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--- net_device_attributes [2018/08/01 14:45] – [/sys/class/net/enp0s25/ files] rpjday
+++ net_device_attributes [2018/08/01 15:05] (current) – rpjday
@@ Line 1: / Line 1: @@
 ===== Overview =====
-Discussion about how net cable connect and disconnect are reflected in SYSFS.
+Discussion about how net cable connect and disconnect are reflected in ''/sys''.
 ===== /sys/class/net/enp3s0/ files =====
@@ Line 41: / Line 41: @@
 -r--r--r--. 1 root root 4096 Aug  1 10:41 type
 -rw-r--r--. 1 root root 4096 Aug  1 10:41 uevent
+</code>
+In particular, we care about the attributes that reflect physical connection (note how ''carrier'' is writeable):
+<code>
+-rw-r--r--. 1 root root 4096 Aug  1 10:41 carrier      [0 or 1]
+-r--r--r--. 1 root root 4096 Aug  1 10:41 operstate    [up or down]
+-rw-r--r--. 1 root root 4096 Aug  1 10:41 flags
+</code>
+===== flags =====
+==== 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 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 {
+        IFF_UP                          = 1<<0,  /* sysfs */
+        IFF_BROADCAST                   = 1<<1,  /* volatile */
+        IFF_DEBUG                       = 1<<2,  /* sysfs */
+        IFF_LOOPBACK                    = 1<<3,  /* volatile */
+        IFF_POINTOPOINT                 = 1<<4,  /* volatile */
+        IFF_NOTRAILERS                  = 1<<5,  /* sysfs */
+        IFF_RUNNING                     = 1<<6,  /* volatile */
+        IFF_NOARP                       = 1<<7,  /* sysfs */
+        IFF_PROMISC                     = 1<<8,  /* sysfs */
+        IFF_ALLMULTI                    = 1<<9,  /* sysfs */
+        IFF_MASTER                      = 1<<10, /* volatile */
+        IFF_SLAVE                       = 1<<11, /* volatile */
+        IFF_MULTICAST                   = 1<<12, /* sysfs */
+        IFF_PORTSEL                     = 1<<13, /* sysfs */
+        IFF_AUTOMEDIA                   = 1<<14, /* sysfs */
+        IFF_DYNAMIC                     = 1<<15, /* sysfs */
+        IFF_LOWER_UP                    = 1<<16, /* volatile */
+        IFF_DORMANT                     = 1<<17, /* volatile */
+        IFF_ECHO                        = 1<<18, /* volatile */
+};
+#define IFF_UP                          IFF_UP
+#define IFF_BROADCAST                   IFF_BROADCAST
+#define IFF_DEBUG                       IFF_DEBUG
+#define IFF_LOOPBACK                    IFF_LOOPBACK
+#define IFF_POINTOPOINT                 IFF_POINTOPOINT
+#define IFF_NOTRAILERS                  IFF_NOTRAILERS
+#define IFF_RUNNING                     IFF_RUNNING
+#define IFF_NOARP                       IFF_NOARP
+#define IFF_PROMISC                     IFF_PROMISC
+#define IFF_ALLMULTI                    IFF_ALLMULTI
+#define IFF_MASTER                      IFF_MASTER
+#define IFF_SLAVE                       IFF_SLAVE
+#define IFF_MULTICAST                   IFF_MULTICAST
+#define IFF_PORTSEL                     IFF_PORTSEL
+#define IFF_AUTOMEDIA                   IFF_AUTOMEDIA
+#define IFF_DYNAMIC                     IFF_DYNAMIC
+#define IFF_LOWER_UP                    IFF_LOWER_UP
+#define IFF_DORMANT                     IFF_DORMANT
+#define IFF_ECHO                        IFF_ECHO
+#define IFF_VOLATILE    (IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST|IFF_ECHO|\
+                IFF_MASTER|IFF_SLAVE|IFF_RUNNING|IFF_LOWER_UP|IFF_DORMANT)
 </code>