db: Allow override arch when using --root

This is so we can do x86 --root installs on x86_64 hosts.

Using --arch without --root can make great damage so we only enable it
if --root is used.

src/apk.c

@@ -66,6 +66,8 @@ static struct apk_option generic_options[] = {
 				required_argument, "REPOFILE" },
 	{ 0x109, "no-network",	"Do not use network (cache is still used)" },
 	{ 0x111, "overlay-from-stdin", "Read list of overlay files from stdin" },
+	{ 0x112, "arch", 	"Use architecture with --root",
+				required_argument, "ARCH" },
 };
 
 static int version(void)
@@ -369,6 +371,9 @@ int main(int argc, char **argv)
 		case 0x111:
 			apk_flags |= APK_OVERLAY_FROM_STDIN;
 			break;
+		case 0x112:
+			dbopts.arch = optarg;
+			break;
 		default:
 			if (applet == NULL || applet->parse == NULL ||
 			    applet->parse(ctx, &dbopts, r,

src/apk_database.h

@@ -95,6 +95,7 @@ struct apk_db_options {
 	int lock_wait;
 	unsigned long open_flags;
 	char *root;
+	char *arch;
 	char *keys_dir;
 	char *repositories_file;
 	struct list_head repository_list;

src/database.c

@@ -49,7 +49,6 @@ enum {
 
 int apk_verbosity = 1;
 unsigned int apk_flags = 0;
-const char *apk_arch = APK_DEFAULT_ARCH;
 
 const char * const apkindex_tar_gz = "APKINDEX.tar.gz";
 static const char * const apk_static_cache_dir = "var/cache/apk";
@@ -1149,6 +1148,11 @@ int apk_db_open(struct apk_database *db, struct apk_db_options *dbopts)
 	apk_string_array_init(&db->protected_paths);
 	db->permanent = 1;
 
+	if (dbopts->root && dbopts->arch) {
+		db->arch = apk_blob_atomize(APK_BLOB_STR(dbopts->arch));
+	} else {
+		db->arch = apk_blob_atomize(APK_BLOB_STR(APK_DEFAULT_ARCH));
+	}
 	db->root = strdup(dbopts->root ?: "/");
 	db->root_fd = openat(AT_FDCWD, db->root, O_RDONLY | O_CLOEXEC);
 	if (db->root_fd < 0 && (dbopts->open_flags & APK_OPENF_CREATE)) {
@@ -1226,7 +1230,6 @@ int apk_db_open(struct apk_database *db, struct apk_db_options *dbopts)
 		db->cachetmp_fd = db->cache_fd;
 	}
 
-	db->arch = apk_blob_atomize(APK_BLOB_STR(apk_arch));
 	db->keys_fd = openat(db->root_fd,
 			     dbopts->keys_dir ?: "etc/apk/keys",
 			     O_RDONLY | O_CLOEXEC);