symlinks.c

   1 #include "cache.h"
   2
   3 /*
   4  * Returns the length (on a path component basis) of the longest
   5  * common prefix match of 'name_a' and 'name_b'.
   6  */
   7 static int longest_path_match(const char *name_a, int len_a,
   8                               const char *name_b, int len_b,
   9                               int *previous_slash)
  10 {
  11         int max_len, match_len = 0, match_len_prev = 0, i = 0;
  12
  13         max_len = len_a < len_b ? len_a : len_b;
  14         while (i < max_len && name_a[i] == name_b[i]) {
  15                 if (name_a[i] == '/') {
  16                         match_len_prev = match_len;
  17                         match_len = i;
  18                 }
  19                 i++;
  20         }
  21         /*
  22          * Is 'name_b' a substring of 'name_a', the other way around,
  23          * or is 'name_a' and 'name_b' the exact same string?
  24          */
  25         if (i >= max_len && ((len_a > len_b && name_a[len_b] == '/') ||
  26                              (len_a < len_b && name_b[len_a] == '/') ||
  27                              (len_a == len_b))) {
  28                 match_len_prev = match_len;
  29                 match_len = i;
  30         }
  31         *previous_slash = match_len_prev;
  32         return match_len;
  33 }
  34
  35 static struct cache_def default_cache;
  36
  37 static inline void reset_lstat_cache(struct cache_def *cache)
  38 {
  39         cache->path[0] = '\0';
  40         cache->len = 0;
  41         cache->flags = 0;
  42         /*
  43          * The track_flags and prefix_len_stat_func members is only
  44          * set by the safeguard rule inside lstat_cache()
  45          */
  46 }
  47
  48 #define FL_DIR      (1 << 0)
  49 #define FL_NOENT    (1 << 1)
  50 #define FL_SYMLINK  (1 << 2)
  51 #define FL_LSTATERR (1 << 3)
  52 #define FL_ERR      (1 << 4)
  53 #define FL_FULLPATH (1 << 5)
  54
  55 /*
  56  * Check if name 'name' of length 'len' has a symlink leading
  57  * component, or if the directory exists and is real, or not.
  58  *
  59  * To speed up the check, some information is allowed to be cached.
  60  * This can be indicated by the 'track_flags' argument, which also can
  61  * be used to indicate that we should check the full path.
  62  *
  63  * The 'prefix_len_stat_func' parameter can be used to set the length
  64  * of the prefix, where the cache should use the stat() function
  65  * instead of the lstat() function to test each path component.
  66  */
  67 static int lstat_cache_matchlen(struct cache_def *cache,
  68                                 const char *name, int len,
  69                                 int *ret_flags, int track_flags,
  70                                 int prefix_len_stat_func)
  71 {
  72         int match_len, last_slash, last_slash_dir, previous_slash;
  73         int save_flags, max_len, ret;
  74         struct stat st;
  75
  76         if (cache->track_flags != track_flags ||
  77             cache->prefix_len_stat_func != prefix_len_stat_func) {
  78                 /*
  79                  * As a safeguard rule we clear the cache if the
  80                  * values of track_flags and/or prefix_len_stat_func
  81                  * does not match with the last supplied values.
  82                  */
  83                 reset_lstat_cache(cache);
  84                 cache->track_flags = track_flags;
  85                 cache->prefix_len_stat_func = prefix_len_stat_func;
  86                 match_len = last_slash = 0;
  87         } else {
  88                 /*
  89                  * Check to see if we have a match from the cache for
  90                  * the 2 "excluding" path types.
  91                  */
  92                 match_len = last_slash =
  93                         longest_path_match(name, len, cache->path, cache->len,
  94                                            &previous_slash);
  95                 *ret_flags = cache->flags & track_flags & (FL_NOENT|FL_SYMLINK);
  96
  97                 if (!(track_flags & FL_FULLPATH) && match_len == len)
  98                         match_len = last_slash = previous_slash;
  99
 100                 if (*ret_flags && match_len == cache->len)
 101                         return match_len;
 102                 /*
 103                  * If we now have match_len > 0, we would know that
 104                  * the matched part will always be a directory.
 105                  *
 106                  * Also, if we are tracking directories and 'name' is
 107                  * a substring of the cache on a path component basis,
 108                  * we can return immediately.
 109                  */
 110                 *ret_flags = track_flags & FL_DIR;
 111                 if (*ret_flags && len == match_len)
 112                         return match_len;
 113         }
 114
 115         /*
 116          * Okay, no match from the cache so far, so now we have to
 117          * check the rest of the path components.
 118          */
 119         *ret_flags = FL_DIR;
 120         last_slash_dir = last_slash;
 121         max_len = len < PATH_MAX ? len : PATH_MAX;
 122         while (match_len < max_len) {
 123                 do {
 124                         cache->path[match_len] = name[match_len];
 125                         match_len++;
 126                 } while (match_len < max_len && name[match_len] != '/');
 127                 if (match_len >= max_len && !(track_flags & FL_FULLPATH))
 128                         break;
 129                 last_slash = match_len;
 130                 cache->path[last_slash] = '\0';
 131
 132                 if (last_slash <= prefix_len_stat_func)
 133                         ret = stat(cache->path, &st);
 134                 else
 135                         ret = lstat(cache->path, &st);
 136
 137                 if (ret) {
 138                         *ret_flags = FL_LSTATERR;
 139                         if (errno == ENOENT)
 140                                 *ret_flags |= FL_NOENT;
 141                 } else if (S_ISDIR(st.st_mode)) {
 142                         last_slash_dir = last_slash;
 143                         continue;
 144                 } else if (S_ISLNK(st.st_mode)) {
 145                         *ret_flags = FL_SYMLINK;
 146                 } else {
 147                         *ret_flags = FL_ERR;
 148                 }
 149                 break;
 150         }
 151
 152         /*
 153          * At the end update the cache.  Note that max 3 different
 154          * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached
 155          * for the moment!
 156          */
 157         save_flags = *ret_flags & track_flags & (FL_NOENT|FL_SYMLINK);
 158         if (save_flags && last_slash > 0 && last_slash <= PATH_MAX) {
 159                 cache->path[last_slash] = '\0';
 160                 cache->len = last_slash;
 161                 cache->flags = save_flags;
 162         } else if ((track_flags & FL_DIR) &&
 163                    last_slash_dir > 0 && last_slash_dir <= PATH_MAX) {
 164                 /*
 165                  * We have a separate test for the directory case,
 166                  * since it could be that we have found a symlink or a
 167                  * non-existing directory and the track_flags says
 168                  * that we cannot cache this fact, so the cache would
 169                  * then have been left empty in this case.
 170                  *
 171                  * But if we are allowed to track real directories, we
 172                  * can still cache the path components before the last
 173                  * one (the found symlink or non-existing component).
 174                  */
 175                 cache->path[last_slash_dir] = '\0';
 176                 cache->len = last_slash_dir;
 177                 cache->flags = FL_DIR;
 178         } else {
 179                 reset_lstat_cache(cache);
 180         }
 181         return match_len;
 182 }
 183
 184 static int lstat_cache(struct cache_def *cache, const char *name, int len,
 185                        int track_flags, int prefix_len_stat_func)
 186 {
 187         int flags;
 188         (void)lstat_cache_matchlen(cache, name, len, &flags, track_flags,
 189                         prefix_len_stat_func);
 190         return flags;
 191 }
 192
 193 #define USE_ONLY_LSTAT  0
 194
 195 /*
 196  * Return non-zero if path 'name' has a leading symlink component
 197  */
 198 int threaded_has_symlink_leading_path(struct cache_def *cache, const char *name, int len)
 199 {
 200         return lstat_cache(cache, name, len, FL_SYMLINK|FL_DIR, USE_ONLY_LSTAT) & FL_SYMLINK;
 201 }
 202
 203 /*
 204  * Return non-zero if path 'name' has a leading symlink component
 205  */
 206 int has_symlink_leading_path(const char *name, int len)
 207 {
 208         return threaded_has_symlink_leading_path(&default_cache, name, len);
 209 }
 210
 211 /*
 212  * Return zero if path 'name' has a leading symlink component or
 213  * if some leading path component does not exists.
 214  *
 215  * Return -1 if leading path exists and is a directory.
 216  *
 217  * Return path length if leading path exists and is neither a
 218  * directory nor a symlink.
 219  */
 220 int check_leading_path(const char *name, int len)
 221 {
 222         struct cache_def *cache = &default_cache;       /* FIXME */
 223         int flags;
 224         int match_len = lstat_cache_matchlen(cache, name, len, &flags,
 225                            FL_SYMLINK|FL_NOENT|FL_DIR, USE_ONLY_LSTAT);
 226         if (flags & (FL_SYMLINK|FL_NOENT))
 227                 return 0;
 228         else if (flags & FL_DIR)
 229                 return -1;
 230         else
 231                 return match_len;
 232 }
 233
 234 /*
 235  * Return non-zero if all path components of 'name' exists as a
 236  * directory.  If prefix_len > 0, we will test with the stat()
 237  * function instead of the lstat() function for a prefix length of
 238  * 'prefix_len', thus we then allow for symlinks in the prefix part as
 239  * long as those points to real existing directories.
 240  */
 241 int has_dirs_only_path(const char *name, int len, int prefix_len)
 242 {
 243         struct cache_def *cache = &default_cache;       /* FIXME */
 244         return lstat_cache(cache, name, len,
 245                            FL_DIR|FL_FULLPATH, prefix_len) &
 246                 FL_DIR;
 247 }
 248
 249 static struct removal_def {
 250         char path[PATH_MAX];
 251         int len;
 252 } removal;
 253
 254 static void do_remove_scheduled_dirs(int new_len)
 255 {
 256         while (removal.len > new_len) {
 257                 removal.path[removal.len] = '\0';
 258                 if (rmdir(removal.path))
 259                         break;
 260                 do {
 261                         removal.len--;
 262                 } while (removal.len > new_len &&
 263                          removal.path[removal.len] != '/');
 264         }
 265         removal.len = new_len;
 266 }
 267
 268 void schedule_dir_for_removal(const char *name, int len)
 269 {
 270         int match_len, last_slash, i, previous_slash;
 271
 272         match_len = last_slash = i =
 273                 longest_path_match(name, len, removal.path, removal.len,
 274                                    &previous_slash);
 275         /* Find last slash inside 'name' */
 276         while (i < len) {
 277                 if (name[i] == '/')
 278                         last_slash = i;
 279                 i++;
 280         }
 281
 282         /*
 283          * If we are about to go down the directory tree, we check if
 284          * we must first go upwards the tree, such that we then can
 285          * remove possible empty directories as we go upwards.
 286          */
 287         if (match_len < last_slash && match_len < removal.len)
 288                 do_remove_scheduled_dirs(match_len);
 289         /*
 290          * If we go deeper down the directory tree, we only need to
 291          * save the new path components as we go down.
 292          */
 293         if (match_len < last_slash) {
 294                 memcpy(&removal.path[match_len], &name[match_len],
 295                        last_slash - match_len);
 296                 removal.len = last_slash;
 297         }
 298 }
 299
 300 void remove_scheduled_dirs(void)
 301 {
 302         do_remove_scheduled_dirs(0);
 303 }