// SPDX-License-Identifier: GPL-2.0
/*
 * linux/drivers/staging/erofs/namei.c
 *
 * Copyright (C) 2017-2018 HUAWEI, Inc.
 *             http://www.huawei.com/
 * Created by Gao Xiang <gaoxiang25@huawei.com>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of the Linux
 * distribution for more details.
 */
#include "internal.h"
#include "xattr.h"

#include <trace/events/erofs.h>

struct erofs_qstr {
        const unsigned char *name;
        const unsigned char *end;
};

/* based on the end of qn is accurate and it must have the trailing '\0' */
static inline int dirnamecmp(const struct erofs_qstr *qn,
                             const struct erofs_qstr *qd,
                             unsigned int *matched)
{
        unsigned int i = *matched;

        /*
         * on-disk error, let's only BUG_ON in the debugging mode.
         * otherwise, it will return 1 to just skip the invalid name
         * and go on (in consideration of the lookup performance).
         */
        DBG_BUGON(qd->name > qd->end);

        /* qd could not have trailing '\0' */
        /* However it is absolutely safe if < qd->end */
        while (qd->name + i < qd->end && qd->name[i] != '\0') {
                if (qn->name[i] != qd->name[i]) {
                        *matched = i;
                        return qn->name[i] > qd->name[i] ? 1 : -1;
                }
                ++i;
        }
        *matched = i;
        /* See comments in __d_alloc on the terminating NUL character */
        return qn->name[i] == '\0' ? 0 : 1;
}

#define nameoff_from_disk(off, sz)      (le16_to_cpu(off) & ((sz) - 1))

static struct erofs_dirent *find_target_dirent(struct erofs_qstr *name,
                                               u8 *data,
                                               unsigned int dirblksize,
                                               const int ndirents)
{
        int head, back;
        unsigned int startprfx, endprfx;
        struct erofs_dirent *const de = (struct erofs_dirent *)data;

        /* since the 1st dirent has been evaluated previously */
        head = 1;
        back = ndirents - 1;
        startprfx = endprfx = 0;

        while (head <= back) {
                const int mid = head + (back - head) / 2;
                const int nameoff = nameoff_from_disk(de[mid].nameoff,
                                                      dirblksize);
                unsigned int matched = min(startprfx, endprfx);
                struct erofs_qstr dname = {
                        .name = data + nameoff,
                        .end = unlikely(mid >= ndirents - 1) ?
                                data + dirblksize :
                                data + nameoff_from_disk(de[mid + 1].nameoff,
                                                         dirblksize)
                };

                /* string comparison without already matched prefix */
                int ret = dirnamecmp(name, &dname, &matched);

                if (unlikely(!ret)) {
                        return de + mid;
                } else if (ret > 0) {
                        head = mid + 1;
                        startprfx = matched;
                } else {
                        back = mid - 1;
                        endprfx = matched;
                }
        }

        return ERR_PTR(-ENOENT);
}

static struct page *find_target_block_classic(struct inode *dir,
                                              struct erofs_qstr *name,
                                              int *_ndirents)
{
        unsigned int startprfx, endprfx;
        int head, back;
        struct address_space *const mapping = dir->i_mapping;
        struct page *candidate = ERR_PTR(-ENOENT);

        startprfx = endprfx = 0;
        head = 0;
        back = inode_datablocks(dir) - 1;

        while (head <= back) {
                const int mid = head + (back - head) / 2;
                struct page *page = read_mapping_page(mapping, mid, NULL);

                if (!IS_ERR(page)) {
                        struct erofs_dirent *de = kmap_atomic(page);
                        const int nameoff = nameoff_from_disk(de->nameoff,
                                                              EROFS_BLKSIZ);
                        const int ndirents = nameoff / sizeof(*de);
                        int diff;
                        unsigned int matched;
                        struct erofs_qstr dname;

                        if (unlikely(!ndirents)) {
                                DBG_BUGON(1);
                                kunmap_atomic(de);
                                put_page(page);
                                page = ERR_PTR(-EIO);
                                goto out;
                        }

                        matched = min(startprfx, endprfx);

                        dname.name = (u8 *)de + nameoff;
                        if (ndirents == 1)
                                dname.end = (u8 *)de + EROFS_BLKSIZ;
                        else
                                dname.end = (u8 *)de +
                                        nameoff_from_disk(de[1].nameoff,
                                                          EROFS_BLKSIZ);

                        /* string comparison without already matched prefix */
                        diff = dirnamecmp(name, &dname, &matched);
                        kunmap_atomic(de);

                        if (unlikely(!diff)) {
                                *_ndirents = 0;
                                goto out;
                        } else if (diff > 0) {
                                head = mid + 1;
                                startprfx = matched;

                                if (!IS_ERR(candidate))
                                        put_page(candidate);
                                candidate = page;
                                *_ndirents = ndirents;
                        } else {
                                put_page(page);

                                back = mid - 1;
                                endprfx = matched;
                        }
                        continue;
                }
out:            /* free if the candidate is valid */
                if (!IS_ERR(candidate))
                        put_page(candidate);
                return page;
        }
        return candidate;
}

int erofs_namei(struct inode *dir,
                struct qstr *name,
                erofs_nid_t *nid, unsigned int *d_type)
{
        int ndirents;
        struct page *page;
        void *data;
        struct erofs_dirent *de;
        struct erofs_qstr qn;

        if (unlikely(!dir->i_size))
                return -ENOENT;

        qn.name = name->name;
        qn.end = name->name + name->len;

        ndirents = 0;
        page = find_target_block_classic(dir, &qn, &ndirents);

        if (IS_ERR(page))
                return PTR_ERR(page);

        data = kmap_atomic(page);
        /* the target page has been mapped */
        if (ndirents)
                de = find_target_dirent(&qn, data, EROFS_BLKSIZ, ndirents);
        else
                de = (struct erofs_dirent *)data;

        if (!IS_ERR(de)) {
                *nid = le64_to_cpu(de->nid);
                *d_type = de->file_type;
        }

        kunmap_atomic(data);
        put_page(page);

        return PTR_ERR_OR_ZERO(de);
}

/* NOTE: i_mutex is already held by vfs */
static struct dentry *erofs_lookup(struct inode *dir,
                                   struct dentry *dentry,
                                   unsigned int flags)
{
        int err;
        erofs_nid_t nid;
        unsigned int d_type;
        struct inode *inode;

        DBG_BUGON(!d_really_is_negative(dentry));
        /* dentry must be unhashed in lookup, no need to worry about */
        DBG_BUGON(!d_unhashed(dentry));

        trace_erofs_lookup(dir, dentry, flags);

        /* file name exceeds fs limit */
        if (unlikely(dentry->d_name.len > EROFS_NAME_LEN))
                return ERR_PTR(-ENAMETOOLONG);

        /* false uninitialized warnings on gcc 4.8.x */
        err = erofs_namei(dir, &dentry->d_name, &nid, &d_type);

        if (err == -ENOENT) {
                /* negative dentry */
                inode = NULL;
        } else if (unlikely(err)) {
                inode = ERR_PTR(err);
        } else {
                debugln("%s, %s (nid %llu) found, d_type %u", __func__,
                        dentry->d_name.name, nid, d_type);
                inode = erofs_iget(dir->i_sb, nid, d_type == EROFS_FT_DIR);
        }
        return d_splice_alias(inode, dentry);
}

const struct inode_operations erofs_dir_iops = {
        .lookup = erofs_lookup,
#ifdef CONFIG_EROFS_FS_XATTR
        .listxattr = erofs_listxattr,
#endif
        .get_acl = erofs_get_acl,
};