[PATCH v4 5/5] read-cache: clean up casting and byte decoding

[Ben Peart <benpeart@microsoft.com>]

This patch does a clean up pass to minimize the casting required to work
with the memory mapped index (mmap).

It also makes the decoding of network byte order more consistent by using
get_be32() where possible.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
---
 read-cache.c | 49 +++++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 26 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index d21ccb5e67..6220abc491 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1655,7 +1655,7 @@ int verify_index_checksum;
 /* Allow fsck to force verification of the cache entry order. */
 int verify_ce_order;
 
-static int verify_hdr(struct cache_header *hdr, unsigned long size)
+static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 {
 	git_hash_ctx c;
 	unsigned char hash[GIT_MAX_RAWSZ];
@@ -1679,7 +1679,7 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)
 }
 
 static int read_index_extension(struct index_state *istate,
-				const char *ext, void *data, unsigned long sz)
+				const char *ext, const char *data, unsigned long sz)
 {
 	switch (CACHE_EXT(ext)) {
 	case CACHE_EXT_TREE:
@@ -1906,7 +1906,7 @@ static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
 }
 
 #ifndef NO_PTHREADS
-static unsigned long read_eoie_extension(void *mmap_, size_t mmap_size);
+static unsigned long read_eoie_extension(const char *mmap, size_t mmap_size);
 #endif
 static void write_eoie_extension(struct strbuf *sb, git_hash_ctx *eoie_context, unsigned long offset);
 
@@ -1916,14 +1916,14 @@ struct load_index_extensions
 	pthread_t pthread;
 #endif
 	struct index_state *istate;
-	void *mmap;
+	const char *mmap;
 	size_t mmap_size;
 	unsigned long src_offset;
 };
 
-static void *load_index_extensions(void *_data)
+static void *load_index_extensions(void *data)
 {
-	struct load_index_extensions *p = _data;
+	struct load_index_extensions *p = data;
 	unsigned long src_offset = p->src_offset;
 
 	while (src_offset <= p->mmap_size - the_hash_algo->rawsz - 8) {
@@ -1934,13 +1934,12 @@ static void *load_index_extensions(void *_data)
 		 * in 4-byte network byte order.
 		 */
 		uint32_t extsize;
-		memcpy(&extsize, (char *)p->mmap + src_offset + 4, 4);
-		extsize = ntohl(extsize);
+		extsize = get_be32(p->mmap + src_offset + 4);
 		if (read_index_extension(p->istate,
-			(const char *)p->mmap + src_offset,
-			(char *)p->mmap + src_offset + 8,
+			p->mmap + src_offset,
+			p->mmap + src_offset + 8,
 			extsize) < 0) {
-			munmap(p->mmap, p->mmap_size);
+			munmap((void *)p->mmap, p->mmap_size);
 			die("index file corrupt");
 		}
 		src_offset += 8;
@@ -1955,7 +1954,7 @@ static void *load_index_extensions(void *_data)
  * from the memory mapped file and add them to the given index.
  */
 static unsigned long load_cache_entry_block(struct index_state *istate,
-			struct mem_pool *ce_mem_pool, int offset, int nr, void *mmap,
+			struct mem_pool *ce_mem_pool, int offset, int nr, const char *mmap,
 			unsigned long start_offset, const struct cache_entry *previous_ce)
 {
 	int i;
@@ -1966,7 +1965,7 @@ static unsigned long load_cache_entry_block(struct index_state *istate,
 		struct cache_entry *ce;
 		unsigned long consumed;
 
-		disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
+		disk_ce = (struct ondisk_cache_entry *)(mmap + src_offset);
 		ce = create_from_disk(ce_mem_pool, istate->version, disk_ce, &consumed, previous_ce);
 		set_index_entry(istate, i, ce);
 
@@ -1977,7 +1976,7 @@ static unsigned long load_cache_entry_block(struct index_state *istate,
 }
 
 static unsigned long load_all_cache_entries(struct index_state *istate,
-			void *mmap, size_t mmap_size, unsigned long src_offset)
+			const char *mmap, size_t mmap_size, unsigned long src_offset)
 {
 	unsigned long consumed;
 
@@ -2008,7 +2007,7 @@ struct load_cache_entries_thread_data
 	struct index_state *istate;
 	struct mem_pool *ce_mem_pool;
 	int offset, nr;
-	void *mmap;
+	const char *mmap;
 	unsigned long start_offset;
 	struct cache_entry *previous_ce;
 	unsigned long consumed;	/* return # of bytes in index file processed */
@@ -2028,7 +2027,7 @@ static void *load_cache_entries_thread(void *_data)
 }
 
 static unsigned long load_cache_entries_threaded(int nr_threads, struct index_state *istate,
-			void *mmap, size_t mmap_size, unsigned long src_offset)
+			const char *mmap, size_t mmap_size, unsigned long src_offset)
 {
 	struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
 	struct load_cache_entries_thread_data *data;
@@ -2097,7 +2096,7 @@ static unsigned long load_cache_entries_threaded(int nr_threads, struct index_st
 				break;
 		}
 
-		ondisk = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
+		ondisk = (struct ondisk_cache_entry *)(mmap + src_offset);
 
 		/* On-disk flags are just 16 bits */
 		flags = get_be16(&ondisk->flags);
@@ -2145,8 +2144,8 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	int fd;
 	struct stat st;
 	unsigned long src_offset;
-	struct cache_header *hdr;
-	void *mmap;
+	const struct cache_header *hdr;
+	const char *mmap;
 	size_t mmap_size;
 	struct load_index_extensions p = { 0 };
 	unsigned long extension_offset = 0;
@@ -2178,7 +2177,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		die_errno("unable to map index file");
 	close(fd);
 
-	hdr = mmap;
+	hdr = (const struct cache_header *)mmap;
 	if (verify_hdr(hdr, mmap_size) < 0)
 		goto unmap;
 
@@ -2238,11 +2237,11 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		p.src_offset = src_offset;
 		load_index_extensions(&p);
 	}
-	munmap(mmap, mmap_size);
+	munmap((void *)mmap, mmap_size);
 	return istate->cache_nr;
 
 unmap:
-	munmap(mmap, mmap_size);
+	munmap((void *)mmap, mmap_size);
 	die("index file corrupt");
 }
 
@@ -3265,7 +3264,7 @@ int should_validate_cache_entries(void)
 #define EOIE_SIZE_WITH_HEADER (4 + 4 + EOIE_SIZE) /* <4-byte signature> + <4-byte length> + EOIE_SIZE */
 
 #ifndef NO_PTHREADS
-static unsigned long read_eoie_extension(void *mmap_, size_t mmap_size)
+static unsigned long read_eoie_extension(const char *mmap, size_t mmap_size)
 {
 	/*
 	 * The end of index entries (EOIE) extension is guaranteed to be last
@@ -3276,7 +3275,6 @@ static unsigned long read_eoie_extension(void *mmap_, size_t mmap_size)
 	 * <4-byte offset>
 	 * <20-byte hash>
 	 */
-	const char *mmap = mmap_;
 	const char *index, *eoie;
 	uint32_t extsize;
 	unsigned long offset, src_offset;
@@ -3329,8 +3327,7 @@ static unsigned long read_eoie_extension(void *mmap_, size_t mmap_size)
 		 * in 4-byte network byte order.
 		 */
 		uint32_t extsize;
-		memcpy(&extsize, (char *)mmap + src_offset + 4, 4);
-		extsize = ntohl(extsize);
+		extsize = get_be32(mmap + src_offset + 4);
 
 		/* verify the extension size isn't so large it will wrap around */
 		if (src_offset + 8 + extsize < src_offset)
-- 
2.18.0.windows.1