[PATCH 3/6] conf: Make conf_tap_fd() operate more like conf_mode()

[David Gibson <david@gibson.dropbear.id.au>]

We have two cases where we need to parse specific options early:
conf_tap_fd() and conf_mode().  conf_tap_fd() has a slightly odd interface,
requiring the caller to use getopt_long() to find the right option, then
pass it in.  Alter it to work like conf_mode() instead, where all the
command line parsing logic is contained within the conf.c function.

This is slightly more lines, but has a clearer division of responsibility.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 conf.c      | 25 +++++++++++++++++++++----
 conf.h      |  2 +-
 isolation.c | 12 ++----------
 3 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/conf.c b/conf.c
index 41c9d557..f0bce41b 100644
--- a/conf.c
+++ b/conf.c
@@ -1153,17 +1153,34 @@ static void conf_sock_listen(const struct ctx *c)
 
 /**
  * conf_tap_fd() - Read tap fd as supplied by -F command line option
- * @arg:	Argument to -F command line option
+ * @argc:	Argument count
+ * @argv:	Command line options
+ *
+ * Return: fd number from --fd option, or -1 if not supplied
  */
-int conf_tap_fd(const char *arg)
+int conf_tap_fd(int argc, char **argv)
 {
-	const char *p = arg;
+	const struct option optfd[] = {	{ "fd", required_argument, NULL, 'F' },
+					{ 0 }, };
+	const char *fdarg = NULL, *p;
 	unsigned long val;
+	int name;
+
+	optind = 0;
+	do {
+		name = getopt_long(argc, argv, "-:F:", optfd, NULL);
+		if (name == 'F')
+			fdarg = optarg;
+	} while (name != -1);
+
+	if (!fdarg)
+		return -1;
 
+	p = fdarg;
 	if (!parse_unsigned(&p, 0, &val) || !parse_eoi(p)	||
 	    val > INT_MAX					||
 	    (val != STDIN_FILENO && val <= STDERR_FILENO))
-		die("Invalid --fd: %s", arg);
+		die("Invalid --fd: %s", fdarg);
 
 	return val;
 }
diff --git a/conf.h b/conf.h
index 1fa1280e..19bf9bc5 100644
--- a/conf.h
+++ b/conf.h
@@ -7,7 +7,7 @@
 #define CONF_H
 
 enum passt_modes conf_mode(int argc, char *argv[]);
-int conf_tap_fd(const char *arg);
+int conf_tap_fd(int argc, char **argv);
 void conf(struct ctx *c, int argc, char **argv);
 void conf_listen_handler(struct ctx *c, uint32_t events);
 void conf_handler(struct ctx *c, uint32_t events);
diff --git a/isolation.c b/isolation.c
index 4bb79e34..c4d476d6 100644
--- a/isolation.c
+++ b/isolation.c
@@ -58,7 +58,6 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <getopt.h>
 #include <grp.h>
 #include <inttypes.h>
 #include <limits.h>
@@ -208,9 +207,7 @@ static int move_root(void)
  */
 int isolate_initial(int argc, char **argv)
 {
-	const struct option optfd[] = { { "fd", required_argument, NULL, 'F' },
-					{ 0 }, };
-	int name, rc, fd_tap = -1;
+	int rc, fd_tap = -1;
 	uint64_t keep;
 
 	/* We want to keep CAP_NET_BIND_SERVICE in the initial
@@ -251,12 +248,7 @@ int isolate_initial(int argc, char **argv)
 
 	drop_caps_ep_except(keep);
 
-	do {
-		name = getopt_long(argc, argv, "-:F:", optfd, NULL);
-
-		if (name == 'F')
-			fd_tap = conf_tap_fd(optarg);
-	} while (name != -1);
+	fd_tap = conf_tap_fd(argc, argv);
 
 	if (fd_tap == -1) {
 		rc = close_range(STDERR_FILENO + 1, ~0U, CLOSE_RANGE_UNSHARE);
-- 
2.55.0