// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2017-2018 HUAWEI, Inc.
 *             https://www.huawei.com/
 * Copyright (C) 2022, Alibaba Cloud
 */
#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 erofs_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 = mid >= ndirents - 1 ?
                                data + dirblksize :
                                data + nameoff_from_disk(de[mid + 1].nameoff,
                                                         dirblksize)
                };

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

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

        return ERR_PTR(-ENOENT);
}

static void *erofs_find_target_block(struct erofs_buf *target,
                struct inode *dir, struct erofs_qstr *name, int *_ndirents)
{
        unsigned int bsz = i_blocksize(dir);
        int head = 0, back = erofs_iblks(dir) - 1;
        unsigned int startprfx = 0, endprfx = 0;
        void *candidate = ERR_PTR(-ENOENT);

        while (head <= back) {
                const int mid = head + (back - head) / 2;
                struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
                struct erofs_dirent *de;

                buf.mapping = dir->i_mapping;
                de = erofs_bread(&buf, erofs_pos(dir->i_sb, mid), true);
                if (!IS_ERR(de)) {
                        const int nameoff = nameoff_from_disk(de->nameoff, bsz);
                        const int ndirents = nameoff / sizeof(*de);
                        int diff;
                        unsigned int matched;
                        struct erofs_qstr dname;

                        if (!ndirents) {
                                erofs_put_metabuf(&buf);
                                erofs_err(dir->i_sb,
                                          "corrupted dir block %d @ nid %llu",
                                          mid, EROFS_I(dir)->nid);
                                DBG_BUGON(1);
                                de = ERR_PTR(-EFSCORRUPTED);
                                goto out;
                        }

                        matched = min(startprfx, endprfx);

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

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

                        if (diff < 0) {
                                erofs_put_metabuf(&buf);
                                back = mid - 1;
                                endprfx = matched;
                                continue;
                        }

                        if (!IS_ERR(candidate))
                                erofs_put_metabuf(target);
                        *target = buf;
                        if (!diff) {
                                *_ndirents = 0;
                                return de;
                        }
                        head = mid + 1;
                        startprfx = matched;
                        candidate = de;
                        *_ndirents = ndirents;
                        continue;
                }
out:            /* free if the candidate is valid */
                if (!IS_ERR(candidate))
                        erofs_put_metabuf(target);
                return de;
        }
        return candidate;
}

int erofs_namei(struct inode *dir, const struct qstr *name, erofs_nid_t *nid,
                unsigned int *d_type)
{
        int ndirents;
        struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
        struct erofs_dirent *de;
        struct erofs_qstr qn;

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

        qn.name = name->name;
        qn.end = name->name + name->len;
        buf.mapping = dir->i_mapping;

        ndirents = 0;
        de = erofs_find_target_block(&buf, dir, &qn, &ndirents);
        if (IS_ERR(de))
                return PTR_ERR(de);

        if (ndirents)
                de = find_target_dirent(&qn, (u8 *)de, i_blocksize(dir),
                                        ndirents);

        if (!IS_ERR(de)) {
                *nid = le64_to_cpu(de->nid);
                *d_type = de->file_type;
        }
        erofs_put_metabuf(&buf);
        return PTR_ERR_OR_ZERO(de);
}

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;

        trace_erofs_lookup(dir, dentry, flags);

        if (dentry->d_name.len > EROFS_NAME_LEN)
                return ERR_PTR(-ENAMETOOLONG);

        err = erofs_namei(dir, &dentry->d_name, &nid, &d_type);

        if (err == -ENOENT)
                /* negative dentry */
                inode = NULL;
        else if (err)
                inode = ERR_PTR(err);
        else
                inode = erofs_iget(dir->i_sb, nid);
        return d_splice_alias(inode, dentry);
}

const struct inode_operations erofs_dir_iops = {
        .lookup = erofs_lookup,
        .getattr = erofs_getattr,
        .listxattr = erofs_listxattr,
        .get_inode_acl = erofs_get_acl,
        .fiemap = erofs_fiemap,
};