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/usb/core/usb.c

@@ -7,15 +7,15 @@
 // part of USB that is the same for every device ever made: read the
 // configuration, choose one, look at the interface, find someone who wants it.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "memlayout.h"
-#include "mmu.h"
-#include "spinlock.h"
-#include "dma.h"
-#include "usb.h"
-#include "hwinfo.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/memlayout.h"
+#include "arch/mmu.h"
+#include "core/spinlock.h"
+#include "core/dma.h"
+#include "dev/usb.h"
+#include "core/hwinfo.h"
 
 // A staging buffer for control transfers.
 //
@@ -130,7 +130,7 @@ parse_config(struct usb_dev *dev, int nth)
 }
 
 // One usb_dev for every interface after the first. See `base` in
-// include/usb.h. A fixed pool, like everything else here. It was sixteen,
+// include/dev/usb.h. A fixed pool, like everything else here. It was sixteen,
 // which a dock -- hub, Ethernet, audio, card reader, each two or three
 // interfaces -- and a couple of receivers already reach. 672 bytes each.
 #define NIFDEV 64

kernel/drivers/usb/hid/usb_hid.c

@@ -17,14 +17,14 @@
 // in the descriptor is stepped over. A boot mouse whose descriptor makes no
 // sense is still driven, in boot protocol, as before.
 
-#include "types.h"
-#include "defs.h"
-#include "gfx.h"
-#include "param.h"
-#include "spinlock.h"
-#include "dma.h"
-#include "usb.h"
-#include "input.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "gfx/gfx.h"
+#include "core/param.h"
+#include "core/spinlock.h"
+#include "core/dma.h"
+#include "dev/usb.h"
+#include "dev/input.h"
 
 #define NHID 8
 

kernel/drivers/usb/hub/usb_hub.c

@@ -15,12 +15,12 @@
 // translator rather than against the device. So this driver's real job is
 // less "operate the hub" than "tell the controller what shape the tree is".
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "spinlock.h"
-#include "dma.h"
-#include "usb.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "core/spinlock.h"
+#include "core/dma.h"
+#include "dev/usb.h"
 
 #define MAX_PORTS 15            // per hub; more than any real bus hub has
 #define NHUB      8

kernel/drivers/usb/storage/usb_storage.c

@@ -14,18 +14,18 @@
 // below (INQUIRY, READ CAPACITY, READ(10), WRITE(10)) are the same ones a
 // SCSI drive answered in 1990.
 
-#include "types.h"
-#include "defs.h"
-#include "param.h"
-#include "memlayout.h"
-#include "mmu.h"
-#include "spinlock.h"
-#include "sleeplock.h"
-#include "fs.h"
-#include "buf.h"
-#include "dma.h"
-#include "usb.h"
-#include "blkdev.h"
+#include "core/types.h"
+#include "core/defs.h"
+#include "core/param.h"
+#include "arch/memlayout.h"
+#include "arch/mmu.h"
+#include "core/spinlock.h"
+#include "core/sleeplock.h"
+#include "fs/fs.h"
+#include "fs/buf.h"
+#include "core/dma.h"
+#include "dev/usb.h"
+#include "fs/blkdev.h"
 
 #define CBW_SIGNATURE  0x43425355       // "USBC"
 #define CSW_SIGNATURE  0x53425355       // "USBS"