Re: [PATCH v6 3/9] ssh signing: retrieve a default key from ssh-agent

if user.signingkey is not set and a ssh signature is requested we call
ssh-add -L and use the first key we get

[snip]

+/* Returns the first public key from an ssh-agent to use for signing */
+static char *get_default_ssh_signing_key(void)
+{
+	struct child_process ssh_add = CHILD_PROCESS_INIT;
+	int ret = -1;
+	struct strbuf key_stdout = STRBUF_INIT;
+	struct strbuf **keys;
+
+	strvec_pushl(&ssh_add.args, "ssh-add", "-L", NULL);
+	ret = pipe_command(&ssh_add, NULL, 0, &key_stdout, 0, NULL, 0);
+	if (!ret) {
+		keys = strbuf_split_max(&key_stdout, '\n', 2);
+		if (keys[0])
+			return strbuf_detach(keys[0], NULL);
+	}
+
+	strbuf_release(&key_stdout);
+	return "";
+}

Could the commit message have a better explanation of why we need this?
(Also, I would think that the command being run needs to be configurable
instead of being just the first "ssh-add" in $PATH, and the parsing of
the output should be more rigorous. But this is moot if we don't need
this feature in the first place.)