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/drivers/net/e1000/e1000.c

@@ -3,7 +3,7 @@
 // What it provides the rest of the system is a struct netdev_ops and nothing
 // else: a station address, a transmit path and a receive ring. It does not
 // know that lwIP exists, and lwIP does not know that it does -- see
-// include/netdev.h for why that boundary is where it is. Adding a second NIC
+// include/dev/netdev.h for why that boundary is where it is. Adding a second NIC
 // means writing another driver that fills in the same four function pointers,
 // and touching no file outside its own directory.
 //
@@ -13,21 +13,21 @@
 // receiver whose ring base is still zero makes the device DMA into physical
 // address 0, which on this kernel is the boot page table.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "x86.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "fs.h"
-#include "file.h"
-#include "mmu.h"
-#include "memlayout.h"
-#include "pci.h"
-#include "device.h"
-#include "netdev.h"
-#include "dma.h"
-#include "irq.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/x86.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/fs.h"
+#include "fs/file.h"
+#include "arch/mmu.h"
+#include "arch/memlayout.h"
+#include "dev/pci.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
+#include "core/dma.h"
+#include "core/irq.h"
 #include "e1000.h"
 
 struct e1000 {
@@ -477,7 +477,7 @@ e1000_release(struct pci_dev *d)
 }
 
 // Hang the instance on the device the bus has just published. See the comment
-// on `attached` in include/pci.h for why this cannot happen inside probe().
+// on `attached` in include/dev/pci.h for why this cannot happen inside probe().
 static void
 e1000_attached(struct pci_dev *d, struct device *dev)
 {

kernel/drivers/net/r8169/r8169.c

@@ -20,21 +20,21 @@
 // is Linux's: this is a descriptor-ring driver in the same shape as the e1000
 // beside it, because that is the shape this kernel's netdev class wants.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "x86.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "fs.h"
-#include "file.h"
-#include "memlayout.h"
-#include "mmu.h"
-#include "pci.h"
-#include "device.h"
-#include "netdev.h"
-#include "dma.h"
-#include "irq.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/x86.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/fs.h"
+#include "fs/file.h"
+#include "arch/memlayout.h"
+#include "arch/mmu.h"
+#include "dev/pci.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
+#include "core/dma.h"
+#include "core/irq.h"
 
 // --- registers --------------------------------------------------------------
 

kernel/drivers/net/rtl8139/rtl8139.c

@@ -12,21 +12,21 @@
 // and it is the one Realtek part QEMU emulates, so unlike the 8169 beside it
 // every line of this has been run.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "x86.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "fs.h"
-#include "file.h"
-#include "memlayout.h"
-#include "mmu.h"
-#include "pci.h"
-#include "device.h"
-#include "netdev.h"
-#include "dma.h"
-#include "irq.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/x86.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/fs.h"
+#include "fs/file.h"
+#include "arch/memlayout.h"
+#include "arch/mmu.h"
+#include "dev/pci.h"
+#include "dev/device.h"
+#include "dev/netdev.h"
+#include "core/dma.h"
+#include "core/irq.h"
 
 // --- registers --------------------------------------------------------------