fs/erofs/namei.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2017-2018 HUAWEI, Inc.
   4  *             http://www.huawei.com/
   5  * Created by Gao Xiang <gaoxiang25@huawei.com>
   6  */
   7 #include "xattr.h"
   8
   9 #include <trace/events/erofs.h>
  10
  11 struct erofs_qstr {
  12         const unsigned char *name;
  13         const unsigned char *end;
  14 };
  15
  16 /* based on the end of qn is accurate and it must have the trailing '\0' */
  17 static inline int dirnamecmp(const struct erofs_qstr *qn,
  18                              const struct erofs_qstr *qd,
  19                              unsigned int *matched)
  20 {
  21         unsigned int i = *matched;
  22
  23         /*
  24          * on-disk error, let's only BUG_ON in the debugging mode.
  25          * otherwise, it will return 1 to just skip the invalid name
  26          * and go on (in consideration of the lookup performance).
  27          */
  28         DBG_BUGON(qd->name > qd->end);
  29
  30         /* qd could not have trailing '\0' */
  31         /* However it is absolutely safe if < qd->end */
  32         while (qd->name + i < qd->end && qd->name[i] != '\0') {
  33                 if (qn->name[i] != qd->name[i]) {
  34                         *matched = i;
  35                         return qn->name[i] > qd->name[i] ? 1 : -1;
  36                 }
  37                 ++i;
  38         }
  39         *matched = i;
  40         /* See comments in __d_alloc on the terminating NUL character */
  41         return qn->name[i] == '\0' ? 0 : 1;
  42 }
  43
  44 #define nameoff_from_disk(off, sz)      (le16_to_cpu(off) & ((sz) - 1))
  45
  46 static struct erofs_dirent *find_target_dirent(struct erofs_qstr *name,
  47                                                u8 *data,
  48                                                unsigned int dirblksize,
  49                                                const int ndirents)
  50 {
  51         int head, back;
  52         unsigned int startprfx, endprfx;
  53         struct erofs_dirent *const de = (struct erofs_dirent *)data;
  54
  55         /* since the 1st dirent has been evaluated previously */
  56         head = 1;
  57         back = ndirents - 1;
  58         startprfx = endprfx = 0;
  59
  60         while (head <= back) {
  61                 const int mid = head + (back - head) / 2;
  62                 const int nameoff = nameoff_from_disk(de[mid].nameoff,
  63                                                       dirblksize);
  64                 unsigned int matched = min(startprfx, endprfx);
  65                 struct erofs_qstr dname = {
  66                         .name = data + nameoff,
  67                         .end = unlikely(mid >= ndirents - 1) ?
  68                                 data + dirblksize :
  69                                 data + nameoff_from_disk(de[mid + 1].nameoff,
  70                                                          dirblksize)
  71                 };
  72
  73                 /* string comparison without already matched prefix */
  74                 int ret = dirnamecmp(name, &dname, &matched);
  75
  76                 if (unlikely(!ret)) {
  77                         return de + mid;
  78                 } else if (ret > 0) {
  79                         head = mid + 1;
  80                         startprfx = matched;
  81                 } else {
  82                         back = mid - 1;
  83                         endprfx = matched;
  84                 }
  85         }
  86
  87         return ERR_PTR(-ENOENT);
  88 }
  89
  90 static struct page *find_target_block_classic(struct inode *dir,
  91                                               struct erofs_qstr *name,
  92                                               int *_ndirents)
  93 {
  94         unsigned int startprfx, endprfx;
  95         int head, back;
  96         struct address_space *const mapping = dir->i_mapping;
  97         struct page *candidate = ERR_PTR(-ENOENT);
  98
  99         startprfx = endprfx = 0;
 100         head = 0;
 101         back = inode_datablocks(dir) - 1;
 102
 103         while (head <= back) {
 104                 const int mid = head + (back - head) / 2;
 105                 struct page *page = read_mapping_page(mapping, mid, NULL);
 106
 107                 if (!IS_ERR(page)) {
 108                         struct erofs_dirent *de = kmap_atomic(page);
 109                         const int nameoff = nameoff_from_disk(de->nameoff,
 110                                                               EROFS_BLKSIZ);
 111                         const int ndirents = nameoff / sizeof(*de);
 112                         int diff;
 113                         unsigned int matched;
 114                         struct erofs_qstr dname;
 115
 116                         if (unlikely(!ndirents)) {
 117                                 kunmap_atomic(de);
 118                                 put_page(page);
 119                                 errln("corrupted dir block %d @ nid %llu",
 120                                       mid, EROFS_V(dir)->nid);
 121                                 DBG_BUGON(1);
 122                                 page = ERR_PTR(-EFSCORRUPTED);
 123                                 goto out;
 124                         }
 125
 126                         matched = min(startprfx, endprfx);
 127
 128                         dname.name = (u8 *)de + nameoff;
 129                         if (ndirents == 1)
 130                                 dname.end = (u8 *)de + EROFS_BLKSIZ;
 131                         else
 132                                 dname.end = (u8 *)de +
 133                                         nameoff_from_disk(de[1].nameoff,
 134                                                           EROFS_BLKSIZ);
 135
 136                         /* string comparison without already matched prefix */
 137                         diff = dirnamecmp(name, &dname, &matched);
 138                         kunmap_atomic(de);
 139
 140                         if (unlikely(!diff)) {
 141                                 *_ndirents = 0;
 142                                 goto out;
 143                         } else if (diff > 0) {
 144                                 head = mid + 1;
 145                                 startprfx = matched;
 146
 147                                 if (!IS_ERR(candidate))
 148                                         put_page(candidate);
 149                                 candidate = page;
 150                                 *_ndirents = ndirents;
 151                         } else {
 152                                 put_page(page);
 153
 154                                 back = mid - 1;
 155                                 endprfx = matched;
 156                         }
 157                         continue;
 158                 }
 159 out:            /* free if the candidate is valid */
 160                 if (!IS_ERR(candidate))
 161                         put_page(candidate);
 162                 return page;
 163         }
 164         return candidate;
 165 }
 166
 167 int erofs_namei(struct inode *dir,
 168                 struct qstr *name,
 169                 erofs_nid_t *nid, unsigned int *d_type)
 170 {
 171         int ndirents;
 172         struct page *page;
 173         void *data;
 174         struct erofs_dirent *de;
 175         struct erofs_qstr qn;
 176
 177         if (unlikely(!dir->i_size))
 178                 return -ENOENT;
 179
 180         qn.name = name->name;
 181         qn.end = name->name + name->len;
 182
 183         ndirents = 0;
 184         page = find_target_block_classic(dir, &qn, &ndirents);
 185
 186         if (IS_ERR(page))
 187                 return PTR_ERR(page);
 188
 189         data = kmap_atomic(page);
 190         /* the target page has been mapped */
 191         if (ndirents)
 192                 de = find_target_dirent(&qn, data, EROFS_BLKSIZ, ndirents);
 193         else
 194                 de = (struct erofs_dirent *)data;
 195
 196         if (!IS_ERR(de)) {
 197                 *nid = le64_to_cpu(de->nid);
 198                 *d_type = de->file_type;
 199         }
 200
 201         kunmap_atomic(data);
 202         put_page(page);
 203
 204         return PTR_ERR_OR_ZERO(de);
 205 }
 206
 207 /* NOTE: i_mutex is already held by vfs */
 208 static struct dentry *erofs_lookup(struct inode *dir,
 209                                    struct dentry *dentry,
 210                                    unsigned int flags)
 211 {
 212         int err;
 213         erofs_nid_t nid;
 214         unsigned int d_type;
 215         struct inode *inode;
 216
 217         DBG_BUGON(!d_really_is_negative(dentry));
 218         /* dentry must be unhashed in lookup, no need to worry about */
 219         DBG_BUGON(!d_unhashed(dentry));
 220
 221         trace_erofs_lookup(dir, dentry, flags);
 222
 223         /* file name exceeds fs limit */
 224         if (unlikely(dentry->d_name.len > EROFS_NAME_LEN))
 225                 return ERR_PTR(-ENAMETOOLONG);
 226
 227         /* false uninitialized warnings on gcc 4.8.x */
 228         err = erofs_namei(dir, &dentry->d_name, &nid, &d_type);
 229
 230         if (err == -ENOENT) {
 231                 /* negative dentry */
 232                 inode = NULL;
 233         } else if (unlikely(err)) {
 234                 inode = ERR_PTR(err);
 235         } else {
 236                 debugln("%s, %s (nid %llu) found, d_type %u", __func__,
 237                         dentry->d_name.name, nid, d_type);
 238                 inode = erofs_iget(dir->i_sb, nid, d_type == FT_DIR);
 239         }
 240         return d_splice_alias(inode, dentry);
 241 }
 242
 243 const struct inode_operations erofs_dir_iops = {
 244         .lookup = erofs_lookup,
 245         .getattr = erofs_getattr,
 246 #ifdef CONFIG_EROFS_FS_XATTR
 247         .listxattr = erofs_listxattr,
 248 #endif
 249         .get_acl = erofs_get_acl,
 250 };
 251