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