storage: NVMe, so a laptop's SSD is a disk SchOS can boot from

A native driver written from the NVMe 1.4 base specification. It resets
the controller the firmware left running, then sets up an admin queue and
one I/O queue pair. Completion is polled, with interrupts disabled at the
queue, for the same reason AHCI polls: without AML, interrupt routing on
real hardware cannot be trusted. Each active namespace with 512-byte to
4 KB sectors and no metadata is registered as nvme<C>n<N>, the name
Linux uses, and its GPT is read like any other disk's.

Tested under QEMU q35: disk.img on NVMe as the only disk boots through
OVMF, roots on nvme0n1p2, and writes read back after sync. A
4 KB-sector namespace registers.

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

docs/architecture/boot.md

@@ -454,8 +454,9 @@ what makes a loop over candidates legal at all.
 
 The **registered** devices are the ones found at probe time rather than known
 at build time, numbered from 4 (`include/blkdev.h`): a SATA disk behind AHCI
-(`sata0`), the USB stick seen a second time (`usb0`), and every partition on
-either (`sata0p2`, `usb0p2`). When a disk registers, its GPT is read, or its MBR
+(`sata0`), an NVMe namespace (`nvme0n1`), each USB stick (`usb0`..`usb3`, the
+first of them also seen as device 3), and every partition on any of them
+(`sata0p2`, `nvme0n1p2`, `usb0p2`). When a disk registers, its GPT is read, or its MBR
 if it has no GPT. Each partition then becomes a device whose block 0 is the
 partition's first sector, so SchFS in a partition and SchFS on a whole disk are
 the same bytes. The ESP is skipped because it is FAT.
@@ -606,10 +607,10 @@ in the one process that runs first.
   stall, which is the wrong order for finding out.
 - **`/proc/bootmode` is read once, at start.** A program that wants to be
   quieter or louder later has nowhere to say so, and nothing re-reads it.
-- **One USB disk, found at boot.** The mass-storage driver drives the first
-  stick and no other, and a stick plugged in later is not seen. See
-  [usb.md](usb.md).
-- **No NVMe yet.** SATA (AHCI) and IDE are the only fixed disks.
+- **The root is chosen once, at boot.** A stick plugged in later is registered
+  with its partitions, but nothing mounts it. See [usb.md](usb.md).
+- **NVMe and AHCI poll for completion**, one command at a time per disk. That
+  is enough to boot and run from them, not to be fast.
 - **`make ramroot` is the only way to boot with no data disk.** It links a
   filesystem image into the kernel binary, which costs boot time and carries a
   licensing constraint — see [../licensing.md](../licensing.md) §4.

docs/plan/roadmap.md

@@ -19,8 +19,11 @@ root is chosen at boot from what is present (`rootdev_mount()` in
 `kernel/proc/proc.c`), and `make disk` builds a GPT image with an ESP and a SchFS
 partition that a PC boots from a stick or a disk.
 
-**Next: NVMe**, through the same block registry, and an installer that writes
-that layout to a disk.
+NVMe (`kernel/drivers/storage/nvme/`) registers with the same block registry,
+so an NVMe SSD boots the same way.
+
+**Next:** an installer that writes that layout to a disk, and interrupt-driven,
+queued I/O for AHCI and NVMe.
 
 ## 2. Graphics