[PATCH v3 0/3] dhcp: Add support for Rapid Commit, broadcast replies

[PATCH v3 0/3] dhcp: Add support for Rapid Commit, broadcast replies

[Stefano Brivio]

These are all changes coming from pending muvm experiments where I'm
trying to speed up and simplify the networking setup in the guest.

v3: In 1/3, set 'slen' for options we won't send to -1 in dhcp_init(),
    and reset it for option 80 every time we handle a DHCP request. Add
    a comment about DHCP needing a valid message type (option 53)

v2: In 3/3, add in4addr_broadcast to ip.h, instead of open-coding it in
    dhcp()

Stefano Brivio (3):
  dhcp: Use -1 as "missing option" length instead of 0
  dhcp: Introduce support for Rapid Commit (option 80, RFC 4039)
  dhcp: Honour broadcast flag (RFC 2131, 4.1)

 dhcp.c | 51 ++++++++++++++++++++++++++++++++++++++++-----------
 ip.h   |  3 +++
 2 files changed, 43 insertions(+), 11 deletions(-)

-- 
2.43.0

[PATCH v3 1/3] dhcp: Use -1 as "missing option" length instead of 0

[Stefano Brivio]

We want to add support for option 80 (Rapid Commit, RFC 4039), whose
length is 0.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 dhcp.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/dhcp.c b/dhcp.c
index a06f143..57f69a5 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -36,9 +36,9 @@
 /**
  * struct opt - DHCP option
  * @sent:	Convenience flag, set while filling replies
- * @slen:	Length of option defined for server
+ * @slen:	Length of option defined for server, -1 if not going to be sent
  * @s:		Option payload from server
- * @clen:	Length of option received from client
+ * @clen:	Length of option received from client, -1 if not received
  * @c:		Option payload from client
  */
 struct opt {
@@ -68,6 +68,11 @@ static struct opt opts[255];
  */
 void dhcp_init(void)
 {
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(opts); i++)
+		opts[i].slen = -1;
+
 	opts[1]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Mask */
 	opts[3]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Router */
 	opts[51] = (struct opt) { 0, 4, {  0xff,
@@ -154,17 +159,17 @@ static int fill(struct msg *m)
 	 * option 53 at the beginning of the list.
 	 * Put it there explicitly, unless requested via option 55.
 	 */
-	if (!memchr(opts[55].c, 53, opts[55].clen))
+	if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen))
 		fill_one(m, 53, &offset);
 
 	for (i = 0; i < opts[55].clen; i++) {
 		o = opts[55].c[i];
-		if (opts[o].slen)
+		if (opts[o].slen != -1)
 			fill_one(m, o, &offset);
 	}
 
 	for (o = 0; o < 255; o++) {
-		if (opts[o].slen && !opts[o].sent)
+		if (opts[o].slen != -1 && !opts[o].sent)
 			fill_one(m, o, &offset);
 	}
 
@@ -264,6 +269,9 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
 						 ".\xc0");
 		}
 	}
+
+	if (!opts[119].slen)
+		opts[119].slen = -1;
 }
 
 /**
@@ -313,6 +321,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
 
 	offset += offsetof(struct msg, o);
 
+	for (i = 0; i < ARRAY_SIZE(opts); i++)
+		opts[i].clen = -1;
+
 	while (opt_off + 2 < opt_len) {
 		const uint8_t *olen, *val;
 		uint8_t *type;
@@ -334,8 +345,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
 	if (opts[53].c[0] == DHCPDISCOVER) {
 		info("DHCP: offer to discover");
 		opts[53].s[0] = DHCPOFFER;
-	} else if (opts[53].c[0] == DHCPREQUEST || !opts[53].clen) {
-		info("%s: ack to request", opts[53].clen ? "DHCP" : "BOOTP");
+	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
+		info("%s: ack to request", /* DHCP needs a valid message type */
+		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");
 		opts[53].s[0] = DHCPACK;
 	} else {
 		return -1;
@@ -374,6 +386,8 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		((struct in_addr *)opts[6].s)[i] = c->ip4.dns[i];
 		opts[6].slen += sizeof(uint32_t);
 	}
+	if (!opts[6].slen)
+		opts[6].slen = -1;
 
 	if (!c->no_dhcp_dns_search)
 		opt_set_dns_search(c, sizeof(m->o));
-- 
@@ -36,9 +36,9 @@
 /**
  * struct opt - DHCP option
  * @sent:	Convenience flag, set while filling replies
- * @slen:	Length of option defined for server
+ * @slen:	Length of option defined for server, -1 if not going to be sent
  * @s:		Option payload from server
- * @clen:	Length of option received from client
+ * @clen:	Length of option received from client, -1 if not received
  * @c:		Option payload from client
  */
 struct opt {
@@ -68,6 +68,11 @@ static struct opt opts[255];
  */
 void dhcp_init(void)
 {
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(opts); i++)
+		opts[i].slen = -1;
+
 	opts[1]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Mask */
 	opts[3]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Router */
 	opts[51] = (struct opt) { 0, 4, {  0xff,
@@ -154,17 +159,17 @@ static int fill(struct msg *m)
 	 * option 53 at the beginning of the list.
 	 * Put it there explicitly, unless requested via option 55.
 	 */
-	if (!memchr(opts[55].c, 53, opts[55].clen))
+	if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen))
 		fill_one(m, 53, &offset);
 
 	for (i = 0; i < opts[55].clen; i++) {
 		o = opts[55].c[i];
-		if (opts[o].slen)
+		if (opts[o].slen != -1)
 			fill_one(m, o, &offset);
 	}
 
 	for (o = 0; o < 255; o++) {
-		if (opts[o].slen && !opts[o].sent)
+		if (opts[o].slen != -1 && !opts[o].sent)
 			fill_one(m, o, &offset);
 	}
 
@@ -264,6 +269,9 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
 						 ".\xc0");
 		}
 	}
+
+	if (!opts[119].slen)
+		opts[119].slen = -1;
 }
 
 /**
@@ -313,6 +321,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
 
 	offset += offsetof(struct msg, o);
 
+	for (i = 0; i < ARRAY_SIZE(opts); i++)
+		opts[i].clen = -1;
+
 	while (opt_off + 2 < opt_len) {
 		const uint8_t *olen, *val;
 		uint8_t *type;
@@ -334,8 +345,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
 	if (opts[53].c[0] == DHCPDISCOVER) {
 		info("DHCP: offer to discover");
 		opts[53].s[0] = DHCPOFFER;
-	} else if (opts[53].c[0] == DHCPREQUEST || !opts[53].clen) {
-		info("%s: ack to request", opts[53].clen ? "DHCP" : "BOOTP");
+	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
+		info("%s: ack to request", /* DHCP needs a valid message type */
+		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");
 		opts[53].s[0] = DHCPACK;
 	} else {
 		return -1;
@@ -374,6 +386,8 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		((struct in_addr *)opts[6].s)[i] = c->ip4.dns[i];
 		opts[6].slen += sizeof(uint32_t);
 	}
+	if (!opts[6].slen)
+		opts[6].slen = -1;
 
 	if (!c->no_dhcp_dns_search)
 		opt_set_dns_search(c, sizeof(m->o));
-- 
2.43.0

Re: [PATCH v3 1/3] dhcp: Use -1 as "missing option" length instead of 0

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 3568 bytes --]

On Mon, Nov 25, 2024 at 04:28:10PM +0100, Stefano Brivio wrote:
> We want to add support for option 80 (Rapid Commit, RFC 4039), whose
> length is 0.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbera.id.u>

> ---
>  dhcp.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index a06f143..57f69a5 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -36,9 +36,9 @@
>  /**
>   * struct opt - DHCP option
>   * @sent:	Convenience flag, set while filling replies
> - * @slen:	Length of option defined for server
> + * @slen:	Length of option defined for server, -1 if not going to be sent
>   * @s:		Option payload from server
> - * @clen:	Length of option received from client
> + * @clen:	Length of option received from client, -1 if not received
>   * @c:		Option payload from client
>   */
>  struct opt {
> @@ -68,6 +68,11 @@ static struct opt opts[255];
>   */
>  void dhcp_init(void)
>  {
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(opts); i++)
> +		opts[i].slen = -1;
> +
>  	opts[1]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Mask */
>  	opts[3]  = (struct opt) { 0, 4, {     0 }, 0, { 0 }, };	/* Router */
>  	opts[51] = (struct opt) { 0, 4, {  0xff,
> @@ -154,17 +159,17 @@ static int fill(struct msg *m)
>  	 * option 53 at the beginning of the list.
>  	 * Put it there explicitly, unless requested via option 55.
>  	 */
> -	if (!memchr(opts[55].c, 53, opts[55].clen))
> +	if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen))
>  		fill_one(m, 53, &offset);
>  
>  	for (i = 0; i < opts[55].clen; i++) {
>  		o = opts[55].c[i];
> -		if (opts[o].slen)
> +		if (opts[o].slen != -1)
>  			fill_one(m, o, &offset);
>  	}
>  
>  	for (o = 0; o < 255; o++) {
> -		if (opts[o].slen && !opts[o].sent)
> +		if (opts[o].slen != -1 && !opts[o].sent)
>  			fill_one(m, o, &offset);
>  	}
>  
> @@ -264,6 +269,9 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
>  						 ".\xc0");
>  		}
>  	}
> +
> +	if (!opts[119].slen)
> +		opts[119].slen = -1;
>  }
>  
>  /**
> @@ -313,6 +321,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  
>  	offset += offsetof(struct msg, o);
>  
> +	for (i = 0; i < ARRAY_SIZE(opts); i++)
> +		opts[i].clen = -1;
> +
>  	while (opt_off + 2 < opt_len) {
>  		const uint8_t *olen, *val;
>  		uint8_t *type;
> @@ -334,8 +345,9 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  	if (opts[53].c[0] == DHCPDISCOVER) {
>  		info("DHCP: offer to discover");
>  		opts[53].s[0] = DHCPOFFER;
> -	} else if (opts[53].c[0] == DHCPREQUEST || !opts[53].clen) {
> -		info("%s: ack to request", opts[53].clen ? "DHCP" : "BOOTP");
> +	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
> +		info("%s: ack to request", /* DHCP needs a valid message type */
> +		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");
>  		opts[53].s[0] = DHCPACK;
>  	} else {
>  		return -1;
> @@ -374,6 +386,8 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  		((struct in_addr *)opts[6].s)[i] = c->ip4.dns[i];
>  		opts[6].slen += sizeof(uint32_t);
>  	}
> +	if (!opts[6].slen)
> +		opts[6].slen = -1;
>  
>  	if (!c->no_dhcp_dns_search)
>  		opt_set_dns_search(c, sizeof(m->o));

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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[PATCH v3 2/3] dhcp: Introduce support for Rapid Commit (option 80, RFC 4039)

[Stefano Brivio]

I'm trying to speed up and simplify IP address acquisition in muvm.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 dhcp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/dhcp.c b/dhcp.c
index 57f69a5..90bb534 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -342,9 +342,16 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		opt_off += *olen + 2;
 	}
 
+	opts[80].slen = -1;
 	if (opts[53].c[0] == DHCPDISCOVER) {
-		info("DHCP: offer to discover");
-		opts[53].s[0] = DHCPOFFER;
+		if (opts[80].clen == -1) {
+			info("DHCP: offer to discover");
+			opts[53].s[0] = DHCPOFFER;
+		} else {
+			info("DHCP: ack to discover (Rapid Commit)");
+			opts[53].s[0] = DHCPACK;
+			opts[80].slen = 0;
+		}
 	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
 		info("%s: ack to request", /* DHCP needs a valid message type */
 		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");
-- 
@@ -342,9 +342,16 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		opt_off += *olen + 2;
 	}
 
+	opts[80].slen = -1;
 	if (opts[53].c[0] == DHCPDISCOVER) {
-		info("DHCP: offer to discover");
-		opts[53].s[0] = DHCPOFFER;
+		if (opts[80].clen == -1) {
+			info("DHCP: offer to discover");
+			opts[53].s[0] = DHCPOFFER;
+		} else {
+			info("DHCP: ack to discover (Rapid Commit)");
+			opts[53].s[0] = DHCPACK;
+			opts[80].slen = 0;
+		}
 	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
 		info("%s: ack to request", /* DHCP needs a valid message type */
 		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");
-- 
2.43.0

Re: [PATCH v3 2/3] dhcp: Introduce support for Rapid Commit (option 80, RFC 4039)

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 1331 bytes --]

On Mon, Nov 25, 2024 at 04:28:11PM +0100, Stefano Brivio wrote:
> I'm trying to speed up and simplify IP address acquisition in muvm.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  dhcp.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index 57f69a5..90bb534 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -342,9 +342,16 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  		opt_off += *olen + 2;
>  	}
>  
> +	opts[80].slen = -1;
>  	if (opts[53].c[0] == DHCPDISCOVER) {
> -		info("DHCP: offer to discover");
> -		opts[53].s[0] = DHCPOFFER;
> +		if (opts[80].clen == -1) {
> +			info("DHCP: offer to discover");
> +			opts[53].s[0] = DHCPOFFER;
> +		} else {
> +			info("DHCP: ack to discover (Rapid Commit)");
> +			opts[53].s[0] = DHCPACK;
> +			opts[80].slen = 0;
> +		}
>  	} else if (opts[53].c[0] == DHCPREQUEST || opts[53].clen <= 0) {
>  		info("%s: ack to request", /* DHCP needs a valid message type */
>  		     (opts[53].clen <= 0) ? "DHCP" : "BOOTP");

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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[PATCH v3 3/3] dhcp: Honour broadcast flag (RFC 2131, 4.1)

[Stefano Brivio]

It's widely considered a legacy option nowadays, and I've haven't seen
clients setting it since Windows 95, but it's convenient for a minimal
DHCP client not using raw IP sockets such as what I'm playing with for
muvm.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 dhcp.c | 12 ++++++++++--
 ip.h   |  3 +++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/dhcp.c b/dhcp.c
index 90bb534..b3688ef 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -112,6 +112,8 @@ struct msg {
 	uint32_t xid;
 	uint16_t secs;
 	uint16_t flags;
+#define FLAG_BROADCAST	htons_constant(0x8000)
+
 	uint32_t ciaddr;
 	struct in_addr yiaddr;
 	uint32_t siaddr;
@@ -285,10 +287,10 @@ int dhcp(const struct ctx *c, const struct pool *p)
 {
 	size_t mlen, dlen, offset = 0, opt_len, opt_off = 0;
 	char macstr[ETH_ADDRSTRLEN];
+	struct in_addr mask, dst;
 	const struct ethhdr *eh;
 	const struct iphdr *iph;
 	const struct udphdr *uh;
-	struct in_addr mask;
 	unsigned int i;
 	struct msg *m;
 
@@ -400,7 +402,13 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		opt_set_dns_search(c, sizeof(m->o));
 
 	dlen = offsetof(struct msg, o) + fill(m);
-	tap_udp4_send(c, c->ip4.our_tap_addr, 67, c->ip4.addr, 68, m, dlen);
+
+	if (m->flags & FLAG_BROADCAST)
+		dst = in4addr_broadcast;
+	else
+		dst = c->ip4.addr;
+
+	tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, m, dlen);
 
 	return 1;
 }
diff --git a/ip.h b/ip.h
index 0742612..1544dbf 100644
--- a/ip.h
+++ b/ip.h
@@ -101,4 +101,7 @@ static const struct in6_addr in6addr_ll_all_nodes = {
 	},
 };
 
+/* IPv4 Limited Broadcast (RFC 919, Section 7), 255.255.255.255 */
+static const struct in_addr in4addr_broadcast = { 0xffffffff };
+
 #endif /* IP_H */
-- 
@@ -101,4 +101,7 @@ static const struct in6_addr in6addr_ll_all_nodes = {
 	},
 };
 
+/* IPv4 Limited Broadcast (RFC 919, Section 7), 255.255.255.255 */
+static const struct in_addr in4addr_broadcast = { 0xffffffff };
+
 #endif /* IP_H */
-- 
2.43.0

Re: [PATCH v3 3/3] dhcp: Honour broadcast flag (RFC 2131, 4.1)

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 2216 bytes --]

On Mon, Nov 25, 2024 at 04:28:12PM +0100, Stefano Brivio wrote:
> It's widely considered a legacy option nowadays, and I've haven't seen
> clients setting it since Windows 95, but it's convenient for a minimal
> DHCP client not using raw IP sockets such as what I'm playing with for
> muvm.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  dhcp.c | 12 ++++++++++--
>  ip.h   |  3 +++
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index 90bb534..b3688ef 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -112,6 +112,8 @@ struct msg {
>  	uint32_t xid;
>  	uint16_t secs;
>  	uint16_t flags;
> +#define FLAG_BROADCAST	htons_constant(0x8000)
> +
>  	uint32_t ciaddr;
>  	struct in_addr yiaddr;
>  	uint32_t siaddr;
> @@ -285,10 +287,10 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  {
>  	size_t mlen, dlen, offset = 0, opt_len, opt_off = 0;
>  	char macstr[ETH_ADDRSTRLEN];
> +	struct in_addr mask, dst;
>  	const struct ethhdr *eh;
>  	const struct iphdr *iph;
>  	const struct udphdr *uh;
> -	struct in_addr mask;
>  	unsigned int i;
>  	struct msg *m;
>  
> @@ -400,7 +402,13 @@ int dhcp(const struct ctx *c, const struct pool *p)
>  		opt_set_dns_search(c, sizeof(m->o));
>  
>  	dlen = offsetof(struct msg, o) + fill(m);
> -	tap_udp4_send(c, c->ip4.our_tap_addr, 67, c->ip4.addr, 68, m, dlen);
> +
> +	if (m->flags & FLAG_BROADCAST)
> +		dst = in4addr_broadcast;
> +	else
> +		dst = c->ip4.addr;
> +
> +	tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, m, dlen);
>  
>  	return 1;
>  }
> diff --git a/ip.h b/ip.h
> index 0742612..1544dbf 100644
> --- a/ip.h
> +++ b/ip.h
> @@ -101,4 +101,7 @@ static const struct in6_addr in6addr_ll_all_nodes = {
>  	},
>  };
>  
> +/* IPv4 Limited Broadcast (RFC 919, Section 7), 255.255.255.255 */
> +static const struct in_addr in4addr_broadcast = { 0xffffffff };
> +
>  #endif /* IP_H */

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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