+struct diff_filespec *alloc_filespec(const char *path)
+{
+ int namelen = strlen(path);
+ struct diff_filespec *spec = xmalloc(sizeof(*spec) + namelen + 1);
+ spec->path = (char *)(spec + 1);
+ strcpy(spec->path, path);
+ spec->should_free = spec->should_munmap = spec->file_valid = 0;
+ spec->xfrm_flags = 0;
+ spec->size = 0;
+ spec->data = 0;
+ return spec;
+}
+
+void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
+ unsigned short mode)
+{
+ spec->mode = mode;
+ memcpy(spec->sha1, sha1, 20);
+ spec->sha1_valid = !!memcmp(sha1, null_sha1, 20);
+ spec->file_valid = 1;
+}
+
+/*
+ * Given a name and sha1 pair, if the dircache tells us the file in
+ * the work tree has that object contents, return true, so that
+ * prepare_temp_file() does not have to inflate and extract.
+ */
+static int work_tree_matches(const char *name, const unsigned char *sha1)
+{
+ struct cache_entry *ce;
+ struct stat st;
+ int pos, len;
+
+ /* We do not read the cache ourselves here, because the
+ * benchmark with my previous version that always reads cache
+ * shows that it makes things worse for diff-tree comparing
+ * two linux-2.6 kernel trees in an already checked out work
+ * tree. This is because most diff-tree comparisons deal with
+ * only a small number of files, while reading the cache is
+ * expensive for a large project, and its cost outweighs the
+ * savings we get by not inflating the object to a temporary
+ * file. Practically, this code only helps when we are used
+ * by diff-cache --cached, which does read the cache before
+ * calling us.
+ */
+ if (!active_cache)
+ return 0;
+
+ len = strlen(name);
+ pos = cache_name_pos(name, len);
+ if (pos < 0)
+ return 0;
+ ce = active_cache[pos];
+ if ((lstat(name, &st) < 0) ||
+ !S_ISREG(st.st_mode) || /* careful! */
+ ce_match_stat(ce, &st) ||
+ memcmp(sha1, ce->sha1, 20))
+ return 0;
+ /* we return 1 only when we can stat, it is a regular file,
+ * stat information matches, and sha1 recorded in the cache
+ * matches. I.e. we know the file in the work tree really is
+ * the same as the <name, sha1> pair.
+ */
+ return 1;
+}
+
+/*
+ * While doing rename detection and pickaxe operation, we may need to
+ * grab the data for the blob (or file) for our own in-core comparison.
+ * diff_filespec has data and size fields for this purpose.
+ */
+int diff_populate_filespec(struct diff_filespec *s)
+{
+ int err = 0;
+ if (!s->file_valid)
+ die("internal error: asking to populate invalid file.");
+ if (S_ISDIR(s->mode))
+ return -1;
+
+ if (s->data)
+ return err;
+ if (!s->sha1_valid ||
+ work_tree_matches(s->path, s->sha1)) {
+ struct stat st;
+ int fd;
+ if (lstat(s->path, &st) < 0) {
+ if (errno == ENOENT) {
+ err_empty:
+ err = -1;
+ empty:
+ s->data = "";
+ s->size = 0;
+ return err;
+ }
+ }
+ s->size = st.st_size;
+ if (!s->size)
+ goto empty;
+ if (S_ISLNK(st.st_mode)) {
+ int ret;
+ s->data = xmalloc(s->size);
+ s->should_free = 1;
+ ret = readlink(s->path, s->data, s->size);
+ if (ret < 0) {
+ free(s->data);
+ goto err_empty;
+ }
+ return 0;
+ }
+ fd = open(s->path, O_RDONLY);
+ if (fd < 0)
+ goto err_empty;
+ s->data = mmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
+ s->should_munmap = 1;
+ close(fd);
+ }
+ else {
+ char type[20];
+ s->data = read_sha1_file(s->sha1, type, &s->size);
+ s->should_free = 1;
+ }
+ return 0;
+}
+
+void diff_free_filespec_data(struct diff_filespec *s)
+{
+ if (s->should_free)
+ free(s->data);
+ else if (s->should_munmap)
+ munmap(s->data, s->size);
+ s->should_free = s->should_munmap = 0;
+ s->data = 0;
+}
+
+static void prep_temp_blob(struct diff_tempfile *temp,
+ void *blob,
+ unsigned long size,
+ unsigned char *sha1,
+ int mode)
+{
+ int fd;
+
+ strcpy(temp->tmp_path, ".diff_XXXXXX");
+ fd = mkstemp(temp->tmp_path);
+ if (fd < 0)
+ die("unable to create temp-file");
+ if (write(fd, blob, size) != size)
+ die("unable to write temp-file");
+ close(fd);
+ temp->name = temp->tmp_path;
+ strcpy(temp->hex, sha1_to_hex(sha1));
+ temp->hex[40] = 0;
+ sprintf(temp->mode, "%06o", mode);
+}
+