udev works: /sys device tree, uevent netlink, datagram sockets with per-message credentials

Kernel devices (input, mem, tty, graphics, block) get /sys/devices/virtual
entries with dev/uevent/subsystem, /sys/class and /sys/dev links, input
capabilities, and writable uevent files that announce on the netlink socket.
eudev now runs, processes a full trigger and settles.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EVRhxi9zpdW2uDUN4FVcao

include/core/defs.h

@@ -541,7 +541,13 @@ int             sock_shutdown(struct socket*, int how);
 int             sockpair(struct socket **a, struct socket **b);
 int             sockpair_type(struct socket **a, struct socket **b, int type);
 int             sock_is_packet(struct socket *s);
-int             sock_netlink_bind(struct socket *s, uint groups);
+uint            sock_nl_groups(struct socket *s);
+int             sock_netlink_bind(struct socket *s, uint pid, uint groups);
+int             sock_uevent_send(struct socket *s, const char *msg, int len, uint dpid, uint dgroups);
+uint            sock_nl_from(struct socket *s);
+uint            sock_nl_pid(struct socket *s);
+uint            sock_nl_bound_groups(struct socket *s);
+void            dev_stat_numbers(int major, int minor, int *maj, int *min);
 void            uevent_send(uint groups, const char *msg, int len, struct socket *from);
 const char*     sockname(struct socket*);
 // AF_INET addressing. Separate from sockbind/sockconnect because the families

include/dev/kdev.h

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+//
+// The devices the kernel implements itself, as /sys and udev see them.
+//
+// /dev holds them already (kernel/fs/devfs.c). This is the other half of what
+// udev needs: for each node a place in /sys/devices, the class and dev/ links
+// that lead back to it, the facts udev's rules read (MAJOR, MINOR, DEVNAME,
+// input capabilities), and a way to announce it on the uevent netlink socket.
+#pragma once
+
+#include "core/types.h"
+
+#define KDEV_NAME     24
+#define KDEV_DEVNAME  32
+#define KDEV_BLK0     256       // kdev indexes from here are block devices
+
+enum { KD_NONE, KD_KEYBOARD, KD_MOUSE };
+
+struct kdev {
+  char  subsys[16];             // class: input, mem, tty, graphics, block
+  char  name[KDEV_NAME];        // directory name under the parent
+  char  devname[KDEV_DEVNAME];  // path below /dev, "" for a device with no node
+  short major, minor;
+  int   block;
+  int   parent;                 // kdev index of the device it hangs off, or -1
+  int   cap;                    // KD_*: what an input device can do
+};
+
+int  kdev_nsubsys(void);
+const char *kdev_subsys(int s);
+
+// Index of the Nth device that exists, 0.. until -1.
+int  kdev_nth(int n);
+int  kdev_get(int i, struct kdev *k);
+// The numbers stat() shows for its node, which are what /sys must show too.
+void kdev_numbers(const struct kdev *k, int *maj, int *min);
+
+// "devices/virtual/input/input0/event0": where it lives below /sys.
+int  kdev_path(int i, char *buf, int cap);
+
+// Announce a device on the uevent socket: action is "add", "remove", "change".
+void kdev_uevent(int i, const char *action);
+// What reading a device's `uevent` file says.
+int  kdev_uevent_text(int i, char *buf, int cap);

include/net/socket.h

@@ -344,6 +344,11 @@ struct socket {
   // AF_NETLINK only: which protocol, and the multicast groups bound.
   int   nlproto;
   uint  nlgroups;
+  uint  nlpid;                  // port id, assigned at bind
+  uint  nllast;                 // groups of the datagram read last
+  uint  nlfrom;                 // port id (netlink) or pid (Unix) of its sender
+  uint  pk_uid, pk_gid;         // Unix packet: credentials of its sender
+  int   pk_valid;               // a packet has been read
 
   // Connections waiting to be accepted, on a listener.
   struct socket *queue[NBACKLOG];