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_recursive(void *buffer, const char *type,
  27                                unsigned long size,
  28                                const char *base, int baselen)
  29 {
  30         if (!buffer || strcmp(type, "tree"))
  31                 return -1;
  32         while (size) {
  33                 int len = strlen(buffer)+1;
  34                 unsigned char *sha1 = buffer + len;
  35                 char *path = strchr(buffer, ' ')+1;
  36                 unsigned int mode;
  37
  38                 if (size < len + 20 || sscanf(buffer, "%o", &mode) != 1)
  39                         return -1;
  40
  41                 buffer = sha1 + 20;
  42                 size -= len + 20;
  43
  44                 if (S_ISDIR(mode)) {
  45                         int retval;
  46                         int pathlen = strlen(path);
  47                         char *newbase = malloc(baselen + 1 + pathlen);
  48                         void *eltbuf;
  49                         char elttype[20];
  50                         unsigned long eltsize;
  51
  52                         eltbuf = read_sha1_file(sha1, elttype, &eltsize);
  53                         if (!eltbuf)
  54                                 return -1;
  55                         memcpy(newbase, base, baselen);
  56                         memcpy(newbase + baselen, path, pathlen);
  57                         newbase[baselen + pathlen] = '/';
  58                         retval = read_tree_recursive(eltbuf, elttype, eltsize,
  59                                                      newbase,
  60                                                      baselen + pathlen + 1);
  61                         free(eltbuf);
  62                         free(newbase);
  63                         if (retval)
  64                                 return -1;
  65                         continue;
  66                 }
  67                 if (read_one_entry(sha1, base, baselen, path, mode) < 0)
  68                         return -1;
  69         }
  70         return 0;
  71 }
  72
  73 static int read_tree(unsigned char *sha1, const char *base, int baselen)
  74 {
  75         void *buffer;
  76         unsigned long size;
  77
  78         buffer = read_tree_with_tree_or_commit_sha1(sha1, &size, 0);
  79         return read_tree_recursive(buffer, "tree", size, base, baselen);
  80 }
  81
  82 static int remove_lock = 0;
  83
  84 static void remove_lock_file(void)
  85 {
  86         if (remove_lock)
  87                 unlink(".git/index.lock");
  88 }
  89
  90 static int path_matches(struct cache_entry *a, struct cache_entry *b)
  91 {
  92         int len = ce_namelen(a);
  93         return ce_namelen(b) == len &&
  94                 !memcmp(a->name, b->name, len);
  95 }
  96
  97 static int same(struct cache_entry *a, struct cache_entry *b)
  98 {
  99         return a->ce_mode == b->ce_mode &&
 100                 !memcmp(a->sha1, b->sha1, 20);
 101 }
 102
 103
 104 /*
 105  * This removes all trivial merges that don't change the tree
 106  * and collapses them to state 0.
 107  *
 108  * _Any_ other merge is left to user policy.  That includes "both
 109  * created the same file", and "both removed the same file" - which are
 110  * trivial, but the user might still want to _note_ it.
 111  */
 112 static struct cache_entry *merge_entries(struct cache_entry *a,
 113                                          struct cache_entry *b,
 114                                          struct cache_entry *c)
 115 {
 116         int len = ce_namelen(a);
 117
 118         /*
 119          * Are they all the same filename? We won't do
 120          * any name merging
 121          */
 122         if (ce_namelen(b) != len ||
 123             ce_namelen(c) != len ||
 124             memcmp(a->name, b->name, len) ||
 125             memcmp(a->name, c->name, len))
 126                 return NULL;
 127
 128         /*
 129          * Ok, all three entries describe the same
 130          * filename, but maybe the contents or file
 131          * mode have changed?
 132          *
 133          * The trivial cases end up being the ones where two
 134          * out of three files are the same:
 135          *  - both destinations the same, trivially take either
 136          *  - one of the destination versions hasn't changed,
 137          *    take the other.
 138          *
 139          * The "all entries exactly the same" case falls out as
 140          * a special case of any of the "two same" cases.
 141          *
 142          * Here "a" is "original", and "b" and "c" are the two
 143          * trees we are merging.
 144          */
 145         if (same(b,c))
 146                 return c;
 147         if (same(a,b))
 148                 return c;
 149         if (same(a,c))
 150                 return b;
 151         return NULL;
 152 }
 153
 154 static void trivially_merge_cache(struct cache_entry **src, int nr)
 155 {
 156         static struct cache_entry null_entry;
 157         struct cache_entry **dst = src;
 158         struct cache_entry *old = &null_entry;
 159
 160         while (nr) {
 161                 struct cache_entry *ce, *result;
 162
 163                 ce = src[0];
 164
 165                 /* We throw away original cache entries except for the stat information */
 166                 if (!ce_stage(ce)) {
 167                         old = ce;
 168                         src++;
 169                         nr--;
 170                         active_nr--;
 171                         continue;
 172                 }
 173                 if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
 174                         /*
 175                          * See if we can re-use the old CE directly?
 176                          * That way we get the uptodate stat info.
 177                          */
 178                         if (path_matches(result, old) && same(result, old))
 179                                 *result = *old;
 180                         ce = result;
 181                         ce->ce_flags &= ~htons(CE_STAGEMASK);
 182                         src += 2;
 183                         nr -= 2;
 184                         active_nr -= 2;
 185                 }
 186                 *dst++ = ce;
 187                 src++;
 188                 nr--;
 189         }
 190 }
 191
 192 static void merge_stat_info(struct cache_entry **src, int nr)
 193 {
 194         static struct cache_entry null_entry;
 195         struct cache_entry **dst = src;
 196         struct cache_entry *old = &null_entry;
 197
 198         while (nr) {
 199                 struct cache_entry *ce;
 200
 201                 ce = src[0];
 202
 203                 /* We throw away original cache entries except for the stat information */
 204                 if (!ce_stage(ce)) {
 205                         old = ce;
 206                         src++;
 207                         nr--;
 208                         active_nr--;
 209                         continue;
 210                 }
 211                 if (path_matches(ce, old) && same(ce, old))
 212                         *ce = *old;
 213                 ce->ce_flags &= ~htons(CE_STAGEMASK);
 214                 *dst++ = ce;
 215                 src++;
 216                 nr--;
 217         }
 218 }
 219
 220 int main(int argc, char **argv)
 221 {
 222         int i, newfd, merge;
 223         unsigned char sha1[20];
 224
 225         newfd = open(".git/index.lock", O_RDWR | O_CREAT | O_EXCL, 0600);
 226         if (newfd < 0)
 227                 die("unable to create new cachefile");
 228         atexit(remove_lock_file);
 229         remove_lock = 1;
 230
 231         merge = 0;
 232         for (i = 1; i < argc; i++) {
 233                 const char *arg = argv[i];
 234
 235                 /* "-m" stands for "merge", meaning we start in stage 1 */
 236                 if (!strcmp(arg, "-m")) {
 237                         int i;
 238                         if (stage)
 239                                 usage("-m needs to come first");
 240                         read_cache();
 241                         for (i = 0; i < active_nr; i++) {
 242                                 if (ce_stage(active_cache[i]))
 243                                         usage("you need to resolve your current index first");
 244                         }
 245                         stage = 1;
 246                         merge = 1;
 247                         continue;
 248                 }
 249                 if (get_sha1_hex(arg, sha1) < 0)
 250                         usage("read-tree [-m] <sha1>");
 251                 if (stage > 3)
 252                         usage("can't merge more than two trees");
 253                 if (read_tree(sha1, "", 0) < 0)
 254                         die("failed to unpack tree object %s", arg);
 255                 stage++;
 256         }
 257         if (merge) {
 258                 switch (stage) {
 259                 case 4: /* Three-way merge */
 260                         trivially_merge_cache(active_cache, active_nr);
 261                         break;
 262                 case 2: /* Just read a tree, merge with old cache contents */
 263                         merge_stat_info(active_cache, active_nr);
 264                         break;
 265                 default:
 266                         die("just how do you expect me to merge %d trees?", stage-1);
 267                 }
 268         }
 269         if (write_cache(newfd, active_cache, active_nr) ||
 270             rename(".git/index.lock", ".git/index"))
 271                 die("unable to write new index file");
 272         remove_lock = 0;
 273         return 0;
 274 }