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fix: add compatibility flag to unalign first LBA #153

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fix: add compatibility flag to unalign first LBA #153

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7 changes: 6 additions & 1 deletion partitioning/gpt/gpt.go
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Original file line number Diff line number Diff line change
Expand Up @@ -287,7 +287,12 @@ func (t *Table) init(lastLBA uint64) {

if t.firstUsableLBA == 0 {
t.firstUsableLBA = t.primaryPartitionsLBA + uint64(lbasForEntries)
t.firstUsableLBA = (t.firstUsableLBA + t.alignment - 1) / t.alignment * t.alignment // 2048 with 512 sector size, 256 with 4096 sector size

// only align the LBA when the compatibility flag is not set. This alignment can cause Windows to corrupt the
// partition table.
if !t.options.CompatFirstUsableLBA {
t.firstUsableLBA = (t.firstUsableLBA + t.alignment - 1) / t.alignment * t.alignment // 2048 with 512 sector size, 256 with 4096 sector size
}
}

t.lastUsableLBA = t.secondaryPartitionsLBA - 1
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15 changes: 15 additions & 0 deletions partitioning/gpt/options.go
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Expand Up @@ -14,6 +14,12 @@ type Options struct {
// Number of LBAs to skip before the writing partition entries.
SkipLBAs uint

// If true, the first usable LBA will be the first LBA after the partition table.
// Otherwise (default), the first usable LBA will be set to the first LBA after
// the partition table aligned on a 1MiB boundary. Modern Windows versions can
// corrupt partition tables on disk eject when this flag is not set.
CompatFirstUsableLBA bool

// DiskGUID is a GUID for the disk.
//
// If not set, on partition table creation, a new GUID is generated.
Expand Down Expand Up @@ -51,6 +57,15 @@ func WithDiskGUID(guid uuid.UUID) Option {
}
}

// WithCompatFirstUsableLBA sets the first usable LBA to the first LBA after the
// partition table instead of a 1MiB-aligned value. This can prevent modern
// Windows versions from clobbering the partition table on disk eject.
func WithCompatFirstUsableLBA() Option {
return func(o *Options) {
o.CompatFirstUsableLBA = true
}
}

// PartitionOptions configure a partition.
type PartitionOptions struct {
UniqueGUID uuid.UUID
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