Re: [PATCH net-next v2] ipv6: add IFLA_INET6_RA_MTU to expose mtu value in the RA message
From: David Ahern <hidden>
Date: 2021-07-31 17:18:01
Also in:
linux-mediatek, lkml, netdev
On 7/30/21 7:52 PM, Rocco Yue wrote:
The kernel provides a "/proc/sys/net/ipv6/conf/<iface>/mtu" file, which can temporarily record the mtu value of the last received RA message when the RA mtu value is lower than the interface mtu, but this proc has following limitations: (1) when the interface mtu (/sys/class/net/<iface>/mtu) is updeated, mtu6 (/proc/sys/net/ipv6/conf/<iface>/mtu) will be updated to the value of interface mtu; (2) mtu6 (/proc/sys/net/ipv6/conf/<iface>/mtu) only affect ipv6 connection, and not affect ipv4. Therefore, when the mtu option is carried in the RA message, there will be a problem that the user sometimes cannot obtain RA mtu value correctly by reading mtu6. After this patch set, if a RA message carries the mtu option, you can send a netlink msg which nlmsg_type is RTM_GETLINK, and then by parsing the attribute of IFLA_INET6_RA_MTU to get the mtu value carried in the RA message received on the inet6 device. In this way, if the MTU values that the device receives from the network in the PCO IPv4 and the RA IPv6 procedures are different, the user space process can read ra_mtu to get the mtu value carried in the RA message without worrying about the issue of ipv4 being stuck due to the late arrival of RA message. After comparing the value of ra_mtu and ipv4 mtu, then the device can use the lower MTU value for both IPv4 and IPv6.
you are storing the value and sending to userspace but never using it when sending a message. What's the pointing of processing the MTU in the RA if you are not going to use it to control message size?
quoted hunk ↗ jump to hunk
Signed-off-by: Rocco Yue <redacted> --- include/net/if_inet6.h | 2 ++ include/uapi/linux/if_link.h | 1 + net/ipv6/addrconf.c | 5 +++++ net/ipv6/ndisc.c | 5 +++++ tools/include/uapi/linux/if_link.h | 1 + 5 files changed, 14 insertions(+)diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h index 4882e81514b6..fcd1ae29f154 100644 --- a/include/uapi/linux/if_link.h +++ b/include/uapi/linux/if_link.h@@ -417,6 +417,7 @@ enum { IFLA_INET6_ICMP6STATS, /* statistics (icmpv6) */ IFLA_INET6_TOKEN, /* device token */ IFLA_INET6_ADDR_GEN_MODE, /* implicit address generator mode */ + IFLA_INET6_RA_MTU, /* mtu carried in the RA message */ __IFLA_INET6_MAX };diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 3bf685fe64b9..98eeaba9f86c 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c@@ -5537,6 +5537,7 @@ static inline size_t inet6_ifla6_size(void) + nla_total_size(ICMP6_MIB_MAX * 8) /* IFLA_INET6_ICMP6STATS */ + nla_total_size(sizeof(struct in6_addr)) /* IFLA_INET6_TOKEN */ + nla_total_size(1) /* IFLA_INET6_ADDR_GEN_MODE */ + + nla_total_size(4) /* IFLA_INET6_RA_MTU */ + 0; }@@ -5645,6 +5646,9 @@ static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev, if (nla_put_u8(skb, IFLA_INET6_ADDR_GEN_MODE, idev->cnf.addr_gen_mode)) goto nla_put_failure; + if (nla_put_u32(skb, IFLA_INET6_RA_MTU, idev->ra_mtu)) + goto nla_put_failure; + return 0; nla_put_failure:@@ -5761,6 +5765,7 @@ static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token, static const struct nla_policy inet6_af_policy[IFLA_INET6_MAX + 1] = { [IFLA_INET6_ADDR_GEN_MODE] = { .type = NLA_U8 }, [IFLA_INET6_TOKEN] = { .len = sizeof(struct in6_addr) }, + [IFLA_INET6_RA_MTU] = { .type = NLA_U32 }, }; static int check_addr_gen_mode(int mode)
Its value is derived from an RA not set by userspace, so set the type to NLA_REJECT so that inet6_validate_link_af will reject messages that have IFLA_INET6_RA_MTU set. You can set "reject_message" in the policy to return a message that "IFLA_INET6_RA_MTU can not be set". _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel