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(struct cache_def *cache, const char *name, int len,
  68                        int track_flags, int prefix_len_stat_func)
  69 {
  70         int match_len, last_slash, last_slash_dir, previous_slash;
  71         int match_flags, ret_flags, save_flags, max_len, ret;
  72         struct stat st;
  73
  74         if (cache->track_flags != track_flags ||
  75             cache->prefix_len_stat_func != prefix_len_stat_func) {
  76                 /*
  77                  * As a safeguard rule we clear the cache if the
  78                  * values of track_flags and/or prefix_len_stat_func
  79                  * does not match with the last supplied values.
  80                  */
  81                 reset_lstat_cache(cache);
  82                 cache->track_flags = track_flags;
  83                 cache->prefix_len_stat_func = prefix_len_stat_func;
  84                 match_len = last_slash = 0;
  85         } else {
  86                 /*
  87                  * Check to see if we have a match from the cache for
  88                  * the 2 "excluding" path types.
  89                  */
  90                 match_len = last_slash =
  91                         longest_path_match(name, len, cache->path, cache->len,
  92                                            &previous_slash);
  93                 match_flags = cache->flags & track_flags & (FL_NOENT|FL_SYMLINK);
  94
  95                 if (!(track_flags & FL_FULLPATH) && match_len == len)
  96                         match_len = last_slash = previous_slash;
  97
  98                 if (match_flags && match_len == cache->len)
  99                         return match_flags;
 100                 /*
 101                  * If we now have match_len > 0, we would know that
 102                  * the matched part will always be a directory.
 103                  *
 104                  * Also, if we are tracking directories and 'name' is
 105                  * a substring of the cache on a path component basis,
 106                  * we can return immediately.
 107                  */
 108                 match_flags = track_flags & FL_DIR;
 109                 if (match_flags && len == match_len)
 110                         return match_flags;
 111         }
 112
 113         /*
 114          * Okay, no match from the cache so far, so now we have to
 115          * check the rest of the path components.
 116          */
 117         ret_flags = FL_DIR;
 118         last_slash_dir = last_slash;
 119         max_len = len < PATH_MAX ? len : PATH_MAX;
 120         while (match_len < max_len) {
 121                 do {
 122                         cache->path[match_len] = name[match_len];
 123                         match_len++;
 124                 } while (match_len < max_len && name[match_len] != '/');
 125                 if (match_len >= max_len && !(track_flags & FL_FULLPATH))
 126                         break;
 127                 last_slash = match_len;
 128                 cache->path[last_slash] = '\0';
 129
 130                 if (last_slash <= prefix_len_stat_func)
 131                         ret = stat(cache->path, &st);
 132                 else
 133                         ret = lstat(cache->path, &st);
 134
 135                 if (ret) {
 136                         ret_flags = FL_LSTATERR;
 137                         if (errno == ENOENT)
 138                                 ret_flags |= FL_NOENT;
 139                 } else if (S_ISDIR(st.st_mode)) {
 140                         last_slash_dir = last_slash;
 141                         continue;
 142                 } else if (S_ISLNK(st.st_mode)) {
 143                         ret_flags = FL_SYMLINK;
 144                 } else {
 145                         ret_flags = FL_ERR;
 146                 }
 147                 break;
 148         }
 149
 150         /*
 151          * At the end update the cache.  Note that max 3 different
 152          * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached
 153          * for the moment!
 154          */
 155         save_flags = ret_flags & track_flags & (FL_NOENT|FL_SYMLINK);
 156         if (save_flags && last_slash > 0 && last_slash <= PATH_MAX) {
 157                 cache->path[last_slash] = '\0';
 158                 cache->len = last_slash;
 159                 cache->flags = save_flags;
 160         } else if ((track_flags & FL_DIR) &&
 161                    last_slash_dir > 0 && last_slash_dir <= PATH_MAX) {
 162                 /*
 163                  * We have a separate test for the directory case,
 164                  * since it could be that we have found a symlink or a
 165                  * non-existing directory and the track_flags says
 166                  * that we cannot cache this fact, so the cache would
 167                  * then have been left empty in this case.
 168                  *
 169                  * But if we are allowed to track real directories, we
 170                  * can still cache the path components before the last
 171                  * one (the found symlink or non-existing component).
 172                  */
 173                 cache->path[last_slash_dir] = '\0';
 174                 cache->len = last_slash_dir;
 175                 cache->flags = FL_DIR;
 176         } else {
 177                 reset_lstat_cache(cache);
 178         }
 179         return ret_flags;
 180 }
 181
 182 #define USE_ONLY_LSTAT  0
 183
 184 /*
 185  * Return non-zero if path 'name' has a leading symlink component
 186  */
 187 int threaded_has_symlink_leading_path(struct cache_def *cache, const char *name, int len)
 188 {
 189         return lstat_cache(cache, name, len, FL_SYMLINK|FL_DIR, USE_ONLY_LSTAT) & FL_SYMLINK;
 190 }
 191
 192 /*
 193  * Return non-zero if path 'name' has a leading symlink component
 194  */
 195 int has_symlink_leading_path(const char *name, int len)
 196 {
 197         return threaded_has_symlink_leading_path(&default_cache, name, len);
 198 }
 199
 200 /*
 201  * Return non-zero if path 'name' has a leading symlink component or
 202  * if some leading path component does not exists.
 203  */
 204 int has_symlink_or_noent_leading_path(const char *name, int len)
 205 {
 206         struct cache_def *cache = &default_cache;       /* FIXME */
 207         return lstat_cache(cache, name, len,
 208                            FL_SYMLINK|FL_NOENT|FL_DIR, USE_ONLY_LSTAT) &
 209                 (FL_SYMLINK|FL_NOENT);
 210 }
 211
 212 /*
 213  * Return non-zero if all path components of 'name' exists as a
 214  * directory.  If prefix_len > 0, we will test with the stat()
 215  * function instead of the lstat() function for a prefix length of
 216  * 'prefix_len', thus we then allow for symlinks in the prefix part as
 217  * long as those points to real existing directories.
 218  */
 219 int has_dirs_only_path(const char *name, int len, int prefix_len)
 220 {
 221         struct cache_def *cache = &default_cache;       /* FIXME */
 222         return lstat_cache(cache, name, len,
 223                            FL_DIR|FL_FULLPATH, prefix_len) &
 224                 FL_DIR;
 225 }
 226
 227 static struct removal_def {
 228         char path[PATH_MAX];
 229         int len;
 230 } removal;
 231
 232 static void do_remove_scheduled_dirs(int new_len)
 233 {
 234         while (removal.len > new_len) {
 235                 removal.path[removal.len] = '\0';
 236                 if (rmdir(removal.path))
 237                         break;
 238                 do {
 239                         removal.len--;
 240                 } while (removal.len > new_len &&
 241                          removal.path[removal.len] != '/');
 242         }
 243         removal.len = new_len;
 244 }
 245
 246 void schedule_dir_for_removal(const char *name, int len)
 247 {
 248         int match_len, last_slash, i, previous_slash;
 249
 250         match_len = last_slash = i =
 251                 longest_path_match(name, len, removal.path, removal.len,
 252                                    &previous_slash);
 253         /* Find last slash inside 'name' */
 254         while (i < len) {
 255                 if (name[i] == '/')
 256                         last_slash = i;
 257                 i++;
 258         }
 259
 260         /*
 261          * If we are about to go down the directory tree, we check if
 262          * we must first go upwards the tree, such that we then can
 263          * remove possible empty directories as we go upwards.
 264          */
 265         if (match_len < last_slash && match_len < removal.len)
 266                 do_remove_scheduled_dirs(match_len);
 267         /*
 268          * If we go deeper down the directory tree, we only need to
 269          * save the new path components as we go down.
 270          */
 271         if (match_len < last_slash) {
 272                 memcpy(&removal.path[match_len], &name[match_len],
 273                        last_slash - match_len);
 274                 removal.len = last_slash;
 275         }
 276 }
 277
 278 void remove_scheduled_dirs(void)
 279 {
 280         do_remove_scheduled_dirs(0);
 281 }