Differences

This shows you the differences between two versions of the page.

--- ipp_up_and_iff_running [2018/08/25 16:08] – rpjday
+++ ipp_up_and_iff_running [2018/08/27 11:03] (current) – [net/core/dev_ioctl.c] rpjday
@@ Line 8: / Line 8: @@
 ===== Flags =====
+Issues:
+  * Is ''IFF_LOWER_UP'' significant?
+  * Can we use ''IFF_DEBUG''?
+  * Understand actual meaning of "volatile".
 From ''include/uapi/linux/if.h'':
 <code>
+/**
+ * enum net_device_flags - &struct net_device flags
+ *
+ * These are the &struct net_device flags, they can be set by drivers, the
+ * kernel and some can be triggered by userspace. Userspace can query and
+ * set these flags using userspace utilities but there is also a sysfs
+ * entry available for all dev flags which can be queried and set. These flags
+ * are shared for all types of net_devices. The sysfs entries are available
+ * via /sys/class/net/<dev>/flags. Flags which can be toggled through sysfs
+ * are annotated below, note that only a few flags can be toggled and some
+ * other flags are always preserved from the original net_device flags
+ * even if you try to set them via sysfs. Flags which are always preserved
+ * are kept under the flag grouping @IFF_VOLATILE. Flags which are volatile
+ * are annotated below as such.
+ *
+ * You should have a pretty good reason to be extending these flags.
+ *
+ * @IFF_UP: interface is up. Can be toggled through sysfs.
+ * @IFF_BROADCAST: broadcast address valid. Volatile.
+ * @IFF_DEBUG: turn on debugging. Can be toggled through sysfs.
+ * @IFF_LOOPBACK: is a loopback net. Volatile.
+ * @IFF_POINTOPOINT: interface is has p-p link. Volatile.
+ * @IFF_NOTRAILERS: avoid use of trailers. Can be toggled through sysfs.
+ *      Volatile.
+ * @IFF_RUNNING: interface RFC2863 OPER_UP. Volatile.
+ * @IFF_NOARP: no ARP protocol. Can be toggled through sysfs. Volatile.
+ * @IFF_PROMISC: receive all packets. Can be toggled through sysfs.
+ * @IFF_ALLMULTI: receive all multicast packets. Can be toggled through
+ *      sysfs.
+ * @IFF_MASTER: master of a load balancer. Volatile.
+ * @IFF_SLAVE: slave of a load balancer. Volatile.
+ * @IFF_MULTICAST: Supports multicast. Can be toggled through sysfs.
+ * @IFF_PORTSEL: can set media type. Can be toggled through sysfs.
+ * @IFF_AUTOMEDIA: auto media select active. Can be toggled through sysfs.
+ * @IFF_DYNAMIC: dialup device with changing addresses. Can be toggled
+ *      through sysfs.
+ * @IFF_LOWER_UP: driver signals L1 up. Volatile.
+ * @IFF_DORMANT: driver signals dormant. Volatile.
+ * @IFF_ECHO: echo sent packets. Volatile.
+ */
 enum net_device_flags {
 /* for compatibility with glibc net/if.h */
@@ Line 38: / Line 85: @@
 #endif /* __UAPI_DEF_IF_NET_DEVICE_FLAGS_LOWER_UP_DORMANT_ECHO */
 };
+</code>
+===== operstates.txt =====
+Administrative versus operational state:
+<code>
+Linux distinguishes between administrative and operational state of an
+interface. Administrative state is the result of "ip link set dev
+<dev> up or down" and reflects whether the administrator wants to use
+the device for traffic.
+However, an interface is not usable just because the admin enabled it
+- ethernet requires to be plugged into the switch and, depending on
+a site's networking policy and configuration, an 802.1X authentication
+to be performed before user data can be transferred. Operational state
+shows the ability of an interface to transmit this user data.
+Thanks to 802.1X, userspace must be granted the possibility to
+influence operational state. To accommodate this, operational state is
+split into two parts: Two flags that can be set by the driver only, and
+a RFC2863 compatible state that is derived from these flags, a policy,
+and changeable from userspace under certain rules.
+</code>
+===== Flags =====
+==== Source ====
+''ifconfig'' is getting hex value from ''SIOCGIFFLAGS'' which does ''dev_get_flags(dev)''.
+==== Up and running ====
+:
+<code>
+enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
+        inet 192.168.0.15  netmask 255.255.255.0  broadcast 192.168.0.255
+        inet6 fd00:f81d:f81:4062:2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x0<global>
+        inet6 fe80::2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x20<link>
+        ether 2c:56:dc:25:ad:47  txqueuelen 1000  (Ethernet)
+        RX packets 81232  bytes 92092778 (87.8 MiB)
+        RX errors 0  dropped 0  overruns 0  frame 0
+        TX packets 36768  bytes 9024553 (8.6 MiB)
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+</code>
+==== Down ====
+:
+<code>
+enp3s0: flags=4098<BROADCAST,MULTICAST>  mtu 1500
+        inet 192.168.0.15  netmask 255.255.255.0  broadcast 192.168.0.255
+        ether 2c:56:dc:25:ad:47  txqueuelen 1000  (Ethernet)
+        RX packets 81290  bytes 92110209 (87.8 MiB)
+        RX errors 0  dropped 0  overruns 0  frame 0
+        TX packets 36836  bytes 9042100 (8.6 MiB)
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+</code>
+==== Up again ====
+UP, shortly followed by RUNNING:
+<code>
+enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
+        inet 192.168.0.15  netmask 255.255.255.0  broadcast 192.168.0.255
+        inet6 fd00:f81d:f81:4062:2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x0<global>
+        inet6 fe80::2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x20<link>
+        ether 2c:56:dc:25:ad:47  txqueuelen 1000  (Ethernet)
+        RX packets 1268514  bytes 1611028865 (1.5 GiB)
+        RX errors 0  dropped 0  overruns 0  frame 0
+        TX packets 396222  bytes 65965632 (62.9 MiB)
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+</code>
+==== Up, then disconnected ====
+:
+<code>
+enp3s0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
+        inet 192.168.0.15  netmask 255.255.255.0  broadcast 192.168.0.255
+        inet6 fd00:f81d:f81:4062:2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x0<global>
+        inet6 fe80::2e56:dcff:fe25:ad47  prefixlen 64  scopeid 0x20<link>
+        ether 2c:56:dc:25:ad:47  txqueuelen 1000  (Ethernet)
+        RX packets 81318  bytes 92115343 (87.8 MiB)
+        RX errors 0  dropped 0  overruns 0  frame 0
+        TX packets 36917  bytes 9052750 (8.6 MiB)
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+</code>
+===== dev_get_flags() =====
+==== net/core/dev_ioctl.c ====
+This is how ''ifconfig'' gets its info -- via ''dev_get_flags()'' and ioctl command ''SIOCGIFFLAGS'':
+<code>
+/*
+ *      Perform the SIOCxIFxxx calls, inside rcu_read_lock()
+ */
+static int dev_ifsioc_locked(struct net *net, struct ifreq *ifr, unsigned int cmd)
+{
+        int err;
+        struct net_device *dev = dev_get_by_name_rcu(net, ifr->ifr_name);
+        if (!dev)
+                return -ENODEV;
+        switch (cmd) {
+        case SIOCGIFFLAGS:      /* Get interface flags */
+                ifr->ifr_flags = (short) dev_get_flags(dev);
+                return 0;
+</code>
+==== net/core/dev.c ====
+Volatile flags are supported via RFC2863 operstates.
+<code>
+/**
+ *	dev_get_flags - get flags reported to userspace
+ *	@dev: device
+ *
+ *	Get the combination of flag bits exported through APIs to userspace.
+ */
+unsigned int dev_get_flags(const struct net_device *dev)
+{
+	unsigned int flags;
+	flags = (dev->flags & ~(IFF_PROMISC |
+				IFF_ALLMULTI |
+				IFF_RUNNING |
+				IFF_LOWER_UP |
+				IFF_DORMANT)) |
+		(dev->gflags & (IFF_PROMISC |
+				IFF_ALLMULTI));
+	if (netif_running(dev)) {
+		if (netif_oper_up(dev))
+			flags |= IFF_RUNNING;
+		if (netif_carrier_ok(dev))
+			flags |= IFF_LOWER_UP;
+		if (netif_dormant(dev))
+			flags |= IFF_DORMANT;
+	}
+	return flags;
+}
+EXPORT_SYMBOL(dev_get_flags);
 </code>