read-tree.c

   1 /*
   2  * GIT - The information manager from hell
   3  *
   4  * Copyright (C) Linus Torvalds, 2005
   5  */
   6 #include "cache.h"
   7
   8 static int stage = 0;
   9
  10 static int read_one_entry(unsigned char *sha1, const char *base, int baselen, const char *pathname, unsigned mode)
  11 {
  12         int len = strlen(pathname);
  13         unsigned int size = cache_entry_size(baselen + len);
  14         struct cache_entry *ce = malloc(size);
  15
  16         memset(ce, 0, size);
  17
  18         ce->ce_mode = create_ce_mode(mode);
  19         ce->ce_flags = create_ce_flags(baselen + len, stage);
  20         memcpy(ce->name, base, baselen);
  21         memcpy(ce->name + baselen, pathname, len+1);
  22         memcpy(ce->sha1, sha1, 20);
  23         return add_cache_entry(ce, 1);
  24 }
  25
  26 static int read_tree(unsigned char *sha1, const char *base, int baselen)
  27 {
  28         void *buffer;
  29         unsigned long size;
  30         char type[20];
  31
  32         buffer = read_sha1_file(sha1, type, &size);
  33         if (!buffer)
  34                 return -1;
  35         if (strcmp(type, "tree"))
  36                 return -1;
  37         while (size) {
  38                 int len = strlen(buffer)+1;
  39                 unsigned char *sha1 = buffer + len;
  40                 char *path = strchr(buffer, ' ')+1;
  41                 unsigned int mode;
  42
  43                 if (size < len + 20 || sscanf(buffer, "%o", &mode) != 1)
  44                         return -1;
  45
  46                 buffer = sha1 + 20;
  47                 size -= len + 20;
  48
  49                 if (S_ISDIR(mode)) {
  50                         int retval;
  51                         int pathlen = strlen(path);
  52                         char *newbase = malloc(baselen + 1 + pathlen);
  53                         memcpy(newbase, base, baselen);
  54                         memcpy(newbase + baselen, path, pathlen);
  55                         newbase[baselen + pathlen] = '/';
  56                         retval = read_tree(sha1, newbase, baselen + pathlen + 1);
  57                         free(newbase);
  58                         if (retval)
  59                                 return -1;
  60                         continue;
  61                 }
  62                 if (read_one_entry(sha1, base, baselen, path, mode) < 0)
  63                         return -1;
  64         }
  65         return 0;
  66 }
  67
  68 static int remove_lock = 0;
  69
  70 static void remove_lock_file(void)
  71 {
  72         if (remove_lock)
  73                 unlink(".git/index.lock");
  74 }
  75
  76 static int path_matches(struct cache_entry *a, struct cache_entry *b)
  77 {
  78         int len = ce_namelen(a);
  79         return ce_namelen(b) == len &&
  80                 !memcmp(a->name, b->name, len);
  81 }
  82
  83 static int same(struct cache_entry *a, struct cache_entry *b)
  84 {
  85         return a->ce_mode == b->ce_mode &&
  86                 !memcmp(a->sha1, b->sha1, 20);
  87 }
  88
  89
  90 /*
  91  * This removes all trivial merges that don't change the tree
  92  * and collapses them to state 0.
  93  *
  94  * _Any_ other merge is left to user policy.  That includes "both
  95  * created the same file", and "both removed the same file" - which are
  96  * trivial, but the user might still want to _note_ it.
  97  */
  98 static struct cache_entry *merge_entries(struct cache_entry *a,
  99                                          struct cache_entry *b,
 100                                          struct cache_entry *c)
 101 {
 102         int len = ce_namelen(a);
 103
 104         /*
 105          * Are they all the same filename? We won't do
 106          * any name merging
 107          */
 108         if (ce_namelen(b) != len ||
 109             ce_namelen(c) != len ||
 110             memcmp(a->name, b->name, len) ||
 111             memcmp(a->name, c->name, len))
 112                 return NULL;
 113
 114         /*
 115          * Ok, all three entries describe the same
 116          * filename, but maybe the contents or file
 117          * mode have changed?
 118          *
 119          * The trivial cases end up being the ones where two
 120          * out of three files are the same:
 121          *  - both destinations the same, trivially take either
 122          *  - one of the destination versions hasn't changed,
 123          *    take the other.
 124          *
 125          * The "all entries exactly the same" case falls out as
 126          * a special case of any of the "two same" cases.
 127          *
 128          * Here "a" is "original", and "b" and "c" are the two
 129          * trees we are merging.
 130          */
 131         if (same(b,c))
 132                 return c;
 133         if (same(a,b))
 134                 return c;
 135         if (same(a,c))
 136                 return b;
 137         return NULL;
 138 }
 139
 140 static void trivially_merge_cache(struct cache_entry **src, int nr)
 141 {
 142         static struct cache_entry null_entry;
 143         struct cache_entry **dst = src;
 144         struct cache_entry *old = &null_entry;
 145
 146         while (nr) {
 147                 struct cache_entry *ce, *result;
 148
 149                 ce = src[0];
 150
 151                 /* We throw away original cache entries except for the stat information */
 152                 if (!ce_stage(ce)) {
 153                         old = ce;
 154                         src++;
 155                         nr--;
 156                         active_nr--;
 157                         continue;
 158                 }
 159                 if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
 160                         /*
 161                          * See if we can re-use the old CE directly?
 162                          * That way we get the uptodate stat info.
 163                          */
 164                         if (path_matches(result, old) && same(result, old))
 165                                 *result = *old;
 166                         ce = result;
 167                         ce->ce_flags &= ~htons(CE_STAGEMASK);
 168                         src += 2;
 169                         nr -= 2;
 170                         active_nr -= 2;
 171                 }
 172                 *dst++ = ce;
 173                 src++;
 174                 nr--;
 175         }
 176 }
 177
 178 static void merge_stat_info(struct cache_entry **src, int nr)
 179 {
 180         static struct cache_entry null_entry;
 181         struct cache_entry **dst = src;
 182         struct cache_entry *old = &null_entry;
 183
 184         while (nr) {
 185                 struct cache_entry *ce;
 186
 187                 ce = src[0];
 188
 189                 /* We throw away original cache entries except for the stat information */
 190                 if (!ce_stage(ce)) {
 191                         old = ce;
 192                         src++;
 193                         nr--;
 194                         active_nr--;
 195                         continue;
 196                 }
 197                 if (path_matches(ce, old) && same(ce, old))
 198                         *ce = *old;
 199                 ce->ce_flags &= ~htons(CE_STAGEMASK);
 200                 *dst++ = ce;
 201                 src++;
 202                 nr--;
 203         }
 204 }
 205
 206 int main(int argc, char **argv)
 207 {
 208         int i, newfd, merge;
 209         unsigned char sha1[20];
 210
 211         newfd = open(".git/index.lock", O_RDWR | O_CREAT | O_EXCL, 0600);
 212         if (newfd < 0)
 213                 die("unable to create new cachefile");
 214         atexit(remove_lock_file);
 215         remove_lock = 1;
 216
 217         merge = 0;
 218         for (i = 1; i < argc; i++) {
 219                 const char *arg = argv[i];
 220
 221                 /* "-m" stands for "merge", meaning we start in stage 1 */
 222                 if (!strcmp(arg, "-m")) {
 223                         int i;
 224                         if (stage)
 225                                 usage("-m needs to come first");
 226                         read_cache();
 227                         for (i = 0; i < active_nr; i++) {
 228                                 if (ce_stage(active_cache[i]))
 229                                         usage("you need to resolve your current index first");
 230                         }
 231                         stage = 1;
 232                         merge = 1;
 233                         continue;
 234                 }
 235                 if (get_sha1_hex(arg, sha1) < 0)
 236                         usage("read-tree [-m] <sha1>");
 237                 if (stage > 3)
 238                         usage("can't merge more than two trees");
 239                 if (read_tree(sha1, "", 0) < 0)
 240                         die("failed to unpack tree object %s", arg);
 241                 stage++;
 242         }
 243         if (merge) {
 244                 switch (stage) {
 245                 case 4: /* Three-way merge */
 246                         trivially_merge_cache(active_cache, active_nr);
 247                         break;
 248                 case 2: /* Just read a tree, merge with old cache contents */
 249                         merge_stat_info(active_cache, active_nr);
 250                         break;
 251                 default:
 252                         die("just how do you expect me to merge %d trees?", stage-1);
 253                 }
 254         }
 255         if (write_cache(newfd, active_cache, active_nr) ||
 256             rename(".git/index.lock", ".git/index"))
 257                 die("unable to write new index file");
 258         remove_lock = 0;
 259         return 0;
 260 }