Claude
e94cd3245d
The old MBR zeroed first, the backup header and entries, the primary, the protective MBR last: a write torn anywhere leaves no table. Builds clean on amd64, aarch64, riscv64; checked on the host against blank 600 MiB and 32 MiB images and a used Zuse stick (sfdisk --verify clean, gpt_read reads it back). Not yet called. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2
82 lines
4.0 KiB
C
82 lines
4.0 KiB
C
/* gpt.h -- the GPT reader, and a block device of one partition.
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* docs/v4.0.0/STICK.md 3 and 4; docs/v4.0.0/plans/2026-10-26-stick-2-gpt-reader.md.
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*/
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#ifndef STARKERNEL_GPT_H
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#define STARKERNEL_GPT_H
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#include <stdint.h>
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#include <stddef.h>
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#include "blkio.h"
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/* The two StarshipOS partition types, as their GUIDs are on disk. */
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extern const uint8_t gpt_type_starship_identity[16]; /* 23BEBFE1-4817-4CF3-A537-9069BF159788 */
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extern const uint8_t gpt_type_starship_artemis[16]; /* BCD7B586-1C8E-4EEF-86A3-273A8D8EE624 */
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typedef struct {
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uint8_t type[16];
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uint64_t first_lba;
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uint64_t last_lba;
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} gpt_part_t;
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#define GPT_OK 0 /* a valid GPT */
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#define GPT_NONE 1 /* not a GPT disk -- no protective MBR -- (or one whose sectors are not 512 bytes): read it raw */
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#define GPT_BAD 2 /* a protective MBR, but its header or entry array does not check out: not used */
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#define GPT_EIO 3 /* its first block could not be read: not used */
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/* Read `disk`'s protective MBR, primary GPT header and partition-entry array,
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* checking both CRC-32s, the revision, the sizes and the geometry. On GPT_OK,
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* `*count` partitions with a non-zero type (at most `max`) are in `parts`.
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* Reads only. */
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int gpt_read(blkio_dev_t *disk, gpt_part_t *parts, unsigned max, unsigned *count);
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/* The DiskGUID (header bytes 56..71, as on disk) of the last gpt_read that
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* returned GPT_OK: which disk it was, so a stick can be told from another. */
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void gpt_disk_guid(uint8_t guid[16]);
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/* The backup header's LBA (header bytes 32..39) of the last gpt_read that
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* returned GPT_OK: a disk whose backup header is not its last sector is larger
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* than the table written to it. */
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uint64_t gpt_alternate_lba(void);
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/* Grow the partition of `type` -- which must be the disk's last -- to the end
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* of `disk` (plan 2026-10-29-stick-5, Task 2): the backup entry array and
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* header moved to the disk's last sectors, the partition's last LBA to the
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* last usable sector before them (on a whole MiB, at most `max_part_sectors`
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* long), both headers rewritten with their CRCs -- the backup first, so a
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* write torn between them leaves the old primary valid -- and the protective
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* MBR's size. GPT_OK with `*new_last_lba` the partition's last LBA (unchanged,
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* and nothing written, when the backup header is already the disk's last
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* sector); GPT_BAD or GPT_EIO otherwise. */
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int gpt_grow_last(blkio_dev_t *disk, const uint8_t type[16], uint64_t max_part_sectors, uint64_t *new_last_lba);
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/* Write a new GPT on `disk` with one partition of `type` (plan
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* 2026-10-29-stick-5, Task 4: the real Zuse's stick): at LBA 2048, at most
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* `part_sectors` long (on a whole MiB, no further than the disk allows), a
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* fresh DiskGUID (into `disk_guid`) and partition GUID from the RNG, 128
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* entries, the backup header and entries at the disk's end, the protective
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* MBR written last (the old one zeroed first, so a write torn anywhere leaves
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* no table). Nothing inside the partition is written. GPT_OK; GPT_BAD for a
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* disk whose sectors are not 512 bytes or that is too small; GPT_EIO. */
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int gpt_write_one(blkio_dev_t *disk, const uint8_t type[16], uint64_t part_sectors, uint8_t disk_guid[16]);
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/* The index of the first partition of `type`, or -1. */
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int gpt_find(const gpt_part_t *parts, unsigned count, const uint8_t type[16]);
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/* A partition as a block device: its block n is the disk's block
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* first_fblock + n; blocks past fblocks are refused. */
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typedef struct {
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blkio_dev_t *disk;
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uint32_t first_fblock;
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uint32_t fblocks;
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} gpt_part_dev_t;
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/* Open `dev` as partition `p` of `disk`, its state in `st` (which must live
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* as long as `dev`). BLKIO_EINVAL for a partition that does not start and end
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* on a 1 KiB block, or that runs past the disk. */
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int gpt_part_open(blkio_dev_t *dev, gpt_part_dev_t *st, blkio_dev_t *disk, const gpt_part_t *p);
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/* CRC-32 (IEEE 802.3, reflected, polynomial 0xEDB88320), as GPT uses. */
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uint32_t gpt_crc32(const void *buf, size_t len);
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#endif /* STARKERNEL_GPT_H */
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