Add support for a "GIT_INDEX_FILE" environment variable.

We use that to specify alternative index files, which can be useful
if you want to (for example) generate a temporary index file to do
some specific operation that you don't want to mess with your main
one with.

It defaults to the regular ".git/index" if it hasn't been specified.

cache.h

@@ -11,6 +11,7 @@
 #include <string.h>
 #include <errno.h>
 #include <sys/mman.h>
+#include <sys/param.h>
 #include <netinet/in.h>
 
 #include <openssl/sha.h>
@@ -84,6 +85,13 @@ unsigned int active_nr, active_alloc;
 #define DB_ENVIRONMENT "SHA1_FILE_DIRECTORY"
 #define DEFAULT_DB_ENVIRONMENT ".git/objects"
 
+#define get_object_directory() (getenv(DB_ENVIRONMENT) ? : DEFAULT_DB_ENVIRONMENT)
+
+#define INDEX_ENVIRONMENT "GIT_INDEX_FILE"
+#define DEFAULT_INDEX_ENVIRONMENT ".git/index"
+
+#define get_index_file() (getenv(INDEX_ENVIRONMENT) ? : DEFAULT_INDEX_ENVIRONMENT)
+
 #define alloc_nr(x) (((x)+16)*3/2)
 
 /* Initialize and use the cache information */

checkout-cache.c

@@ -32,8 +32,6 @@
  * of "-a" causing problems (not possible in the above example,
  * but get used to it in scripting!).
  */
-#include <sys/param.h>
-
 #include "cache.h"
 
 static int force = 0, quiet = 0;

read-cache.c

@@ -188,7 +188,7 @@ int read_cache(void)
 		sha1_file_directory = DEFAULT_DB_ENVIRONMENT;
 	if (access(sha1_file_directory, X_OK) < 0)
 		return error("no access to SHA1 file directory");
-	fd = open(".git/index", O_RDONLY);
+	fd = open(get_index_file(), O_RDONLY);
 	if (fd < 0)
 		return (errno == ENOENT) ? 0 : error("open failed");
 

read-tree.c

@@ -79,12 +79,12 @@ static int read_tree(unsigned char *sha1, const char *base, int baselen)
 	return read_tree_recursive(buffer, "tree", size, base, baselen);
 }
 
-static int remove_lock = 0;
+static char *lockfile_name;
 
 static void remove_lock_file(void)
 {
-	if (remove_lock)
-		unlink(".git/index.lock");
+	if (lockfile_name)
+		unlink(lockfile_name);
 }
 
 static int path_matches(struct cache_entry *a, struct cache_entry *b)
@@ -223,12 +223,16 @@ int main(int argc, char **argv)
 {
 	int i, newfd, merge;
 	unsigned char sha1[20];
+	static char lockfile[MAXPATHLEN+1];
+	const char *indexfile = get_index_file();
 
-	newfd = open(".git/index.lock", O_RDWR | O_CREAT | O_EXCL, 0600);
+	snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
+
+	newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
 	if (newfd < 0)
 		die("unable to create new cachefile");
 	atexit(remove_lock_file);
-	remove_lock = 1;
+	lockfile_name = lockfile;
 
 	merge = 0;
 	for (i = 1; i < argc; i++) {
@@ -268,9 +272,8 @@ int main(int argc, char **argv)
 			die("just how do you expect me to merge %d trees?", stage-1);
 		}
 	}
-	if (write_cache(newfd, active_cache, active_nr) ||
-	    rename(".git/index.lock", ".git/index"))
+	if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
 		die("unable to write new index file");
-	remove_lock = 0;
+	lockfile_name = NULL;
 	return 0;
 }

show-files.c

@@ -6,7 +6,6 @@
  * Copyright (C) Linus Torvalds, 2005
  */
 #include <dirent.h>
-#include <sys/param.h>
 
 #include "cache.h"
 

update-cache.c

@@ -274,25 +274,29 @@ static int add_cacheinfo(char *arg1, char *arg2, char *arg3)
 	return add_cache_entry(ce, allow_add);
 }
 
-static int remove_lock = 0;
+static const char *lockfile_name = NULL;
 
 static void remove_lock_file(void)
 {
-	if (remove_lock)
-		unlink(".git/index.lock");
+	if (lockfile_name)
+		unlink(lockfile_name);
 }
 
 int main(int argc, char **argv)
 {
 	int i, newfd, entries;
 	int allow_options = 1;
+	static char lockfile[MAXPATHLEN+1];
+	const char *indexfile = get_index_file();
 
-	newfd = open(".git/index.lock", O_RDWR | O_CREAT | O_EXCL, 0600);
+	snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
+
+	newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
 	if (newfd < 0)
 		die("unable to create new cachefile");
 
 	atexit(remove_lock_file);
-	remove_lock = 1;
+	lockfile_name = lockfile;
 
 	entries = read_cache();
 	if (entries < 0)
@@ -333,10 +337,9 @@ int main(int argc, char **argv)
 		if (add_file_to_cache(path))
 			die("Unable to add %s to database", path);
 	}
-	if (write_cache(newfd, active_cache, active_nr) ||
-	    rename(".git/index.lock", ".git/index"))
+	if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
 		die("Unable to write new cachefile");
 
-	remove_lock = 0;
+	lockfile_name = NULL;
 	return 0;
 }