[PATCH 01/16] Modify cache_header to prepare for other index formats

[Thomas Gummerer <t.gummerer@gmail.com>]

Modify the cache_header such that other index file formats
can be added and reusing the common part of each index format.

The signature and version have to be present in every
version of the index file format, to check if it can be read
by a specific version of git, while other entries (eg. number
of entries for index v2/3/4) can be different from one file
format to another. Therefore it is split to its own struct.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---
 cache.h              |  5 ++++-
 read-cache.c         | 20 +++++++++++++-------
 test-index-version.c |  2 +-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/cache.h b/cache.h
index 6e9a243..d4028ef 100644
--- a/cache.h
+++ b/cache.h
@@ -99,9 +99,12 @@ unsigned long git_deflate_bound(git_zstream *, unsigned long);
  */
 
 #define CACHE_SIGNATURE 0x44495243	/* "DIRC" */
-struct cache_header {
+struct cache_version_header {
 	unsigned int hdr_signature;
 	unsigned int hdr_version;
+};
+
+struct cache_header_v2 {
 	unsigned int hdr_entries;
 };
 
diff --git a/read-cache.c b/read-cache.c
index ab00d02..c44b5f7 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1247,7 +1247,7 @@ struct ondisk_cache_entry_extended {
 			    ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
 			    ondisk_cache_entry_size(ce_namelen(ce)))
 
-static int verify_hdr(struct cache_header *hdr, unsigned long size)
+static int verify_hdr(struct cache_version_header *hdr, unsigned long size)
 {
 	git_SHA_CTX c;
 	unsigned char sha1[20];
@@ -1409,7 +1409,8 @@ int read_index_from(struct index_state *istate, const char *path)
 	int fd, i;
 	struct stat st;
 	unsigned long src_offset;
-	struct cache_header *hdr;
+	struct cache_version_header *hdr;
+	struct cache_header_v2 *hdr_v2;
 	void *mmap;
 	size_t mmap_size;
 	struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
@@ -1433,7 +1434,7 @@ int read_index_from(struct index_state *istate, const char *path)
 
 	errno = EINVAL;
 	mmap_size = xsize_t(st.st_size);
-	if (mmap_size < sizeof(struct cache_header) + 20)
+	if (mmap_size < sizeof(struct cache_version_header) + 20)
 		die("index file smaller than expected");
 
 	mmap = xmmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
@@ -1442,11 +1443,13 @@ int read_index_from(struct index_state *istate, const char *path)
 		die_errno("unable to map index file");
 
 	hdr = mmap;
+	hdr_v2 =  mmap + sizeof(*hdr);
 	if (verify_hdr(hdr, mmap_size) < 0)
 		goto unmap;
 
+	hdr_v2 = mmap + sizeof(*hdr);
 	istate->version = ntohl(hdr->hdr_version);
-	istate->cache_nr = ntohl(hdr->hdr_entries);
+	istate->cache_nr = ntohl(hdr_v2->hdr_entries);
 	istate->cache_alloc = alloc_nr(istate->cache_nr);
 	istate->cache = xcalloc(istate->cache_alloc, sizeof(struct cache_entry *));
 	istate->initialized = 1;
@@ -1456,7 +1459,7 @@ int read_index_from(struct index_state *istate, const char *path)
 	else
 		previous_name = NULL;
 
-	src_offset = sizeof(*hdr);
+	src_offset = sizeof(*hdr) + sizeof(*hdr_v2);
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct ondisk_cache_entry *disk_ce;
 		struct cache_entry *ce;
@@ -1757,7 +1760,8 @@ void update_index_if_able(struct index_state *istate, struct lock_file *lockfile
 int write_index(struct index_state *istate, int newfd)
 {
 	git_SHA_CTX c;
-	struct cache_header hdr;
+	struct cache_version_header hdr;
+	struct cache_header_v2 hdr_v2;
 	int i, err, removed, extended, hdr_version;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
@@ -1787,11 +1791,13 @@ int write_index(struct index_state *istate, int newfd)
 
 	hdr.hdr_signature = htonl(CACHE_SIGNATURE);
 	hdr.hdr_version = htonl(hdr_version);
-	hdr.hdr_entries = htonl(entries - removed);
+	hdr_v2.hdr_entries = htonl(entries - removed);
 
 	git_SHA1_Init(&c);
 	if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
 		return -1;
+	if (ce_write(&c, newfd, &hdr_v2, sizeof(hdr_v2)) < 0)
+		return -1;
 
 	previous_name = (hdr_version == 4) ? &previous_name_buf : NULL;
 	for (i = 0; i < entries; i++) {
diff --git a/test-index-version.c b/test-index-version.c
index bfaad9e..f21372a 100644
--- a/test-index-version.c
+++ b/test-index-version.c
@@ -2,7 +2,7 @@
 
 int main(int argc, const char **argv)
 {
-	struct cache_header hdr;
+	struct cache_version_header hdr;
 	int version;
 
 	memset(&hdr,0,sizeof(hdr));
-- 
1.7.10.886.gdf6792c.dirty