check_metacopy_xattr(struct ovl_fs *ofs, struct dentry *dentry)
{
        int res;

        /* Only regular files can have metacopy xattr */
        if (!S_ISREG(d_inode(dentry)->i_mode))
                return 0;

        res = ovl_do_getxattr(ofs, dentry, OVL_XATTR_METACOPY, NULL, 0);
        if (res < 0) {
                if (res == -ENODATA || res == -EOPNOTSUPP)
                        return 0;
                /*
                 * getxattr on user.* may fail with EACCES in case there's no
                 * read permission on the inode.  Not much we can do, other than
                 * tell the caller that this is not a metacopy inode.
                 */
                if (ofs->config.userxattr && res == -EACCES)
                        return 0;
                goto out;
        }

        return 1;
out:
        pr_warn_ratelimited("failed to get metacopy (%i)\n", res);
        return res;
}

bool ovl_is_metacopy_dentry(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;

        if (!d_is_reg(dentry))
                return false;

        if (ovl_dentry_upper(dentry)) {
                if (!ovl_has_upperdata(d_inode(dentry)))
                        return true;
                return false;
        }

        return (oe->numlower > 1);
}

char *ovl_get_redirect_xattr(struct ovl_fs *ofs, struct dentry *dentry,
                             int padding)
{
        int res;
        char *s, *next, *buf = NULL;

        res = ovl_do_getxattr(ofs, dentry, OVL_XATTR_REDIRECT, NULL, 0);
        if (res == -ENODATA || res == -EOPNOTSUPP)
                return NULL;
        if (res < 0)
                goto fail;
        if (res == 0)
                goto invalid;

        buf = kzalloc(res + padding + 1, GFP_KERNEL);
        if (!buf)
                return ERR_PTR(-ENOMEM);

        res = ovl_do_getxattr(ofs, dentry, OVL_XATTR_REDIRECT, buf, res);
        if (res < 0)
                goto fail;
        if (res == 0)
                goto invalid;

        if (buf[0] == '/') {
                for (s = buf; *s++ == '/'; s = next) {
                        next = strchrnul(s, '/');
                        if (s == next)
                                goto invalid;
                }
        } else {
                if (strchr(buf, '/') != NULL)
                        goto invalid;
        }

        return buf;
invalid:
        pr_warn_ratelimited("invalid redirect (%s)\n", buf);
        res = -EINVAL;
        goto err_free;
fail:
        pr_warn_ratelimited("failed to get redirect (%i)\n", res);
err_free:
        kfree(buf);
        return ERR_PTR(res);
}