multi-pack-index: load into memory

diff --git a/midx.c b/midx.c
index f85f2d334d4762119f403d8a42292486e15640aa..c1ff5acf853911eb66760c74c7484841240e0ccd 100644 (file)
--- a/midx.c
+++ b/midx.c
@@ -1,18 +1,97 @@
 #include "cache.h"
 #include "csum-file.h"
 #include "lockfile.h"
+#include "object-store.h"
 #include "midx.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
+#define MIDX_BYTE_FILE_VERSION 4
+#define MIDX_BYTE_HASH_VERSION 5
+#define MIDX_BYTE_NUM_CHUNKS 6
+#define MIDX_BYTE_NUM_PACKS 8
 #define MIDX_HASH_VERSION 1
 #define MIDX_HEADER_SIZE 12
+#define MIDX_HASH_LEN 20
+#define MIDX_MIN_SIZE (MIDX_HEADER_SIZE + MIDX_HASH_LEN)
 
 static char *get_midx_filename(const char *object_dir)
 {
        return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }
 
+struct multi_pack_index *load_multi_pack_index(const char *object_dir)
+{
+       struct multi_pack_index *m = NULL;
+       int fd;
+       struct stat st;
+       size_t midx_size;
+       void *midx_map = NULL;
+       uint32_t hash_version;
+       char *midx_name = get_midx_filename(object_dir);
+
+       fd = git_open(midx_name);
+
+       if (fd < 0)
+               goto cleanup_fail;
+       if (fstat(fd, &st)) {
+               error_errno(_("failed to read %s"), midx_name);
+               goto cleanup_fail;
+       }
+
+       midx_size = xsize_t(st.st_size);
+
+       if (midx_size < MIDX_MIN_SIZE) {
+               error(_("multi-pack-index file %s is too small"), midx_name);
+               goto cleanup_fail;
+       }
+
+       FREE_AND_NULL(midx_name);
+
+       midx_map = xmmap(NULL, midx_size, PROT_READ, MAP_PRIVATE, fd, 0);
+
+       FLEX_ALLOC_MEM(m, object_dir, object_dir, strlen(object_dir));
+       m->fd = fd;
+       m->data = midx_map;
+       m->data_len = midx_size;
+
+       m->signature = get_be32(m->data);
+       if (m->signature != MIDX_SIGNATURE) {
+               error(_("multi-pack-index signature 0x%08x does not match signature 0x%08x"),
+                     m->signature, MIDX_SIGNATURE);
+               goto cleanup_fail;
+       }
+
+       m->version = m->data[MIDX_BYTE_FILE_VERSION];
+       if (m->version != MIDX_VERSION) {
+               error(_("multi-pack-index version %d not recognized"),
+                     m->version);
+               goto cleanup_fail;
+       }
+
+       hash_version = m->data[MIDX_BYTE_HASH_VERSION];
+       if (hash_version != MIDX_HASH_VERSION) {
+               error(_("hash version %u does not match"), hash_version);
+               goto cleanup_fail;
+       }
+       m->hash_len = MIDX_HASH_LEN;
+
+       m->num_chunks = m->data[MIDX_BYTE_NUM_CHUNKS];
+
+       m->num_packs = get_be32(m->data + MIDX_BYTE_NUM_PACKS);
+
+       return m;
+
+cleanup_fail:
+       free(m);
+       free(midx_name);
+       if (midx_map)
+               munmap(midx_map, midx_size);
+       if (0 <= fd)
+               close(fd);
+       return NULL;
+}
+
 static size_t write_midx_header(struct hashfile *f,
                                unsigned char num_chunks,
                                uint32_t num_packs)