disk: part_efi: Fix backup GPT header placement for large sector sizes #10
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alchark
requested changes
Jan 20, 2026
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| if (offset > (last_usable_lba + 1)) { | ||
| log_debug("Partitions layout exceeds disk size\n"); | ||
| log_debug("Partitions layout exceeds disk size: %lu > %lu\n", offset, last_usable_lba + 1); |
Collaborator
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Long line, please wrap at the first comma
| gpt_h->alternate_lba = cpu_to_le64(desc->lba - 1); | ||
| gpt_h->last_usable_lba = cpu_to_le64(desc->lba - 34); | ||
| /* Reserve space for backup GPT header (1) + backup partition entries */ | ||
| gpt_h->last_usable_lba = cpu_to_le64(desc->lba - pte_sectors - 1); |
Collaborator
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-32 - 1 != -34
Please check
Contributor
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Yay. Seems like one sector lost for backup header.
The gpt_fill_header() function was incorrectly calculating the
last_usable_lba value using a hardcoded assumption about the partition
table entry (PTE) area size. This caused incorrect backup GPT placement
on disks with non-512-byte sector sizes.
The GPT specification requires 128 partition entries × 128 bytes = 16384
bytes for the partition entry array. For 512-byte sectors this requires
32 sectors, but for 4096-byte sectors only 4 sectors are needed.
Introduce a local pte_sectors variable that dynamically calculates the
number of sectors required for the partition entries based on the actual
block size:
pte_sectors = DIV_ROUND_UP(GPT_ENTRY_NUMBERS * sizeof(gpt_entry),
desc->blksz);
This ensures:
- last_usable_lba correctly reserves space for backup GPT header (1 block)
plus backup partition entries (pte_sectors blocks)
- first_usable_lba correctly accounts for the primary partition entries
starting at partition_entry_lba
The fix is essential for:
- Disks with 4K native sector size (i.e. UFS flashes)
- Proper GPT compliance across all sector size configurations
Change-Id: faf3cb2e-056d-458d-8abe-61edf2f40384
Signed-off-by: Anton Burticica <mouse@ya.ru>
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The gpt_fill_header() function was incorrectly calculating the last_usable_lba value using a hardcoded assumption about the partition table entry (PTE) area size. This caused incorrect backup GPT placement on disks with non-512-byte sector sizes.
The GPT specification requires 128 partition entries × 128 bytes = 16384 bytes for the partition entry array. For 512-byte sectors this requires 32 sectors, but for 4096-byte sectors only 4 sectors are needed.
Introduce a local pte_sectors variable that dynamically calculates the number of sectors required for the partition entries based on the actual block size:
This ensures:
The fix is essential for:
Change-Id: faf3cb2e-056d-458d-8abe-61edf2f40384