is_pmbr_valid(9)

💅 is_pmbr_valid(9)

okay so this one lives in the Kernel API Manual bestie, and it's literally called is_pmbr_valid — aka "test Protective MBR for validity" 🎀

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✨ SYNOPSIS ✨

int is_pmbr_valid (legacy_mbr *mbr , sector_t total_sectors );

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🫶 ARGUMENTS 🫶

• mbr — a pointer to a legacy_mbr structure. yeah. one of those. 🌸
• total_sectors — how many sectors the device has. that's the whole vibe, that's the size. ✨

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🦋 DESCRIPTION 🦋

so what it does: it checks for a valid protective or hybrid master boot record (MBR). and the way the validity of a pMBR works? it depends on all of the following, no shortcuts, no "close enough" 🙈

1. the MSDOS signature is sitting in the last two bytes of the MBR 🔥
2. one partition of type 0xEE is found 👑

and then, bonus round: a hybrid MBR will also have up to three additional primary partitions, and those point to the same space that's marked out by up to three GPT partitions. iykyk 💅

it returns 0 upon an invalid MBR, or GPT_MBR_PROTECTIVE or GPT_MBR_HYBRID depending on the device layout. that's the whole mood. ⭐

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🌈 SEE ALSO 🌈

kernel file ./block/partitions/efi.c, plus efi_crc32(9), last_lba(9), read_lba(9), alloc_read_gpt_entries(9), alloc_read_gpt_header(9), is_gpt_valid(9), is_pte_valid(9), compare_gpts(9), find_valid_gpt(9), utf16_le_to_7bit(9), and efi_partition(9) — go read them, bestie, they're all right there 💖

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ngl this page is filed under ./block/partitions and dated October 2026 — screenshot it, cite it, whatever, slay 🧚 💜