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 unpack_tree(unsigned char *sha1)
  11 {
  12         void *buffer;
  13         unsigned long size;
  14         int ret;
  15
  16         buffer = read_object_with_reference(sha1, "tree", &size, NULL);
  17         if (!buffer)
  18                 return -1;
  19         ret = read_tree(buffer, size, stage);
  20         free(buffer);
  21         return ret;
  22 }
  23
  24 static char *lockfile_name;
  25
  26 static void remove_lock_file(void)
  27 {
  28         if (lockfile_name)
  29                 unlink(lockfile_name);
  30 }
  31
  32 static int path_matches(struct cache_entry *a, struct cache_entry *b)
  33 {
  34         int len = ce_namelen(a);
  35         return ce_namelen(b) == len &&
  36                 !memcmp(a->name, b->name, len);
  37 }
  38
  39 static int same(struct cache_entry *a, struct cache_entry *b)
  40 {
  41         return a->ce_mode == b->ce_mode &&
  42                 !memcmp(a->sha1, b->sha1, 20);
  43 }
  44
  45
  46 /*
  47  * This removes all trivial merges that don't change the tree
  48  * and collapses them to state 0.
  49  *
  50  * _Any_ other merge is left to user policy.  That includes "both
  51  * created the same file", and "both removed the same file" - which are
  52  * trivial, but the user might still want to _note_ it.
  53  */
  54 static struct cache_entry *merge_entries(struct cache_entry *a,
  55                                          struct cache_entry *b,
  56                                          struct cache_entry *c)
  57 {
  58         int len = ce_namelen(a);
  59
  60         /*
  61          * Are they all the same filename? We won't do
  62          * any name merging
  63          */
  64         if (ce_namelen(b) != len ||
  65             ce_namelen(c) != len ||
  66             memcmp(a->name, b->name, len) ||
  67             memcmp(a->name, c->name, len))
  68                 return NULL;
  69
  70         /*
  71          * Ok, all three entries describe the same
  72          * filename, but maybe the contents or file
  73          * mode have changed?
  74          *
  75          * The trivial cases end up being the ones where two
  76          * out of three files are the same:
  77          *  - both destinations the same, trivially take either
  78          *  - one of the destination versions hasn't changed,
  79          *    take the other.
  80          *
  81          * The "all entries exactly the same" case falls out as
  82          * a special case of any of the "two same" cases.
  83          *
  84          * Here "a" is "original", and "b" and "c" are the two
  85          * trees we are merging.
  86          */
  87         if (same(b,c))
  88                 return c;
  89         if (same(a,b))
  90                 return c;
  91         if (same(a,c))
  92                 return b;
  93         return NULL;
  94 }
  95
  96 static void trivially_merge_cache(struct cache_entry **src, int nr)
  97 {
  98         static struct cache_entry null_entry;
  99         struct cache_entry **dst = src;
 100         struct cache_entry *old = &null_entry;
 101
 102         while (nr) {
 103                 struct cache_entry *ce, *result;
 104
 105                 ce = src[0];
 106
 107                 /* We throw away original cache entries except for the stat information */
 108                 if (!ce_stage(ce)) {
 109                         old = ce;
 110                         src++;
 111                         nr--;
 112                         active_nr--;
 113                         continue;
 114                 }
 115                 if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
 116                         /*
 117                          * See if we can re-use the old CE directly?
 118                          * That way we get the uptodate stat info.
 119                          */
 120                         if (path_matches(result, old) && same(result, old))
 121                                 *result = *old;
 122                         ce = result;
 123                         ce->ce_flags &= ~htons(CE_STAGEMASK);
 124                         src += 2;
 125                         nr -= 2;
 126                         active_nr -= 2;
 127                 }
 128                 *dst++ = ce;
 129                 src++;
 130                 nr--;
 131         }
 132 }
 133
 134 static void merge_stat_info(struct cache_entry **src, int nr)
 135 {
 136         static struct cache_entry null_entry;
 137         struct cache_entry **dst = src;
 138         struct cache_entry *old = &null_entry;
 139
 140         while (nr) {
 141                 struct cache_entry *ce;
 142
 143                 ce = src[0];
 144
 145                 /* We throw away original cache entries except for the stat information */
 146                 if (!ce_stage(ce)) {
 147                         old = ce;
 148                         src++;
 149                         nr--;
 150                         active_nr--;
 151                         continue;
 152                 }
 153                 if (path_matches(ce, old) && same(ce, old))
 154                         *ce = *old;
 155                 ce->ce_flags &= ~htons(CE_STAGEMASK);
 156                 *dst++ = ce;
 157                 src++;
 158                 nr--;
 159         }
 160 }
 161
 162 static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> <sha3>])";
 163
 164 int main(int argc, char **argv)
 165 {
 166         int i, newfd, merge;
 167         unsigned char sha1[20];
 168         static char lockfile[MAXPATHLEN+1];
 169         const char *indexfile = get_index_file();
 170
 171         snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
 172
 173         newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
 174         if (newfd < 0)
 175                 die("unable to create new cachefile");
 176         atexit(remove_lock_file);
 177         lockfile_name = lockfile;
 178
 179         merge = 0;
 180         for (i = 1; i < argc; i++) {
 181                 const char *arg = argv[i];
 182
 183                 /* "-m" stands for "merge", meaning we start in stage 1 */
 184                 if (!strcmp(arg, "-m")) {
 185                         int i;
 186                         if (stage)
 187                                 die("-m needs to come first");
 188                         read_cache();
 189                         for (i = 0; i < active_nr; i++) {
 190                                 if (ce_stage(active_cache[i]))
 191                                         die("you need to resolve your current index first");
 192                         }
 193                         stage = 1;
 194                         merge = 1;
 195                         continue;
 196                 }
 197                 if (get_sha1(arg, sha1) < 0)
 198                         usage(read_tree_usage);
 199                 if (stage > 3)
 200                         usage(read_tree_usage);
 201                 if (unpack_tree(sha1) < 0)
 202                         die("failed to unpack tree object %s", arg);
 203                 stage++;
 204         }
 205         if (merge) {
 206                 switch (stage) {
 207                 case 4: /* Three-way merge */
 208                         trivially_merge_cache(active_cache, active_nr);
 209                         break;
 210                 case 2: /* Just read a tree, merge with old cache contents */
 211                         merge_stat_info(active_cache, active_nr);
 212                         break;
 213                 default:
 214                         die("just how do you expect me to merge %d trees?", stage-1);
 215                 }
 216         }
 217         if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
 218                 die("unable to write new index file");
 219         lockfile_name = NULL;
 220         return 0;
 221 }