On the command line -m 0 means "don't assign an MTU" (letting the guest
use
its default. However, internally we use (c->mtu == -1) to represent that
state. We use (c->mtu == 0) to represent "the user didn't specify on the
command line, so use the default" - but this is only used during conf(),
never afterwards.
This is unnecessarily confusing. We can instead just initialise c->mtu to
its default (65520) before parsing options and use 0 on both the command
line and internally to represent the "don't assign" special case. This
ensures that c->mtu is always 0..65535, so we can store it in a uint16_t
which is more natural.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 11 ++---------
dhcp.c | 2 +-
ndp.c | 2 +-
passt.h | 3 ++-
pasta.c | 2 +-
tcp.c | 2 +-
6 files changed, 8 insertions(+), 14 deletions(-)
diff --git a/conf.c b/conf.c
index 335f37c9..c5ee07b0 100644
--- a/conf.c
+++ b/conf.c
@@ -1413,6 +1413,7 @@ void conf(struct ctx *c, int argc, char **argv)
optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:";
}
+ c->mtu = ROUND_DOWN(ETH_MAX_MTU - ETH_HLEN, sizeof(uint32_t));
c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET;
c->udp.fwd_in.mode = c->udp.fwd_out.mode = FWD_UNSET;
memcpy(c->our_tap_mac, MAC_OUR_LAA, ETH_ALEN);
@@ -1662,12 +1663,7 @@ void conf(struct ctx *c, int argc, char **argv)
if (errno || *e)
die("Invalid MTU: %s", optarg);
- if (!mtu) {
- c->mtu = -1;
- break;
- }
-
- if (mtu < ETH_MIN_MTU || mtu > ETH_MAX_MTU) {
+ if (mtu && (mtu < ETH_MIN_MTU || mtu > ETH_MAX_MTU)) {
die("MTU %lu out of range (%u..%u)", mtu,
ETH_MIN_MTU, ETH_MAX_MTU);
}
@@ -1980,9 +1976,6 @@ void conf(struct ctx *c, int argc, char **argv)
c->no_dhcpv6 = 1;
}
- if (!c->mtu)
- c->mtu = ROUND_DOWN(ETH_MAX_MTU - ETH_HLEN, sizeof(uint32_t));
-
get_dns(c);
if (!*c->pasta_ifn) {
diff --git a/dhcp.c b/dhcp.c
index 4a209f10..66a716e3 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -417,7 +417,7 @@ int dhcp(const struct ctx *c, const struct pool *p)
&c->ip4.guest_gw, sizeof(c->ip4.guest_gw));
}
- if (c->mtu != -1) {
+ if (c->mtu) {
opts[26].slen = 2;
opts[26].s[0] = c->mtu / 256;
opts[26].s[1] = c->mtu % 256;
diff --git a/ndp.c b/ndp.c
index 37bf7a35..ded2081d 100644
--- a/ndp.c
+++ b/ndp.c
@@ -256,7 +256,7 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
ptr = &ra.var[0];
- if (c->mtu != -1) {
+ if (c->mtu) {
struct opt_mtu *mtu = (struct opt_mtu *)ptr;
*mtu = (struct opt_mtu) {
.header = {
diff --git a/passt.h b/passt.h
index 1f0dab54..28d13892 100644
--- a/passt.h
+++ b/passt.h
@@ -274,6 +274,8 @@ struct ctx {
int fd_repair;
unsigned char our_tap_mac[ETH_ALEN];
unsigned char guest_mac[ETH_ALEN];
+ uint16_t mtu;
+
uint64_t hash_secret[2];
int ifi4;
@@ -298,7 +300,6 @@ struct ctx {
int no_icmp;
struct icmp_ctx icmp;
- int mtu;
int no_dns;
int no_dns_search;
int no_dhcp_dns;
diff --git a/pasta.c b/pasta.c
index 585a51c6..fa3e7de5 100644
--- a/pasta.c
+++ b/pasta.c
@@ -319,7 +319,7 @@ void pasta_ns_conf(struct ctx *c)
if (c->pasta_conf_ns) {
unsigned int flags = IFF_UP;
- if (c->mtu != -1)
+ if (c->mtu)
nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
if (c->ifi6) /* Avoid duplicate address detection on link up */
diff --git a/tcp.c b/tcp.c
index f498f5bc..e3c0a53b 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1139,7 +1139,7 @@ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn
*conn,
if (flags & SYN) {
int mss;
- if (c->mtu == -1) {
+ if (!c->mtu) {
mss = tinfo.tcpi_snd_mss;
} else {
mss = c->mtu - sizeof(struct tcphdr);
--
2.48.1