convert: update generic functions to only use generic data structures

Update all functions that are going to be moved into a reusable module
so that they only work with the reusable data structures.  Move code
that is specific to the filter out into the filter specific functions.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

convert.c

@@ -556,7 +556,6 @@ static void kill_multi_file_filter(struct hashmap *hashmap, struct subprocess_en
 	finish_command(&entry->process);
 
 	hashmap_remove(hashmap, entry, NULL);
-	free(entry);
 }
 
 static void stop_multi_file_filter(struct child_process *process)
@@ -570,14 +569,15 @@ static void stop_multi_file_filter(struct child_process *process)
 	finish_command(process);
 }
 
-static int start_multi_file_filter_fn(struct cmd2process *entry)
+static int start_multi_file_filter_fn(struct subprocess_entry *subprocess)
 {
 	int err;
+	struct cmd2process *entry = (struct cmd2process *)subprocess;
 	struct string_list cap_list = STRING_LIST_INIT_NODUP;
 	char *cap_buf;
 	const char *cap_name;
-	struct child_process *process = &entry->subprocess.process;
-	const char *cmd = entry->subprocess.cmd;
+	struct child_process *process = &subprocess->process;
+	const char *cmd = subprocess->cmd;
 
 	sigchain_push(SIGPIPE, SIG_IGN);
 
@@ -629,17 +629,16 @@ done:
 	return err;
 }
 
-static struct cmd2process *start_multi_file_filter(struct hashmap *hashmap, const char *cmd)
+typedef int(*subprocess_start_fn)(struct subprocess_entry *entry);
+int start_multi_file_filter(struct hashmap *hashmap, struct subprocess_entry *entry, const char *cmd,
+	subprocess_start_fn startfn)
 {
 	int err;
-	struct cmd2process *entry;
 	struct child_process *process;
 	const char *argv[] = { cmd, NULL };
 
-	entry = xmalloc(sizeof(*entry));
-	entry->subprocess.cmd = cmd;
-	entry->supported_capabilities = 0;
-	process = &entry->subprocess.process;
+	entry->cmd = cmd;
+	process = &entry->process;
 
 	child_process_init(process);
 	process->argv = argv;
@@ -649,22 +648,23 @@ static struct cmd2process *start_multi_file_filter(struct hashmap *hashmap, cons
 	process->clean_on_exit = 1;
 	process->clean_on_exit_handler = stop_multi_file_filter;
 
-	if (start_command(process)) {
+	err = start_command(process);
+	if (err) {
 		error("cannot fork to run external filter '%s'", cmd);
-		return NULL;
+		return err;
 	}
 
 	hashmap_entry_init(entry, strhash(cmd));
 
-	err = start_multi_file_filter_fn(entry);
+	err = startfn(entry);
 	if (err) {
 		error("initialization for external filter '%s' failed", cmd);
-		kill_multi_file_filter(hashmap, &entry->subprocess);
-		return NULL;
+		kill_multi_file_filter(hashmap, entry);
+		return err;
 	}
 
 	hashmap_add(hashmap, entry);
-	return entry;
+	return 0;
 }
 
 static int apply_multi_file_filter(const char *path, const char *src, size_t len,
@@ -689,9 +689,13 @@ static int apply_multi_file_filter(const char *path, const char *src, size_t len
 	fflush(NULL);
 
 	if (!entry) {
-		entry = start_multi_file_filter(&cmd_process_map, cmd);
-		if (!entry)
+		entry = xmalloc(sizeof(*entry));
+		entry->supported_capabilities = 0;
+
+		if (start_multi_file_filter(&cmd_process_map, &entry->subprocess, cmd, start_multi_file_filter_fn)) {
+			free(entry);
 			return 0;
+		}
 	}
 	process = &entry->subprocess.process;
 
@@ -765,6 +769,7 @@ done:
 			 */
 			error("external filter '%s' failed", cmd);
 			kill_multi_file_filter(&cmd_process_map, &entry->subprocess);
+			free(entry);
 		}
 	} else {
 		strbuf_swap(dst, &nbuf);