staging: erofs: add namei functions

This commit adds functions that transfer names to inodes.
Signed-off-by: Miao Xie <miaoxie@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/namei.c

+// 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"
+
+/* based on the value of qn->len is accurate */
+static inline int dirnamecmp(struct qstr *qn,
+	struct qstr *qd, unsigned *matched)
+{
+	unsigned i = *matched, len = min(qn->len, qd->len);
+loop:
+	if (unlikely(i >= len)) {
+		*matched = i;
+		if (qn->len < qd->len) {
+			/*
+			 * actually (qn->len == qd->len)
+			 * when qd->name[i] == '\0'
+			 */
+			return qd->name[i] == '\0' ? 0 : -1;
+		}
+		return (qn->len > qd->len);
+	}
+
+	if (qn->name[i] != qd->name[i]) {
+		*matched = i;
+		return qn->name[i] > qd->name[i] ? 1 : -1;
+	}
+
+	++i;
+	goto loop;
+}
+
+static struct erofs_dirent *find_target_dirent(
+	struct qstr *name,
+	u8 *data, int maxsize)
+{
+	unsigned ndirents, head, back;
+	unsigned startprfx, endprfx;
+	struct erofs_dirent *const de = (struct erofs_dirent *)data;
+
+	/* make sure that maxsize is valid */
+	BUG_ON(maxsize < sizeof(struct erofs_dirent));
+
+	ndirents = le16_to_cpu(de->nameoff) / sizeof(*de);
+
+	/* corrupted dir (may be unnecessary...) */
+	BUG_ON(!ndirents);
+
+	head = 0;
+	back = ndirents - 1;
+	startprfx = endprfx = 0;
+
+	while (head <= back) {
+		unsigned mid = head + (back - head) / 2;
+		unsigned nameoff = le16_to_cpu(de[mid].nameoff);
+		unsigned matched = min(startprfx, endprfx);
+
+		struct qstr dname = QSTR_INIT(data + nameoff,
+			unlikely(mid >= ndirents - 1) ?
+				maxsize - nameoff :
+				le16_to_cpu(de[mid + 1].nameoff) - nameoff);
+
+		/* 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 if (unlikely(mid < 1))	/* fix "mid" overflow */
+			break;
+		else {
+			back = mid - 1;
+			endprfx = matched;
+		}
+	}
+
+	return ERR_PTR(-ENOENT);
+}
+
+static struct page *find_target_block_classic(
+	struct inode *dir,
+	struct qstr *name, int *_diff)
+{
+	unsigned startprfx, endprfx;
+	unsigned 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) {
+		unsigned mid = head + (back - head) / 2;
+		struct page *page = read_mapping_page(mapping, mid, NULL);
+
+		if (IS_ERR(page)) {
+exact_out:
+			if (!IS_ERR(candidate)) /* valid candidate */
+				put_page(candidate);
+			return page;
+		} else {
+			int diff;
+			unsigned ndirents, matched;
+			struct qstr dname;
+			struct erofs_dirent *de = kmap_atomic(page);
+			unsigned nameoff = le16_to_cpu(de->nameoff);
+
+			ndirents = nameoff / sizeof(*de);
+
+			/* corrupted dir (should have one entry at least) */
+			BUG_ON(!ndirents || nameoff > PAGE_SIZE);
+
+			matched = min(startprfx, endprfx);
+
+			dname.name = (u8 *)de + nameoff;
+			dname.len = ndirents == 1 ?
+				/* since the rest of the last page is 0 */
+				EROFS_BLKSIZ - nameoff
+				: le16_to_cpu(de[1].nameoff) - nameoff;
+
+			/* string comparison without already matched prefix */
+			diff = dirnamecmp(name, &dname, &matched);
+			kunmap_atomic(de);
+
+			if (unlikely(!diff)) {
+				*_diff = 0;
+				goto exact_out;
+			} else if (diff > 0) {
+				head = mid + 1;
+				startprfx = matched;
+
+				if (likely(!IS_ERR(candidate)))
+					put_page(candidate);
+				candidate = page;
+			} else {
+				put_page(page);
+
+				if (unlikely(mid < 1))	/* fix "mid" overflow */
+					break;
+
+				back = mid - 1;
+				endprfx = matched;
+			}
+		}
+	}
+	*_diff = 1;
+	return candidate;
+}
+
+int erofs_namei(struct inode *dir,
+	struct qstr *name,
+	erofs_nid_t *nid, unsigned *d_type)
+{
+	int diff;
+	struct page *page;
+	u8 *data;
+	struct erofs_dirent *de;
+
+	if (unlikely(!dir->i_size))
+		return -ENOENT;
+
+	diff = 1;
+	page = find_target_block_classic(dir, name, &diff);
+
+	if (unlikely(IS_ERR(page)))
+		return PTR_ERR(page);
+
+	data = kmap_atomic(page);
+	/* the target page has been mapped */
+	de = likely(diff) ?
+		/* since the rest of the last page is 0 */
+		find_target_dirent(name, data, EROFS_BLKSIZ) :
+		(struct erofs_dirent *)data;
+
+	if (likely(!IS_ERR(de))) {
+		*nid = le64_to_cpu(de->nid);
+		*d_type = de->file_type;
+	}
+
+	kunmap_atomic(data);
+	put_page(page);
+
+	return IS_ERR(de) ? PTR_ERR(de) : 0;
+}
+
+/* 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 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));
+
+	/* 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;
+		goto negative_out;
+	} else if (unlikely(err))
+		return ERR_PTR(err);
+
+	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);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+negative_out:
+	return d_splice_alias(inode, dentry);
+}
+
+const struct inode_operations erofs_dir_iops = {
+	.lookup = erofs_lookup,
+};
+
+const struct inode_operations erofs_dir_xattr_iops = {
+	.lookup = erofs_lookup,
+};
+