d7352c0db0
q35 stopped with "no root filesystem" because its disk is SATA, like every PC since 2008, and SchOS only had IDE. And SchFS could only sit on a whole raw device, so nothing could boot from a disk that also carried an ESP. - include/blkdev.h, kernel/dev/blkdev.c: a registry of block devices found at probe time, numbered from 4. A disk's GPT (or MBR) is read when it registers, and each partition becomes a device whose block 0 is the partition's first sector. SchFS needs no format change to live in a partition; a Linux SchFS driver will see the same bytes on /dev/sdX2. SchFS has its own GPT type: 47138FA9-B79C-47A6-9F7D-AC1F7F572D5E. - AHCI driver, written from the AHCI 1.3.1 spec: BIOS handoff, COMRESET when the link is down, IDENTIFY, 48-bit DMA read/write, FLUSH. Completion is polled, so the root disk does not depend on interrupt routing. - USB sticks also register as usb0, so their partitions are found. - The root probe tries registered devices between USB and IDE, SchFS-typed partitions first. - make disk / tools/posix/mkdisk.sh: a GPT image with a 64 MB ESP and a SchFS partition, ready to dd to a stick or a disk. Tested in QEMU q35: the old two-disk setup roots on sata1; disk.img as the only SATA disk roots on sata0p2; disk.img as a USB stick (firmware boots from it) roots on usb0p2. Writes survive sync in each case. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01HH7xukt4aaiGj1nQEAoQf1
49 lines
2.3 KiB
C
49 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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#pragma once
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// Block devices that are found rather than assumed.
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//
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// The first four device numbers are fixed and always were: IDE 0 and 1, the
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// ramdisk, the first USB stick. Everything since -- a SATA disk behind AHCI,
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// an NVMe namespace, and every partition on any of them -- registers here at
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// probe time and is handed the next free number from BLKDEV_FIRST.
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//
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// A partition is a block device in its own right, with block 0 at its first
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// sector. That is the whole of partition support from a filesystem's side:
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// SchFS on /dev/sata0p2 sees a volume that starts at zero, exactly as it would
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// on a whole disk, and needs to know nothing about GPT -- which is also what
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// a Linux driver for SchFS will see when it is handed /dev/sda2.
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#define BLKDEV_FIRST 4
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#define NBLKDEV 16 // so device numbers stay below SCHFS_DEV (64)
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// The GPT partition type of a SchFS volume, as it is written and printed:
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// 47138FA9-B79C-47A6-9F7D-AC1F7F572D5E. sgdisk and fdisk accept it as is.
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// Generated for SchFS on 2026-10-22; nothing else uses it.
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#define SCHFS_GPT_TYPE "47138FA9-B79C-47A6-9F7D-AC1F7F572D5E"
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// What a driver supplies. `rw` moves `count` of the device's own sectors at
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// `lba` to or from `buf`, a kernel address; it is never asked for more than
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// BSIZE bytes at once. Returns 0, or -1 if the device refused.
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struct blkdev_ops {
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int (*rw)(void *priv, uint64 lba, uint32 count, void *buf, int write);
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int (*flush)(void *priv); // 0 when there is nothing to flush
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};
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// Register a whole disk. Its partition table, if it has one, is read here and
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// every partition registered after it. Returns the disk's device number, or
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// -1 if the table is full.
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int blkdev_register(const char *name, const struct blkdev_ops *ops,
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void *priv, uint64 nsectors, uint32 secsize);
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int blkdev_present(uint dev);
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void blkdev_rw(struct buf *b);
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int blkdev_flush(uint dev);
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// For the root probe: the registered devices in order, partitions after the
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// disk they are on. Returns the device number of the i'th, or -1 past the end.
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int blkdev_nth(int i);
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const char *blkdev_name(uint dev);
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int blkdev_is_schfs(uint dev); // a partition typed SCHFS_GPT_TYPE
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int blkdev_info(char *buf, int cap); // /proc/partitions
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