include: one folder per subsystem, and includes that name it

Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".

Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

kernel/net/inet.c

@@ -47,17 +47,17 @@
 // in the ones with nothing to do, and a per-socket channel would have to be
 // torn down carefully in close() against callbacks that can still arrive.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "proc.h"
-#include "fs.h"      /* NDIRECT, which file.h's struct inode needs */
-#include "file.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "core/proc.h"
+#include "fs/fs.h"      /* NDIRECT, which file.h's struct inode needs */
+#include "fs/file.h"
 #define _KERNEL_SOCKET_INTERNALS
-#include "socket.h"
-#include "errno.h"
+#include "net/socket.h"
+#include "uapi/errno.h"
 
 #include "lwip/opt.h"
 #include "lwip/tcp.h"

kernel/net/lwip/arch/cc.h

@@ -10,8 +10,8 @@
 #ifndef LWIP_ARCH_CC_H
 #define LWIP_ARCH_CC_H
 
-#include "types.h"
-#include "defs.h"
+#include "core/types.h"
+#include "core/defs.h"
 
 // There is no libc under the kernel, so every header lwIP would normally reach
 // for has to be switched off and its contents supplied here instead. That is

kernel/net/lwip/netif_eth.c

@@ -7,18 +7,18 @@
 // driver, and this file knows only that a network device can transmit a frame,
 // receive a frame and state its MAC address. It was `netif_e1000.c` and called
 // `e1000_transmit` directly, which meant the second NIC driver would have
-// arrived with a second near-identical copy of this file. See include/netdev.h.
+// arrived with a second near-identical copy of this file. See include/dev/netdev.h.
 //
 // One netif per bound interface, up to NETIF_MAX. Two NICs is an ordinary
 // machine -- a laptop with Ethernet and the virtual one QEMU adds is already
 // two -- and the limit exists only because a fixed array is simpler than
 // allocation for something enumerated once at boot.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "device.h"
-#include "netdev.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
 
 #include "lwip/opt.h"
 #include "lwip/netif.h"

kernel/net/lwip/sys_arch.c

@@ -24,12 +24,12 @@
 // It is recursive by necessity: lwIP brackets small critical sections inside
 // larger ones and expects nesting to be free.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "proc.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "core/proc.h"
 
 #include "lwip/opt.h"
 #include "lwip/sys.h"

kernel/net/net.c

@@ -10,7 +10,7 @@
 // register -- and this thread polls.
 //
 // Nothing here names a driver. Interfaces come from the netdev class
-// (include/netdev.h): every bound network device is attached, and a machine
+// (include/dev/netdev.h): every bound network device is attached, and a machine
 // with two NICs gets two interfaces without a line changing in this file.
 //
 // Polling costs a wakeup every few milliseconds when the link is idle. The
@@ -18,14 +18,14 @@
 // later; it is deliberately not the first version, because a receive path that
 // is woken from an interrupt is much harder to debug than one that is asked.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "proc.h"
-#include "device.h"
-#include "netdev.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "core/proc.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
 
 #include "lwip/opt.h"
 #include "lwip/init.h"

kernel/net/netlink.c

@@ -18,24 +18,24 @@
 // musl passes -- is trivially honoured.
 //
 // The information is not this file's. Interfaces come from the netdev class
-// (include/netdev.h) and addresses from lwIP's netifs, exactly as /proc/netif
+// (include/dev/netdev.h) and addresses from lwIP's netifs, exactly as /proc/netif
 // reads them. Nothing here knows what an e1000 is.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "mmu.h"
-#include "proc.h"
-#include "fs.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "file.h"
-#include "errno.h"
-#include "device.h"
-#include "netdev.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/mmu.h"
+#include "core/proc.h"
+#include "fs/fs.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/file.h"
+#include "uapi/errno.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
 
 #define _KERNEL_SOCKET_INTERNALS
-#include "socket.h"
+#include "net/socket.h"
 
 #include "lwip/netif.h"
 #include "lwip/ip4_addr.h"

kernel/net/unix.c

@@ -25,22 +25,22 @@
 // socket path failing with ENOENT. Both are worth fixing when the VFS next
 // gets opened up; neither blocks anything.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "mmu.h"
-#include "proc.h"
-#include "fs.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "file.h"
-#include "posix.h"
-#include "errno.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/mmu.h"
+#include "core/proc.h"
+#include "fs/fs.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/file.h"
+#include "uapi/posix.h"
+#include "uapi/errno.h"
 
 #define _KERNEL_SOCKET_INTERNALS
-#include "socket.h"
-#include "sbuf.h"
-#include "dbg.h"
+#include "net/socket.h"
+#include "core/sbuf.h"
+#include "core/dbg.h"
 
 static struct {
   struct spinlock lock;