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Subject[PATCH v2 08/24] erofs: add namei functions
Date
This commit adds functions that transfer names to inodes.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
fs/erofs/namei.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 246 insertions(+)
create mode 100644 fs/erofs/namei.c

diff --git a/fs/erofs/namei.c b/fs/erofs/namei.c
new file mode 100644
index 000000000000..7665d3603503
--- /dev/null
+++ b/fs/erofs/namei.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/erofs/namei.c
+ *
+ * Copyright (C) 2017-2018 HUAWEI, Inc.
+ * http://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ */
+#include "internal.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,
+ .getattr = erofs_getattr,
+};
+
--
2.17.1
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