[PATCH v3 1/6] conf: Add --dhcp-opt command-line option

[Anshu Kumari <anskuma@redhat.com>]

Introduce the --dhcp-opt flag that allows setting arbitrary DHCP
options from command-line in the form of [Option CODE,VALUE].
This patch adds the option storage in struct ctx and CLI parsing;
the type-aware value parser and DHCP reply injection follow
in subsequent patches.

Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v3:
  - Added dhcp_add_option() helper in dhcp.c for storing options with
    duplicate-code detection.
  - case 33 now calls dhcp_add_option() instead of inline storage.

v2:
  - Added kerneldoc for @custom_opts, @custom_opts.code, @custom_opts.str, and @custom_opts_count in struct ctx
  - Removed len and val[255] fields from struct (moved to patch 3)
  - Removed braces from case 33, moved declarations (optcode, comma, end) to function scope
  - Renamed code → optcode to follow function-scope convention.
---
 conf.c  | 24 +++++++++++++++++++++++-
 dhcp.c  | 38 ++++++++++++++++++++++++++++++++++++++
 dhcp.h  |  1 +
 passt.h | 12 ++++++++++++
 4 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/conf.c b/conf.c
index 029b9c7..ce78af1 100644
--- a/conf.c
+++ b/conf.c
@@ -47,6 +47,7 @@
 #include "lineread.h"
 #include "isolation.h"
 #include "log.h"
+#include "dhcp.h"
 #include "vhost_user.h"
 #include "epoll_ctl.h"
 #include "conf.h"
@@ -616,7 +617,8 @@ static void usage(const char *name, FILE *f, int status)
 		"  -S, --search LIST	Space-separated list, search domains\n"
 		"    a single, empty option disables the DNS search list\n"
 		"  -H, --hostname NAME 	Hostname to configure client with\n"
-		"  --fqdn NAME		FQDN to configure client with\n");
+		"  --fqdn NAME		FQDN to configure client with\n"
+		"  --dhcp-opt CODE,VAL	Set DHCP option by code\n");
 	if (strstr(name, "pasta"))
 		FPRINTF(f, "    default: don't use any search list\n");
 	else
@@ -844,6 +846,10 @@ static void conf_print(const struct ctx *c)
 			info("    router: %s",
 			     inet_ntop(AF_INET, &c->ip4.guest_gw,
 				       buf, sizeof(buf)));
+			for (i = 0; i < c->custom_opts_count; i++)
+				info("    option %u: %s",
+				     c->custom_opts[i].code,
+				     c->custom_opts[i].str);
 		}
 
 		for (i = 0; i < ARRAY_SIZE(c->ip4.dns); i++) {
@@ -1233,6 +1239,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"migrate-no-linger", no_argument,	NULL,		30 },
 		{"stats", required_argument,		NULL,		31 },
 		{"conf-path",	required_argument,	NULL,		'c' },
+		{"dhcp-opt", required_argument,		NULL,		33 },
 		{ 0 },
 	};
 	const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:";
@@ -1248,10 +1255,13 @@ void conf(struct ctx *c, int argc, char **argv)
 	uint8_t prefix_len_from_opt = 0;
 	unsigned int ifi4 = 0, ifi6 = 0;
 	const char *logfile = NULL;
+	unsigned long optcode;
 	char *runas = NULL;
 	size_t logsize = 0;
+	const char *comma;
 	long fd_tap_opt;
 	int name, ret;
+	char *end;
 	uid_t uid;
 	gid_t gid;
 	
@@ -1465,6 +1475,18 @@ void conf(struct ctx *c, int argc, char **argv)
 				die("Can't display statistics if not running in foreground");
 			c->stats = strtol(optarg, NULL, 0);
 			break;
+		case 33:
+			comma = strchr(optarg, ',');
+			if (!comma)
+				die("--dhcp-opt requires CODE,VALUE format");
+
+			optcode = strtoul(optarg, &end, 0);
+			if (end != comma || optcode < 1 || optcode > 254)
+				die("DHCP option code must be 1-254: %s",
+				    optarg);
+
+			dhcp_add_option(c, optcode, comma + 1);
+			break;
 		case 'd':
 			c->debug = 1;
 			c->quiet = 0;
diff --git a/dhcp.c b/dhcp.c
index 1ff8cba..c5fbf37 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -33,6 +33,44 @@
 #include "log.h"
 #include "dhcp.h"
 
+
+/**
+ * dhcp_add_option() - Add or update a custom DHCP option
+ * @c:		Execution context
+ * @code:	DHCP option code
+ * @val_str:	Value string from command line
+ *
+ * If @code was already added, the previous value is overwritten.
+ * Calls die() on any error.
+ *
+ * Return: 0 on success
+ */
+int dhcp_add_option(struct ctx *c, uint8_t code, const char *val_str)
+{
+	int idx;
+
+	for (idx = 0; idx < c->custom_opts_count; idx++) {
+		if (c->custom_opts[idx].code == code)
+			break;
+	}
+
+	if (idx == c->custom_opts_count) {
+		if (c->custom_opts_count >= MAX_CUSTOM_DHCP_OPTS)
+			die("Too many --dhcp-opt entries (max %d)",
+			    MAX_CUSTOM_DHCP_OPTS);
+		c->custom_opts_count++;
+	}
+
+	c->custom_opts[idx].code = code;
+
+	if (snprintf_check(c->custom_opts[idx].str,
+			   sizeof(c->custom_opts[0].str),
+			   "%s", val_str))
+		die("DHCP option value too long: %s", val_str);
+
+	return 0;
+}
+
 /**
  * struct opt - DHCP option
  * @sent:	Convenience flag, set while filling replies
diff --git a/dhcp.h b/dhcp.h
index cd50c99..9c8f1e3 100644
--- a/dhcp.h
+++ b/dhcp.h
@@ -8,5 +8,6 @@
 
 int dhcp(const struct ctx *c, struct iov_tail *data);
 void dhcp_init(void);
+int dhcp_add_option(struct ctx *c, uint8_t code, const char *val_str);
 
 #endif /* DHCP_H */
diff --git a/passt.h b/passt.h
index 1726965..3a0816f 100644
--- a/passt.h
+++ b/passt.h
@@ -182,6 +182,10 @@ struct ip6_ctx {
  * @dns_search:		DNS search list
  * @hostname:		Guest hostname
  * @fqdn:		Guest FQDN
+ * @custom_opts:	User-specified DHCP options from --dhcp-opt
+ * @custom_opts.code:	DHCP option code
+ * @custom_opts.str:	Original string value from command line
+ * @custom_opts_count:	Number of entries in @custom_opts
  * @ifi6:		Template interface for IPv6, -1: none, 0: IPv6 disabled
  * @ip6:		IPv6 configuration
  * @pasta_ifn:		Name of namespace interface for pasta
@@ -263,6 +267,14 @@ struct ctx {
 	char hostname[PASST_MAXDNAME];
 	char fqdn[PASST_MAXDNAME];
 
+#define MAX_CUSTOM_DHCP_OPTS	32
+
+	struct {
+		uint8_t code;
+		char str[256];
+	} custom_opts[MAX_CUSTOM_DHCP_OPTS];
+	int custom_opts_count;
+
 	int ifi6;
 	struct ip6_ctx ip6;
 
-- 
2.54.0