unsigned int hdr_entries;
};
+/*
+ * Packed object index header
+ *
+ * struct pack_idx_header {
+ * uint32_t idx_signature;
+ * uint32_t idx_version;
+ * };
+ *
+ * Note: this header isn't active yet. In future versions of git
+ * we may change the index file format. At that time we would start
+ * the first four bytes of the new index format with this signature,
+ * as all older git binaries would find this value illegal and abort
+ * reading the file.
+ *
+ * This is the case because the number of objects in a packfile
+ * cannot exceed 1,431,660,000 as every object would need at least
+ * 3 bytes of data and the overall packfile cannot exceed 4 GiB due
+ * to the 32 bit offsets used by the index. Clearly the signature
+ * exceeds this maximum.
+ *
+ * Very old git binaries will also compare the first 4 bytes to the
+ * next 4 bytes in the index and abort with a "non-monotonic index"
+ * error if the second 4 byte word is smaller than the first 4
+ * byte word. This would be true in the proposed future index
+ * format as idx_signature would be greater than idx_version.
+ */
+#define PACK_IDX_SIGNATURE 0xff744f63 /* "\377tOc" */
+
extern int verify_pack(struct packed_git *, int);
#endif