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disk: dynamically calculate header & footer

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Instead of just reserving a fixed amount of sectors for the
partition header and footer, calculate the size of the
header and footer dynamically when the layout is GPT.
This commit is contained in:
Christian Kellner 2021-12-31 15:34:40 +01:00 • committed by Tom Gundersen
parent b65ef74cb2
commit abaadf95ed
1 changed files with 26 additions and 11 deletions
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37
internal/disk/disk.go
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@ -345,8 +345,27 @@ func (pt *PartitionTable) GenerateUUIDs(rng *rand.Rand) {
// Returns the updated start point.
func (pt *PartitionTable) updatePartitionStartPointOffsets(size uint64) uint64 {
// initial alignment
start := pt.AlignUp(0)
// always reserve one extra sector for the GPT header
header := uint64(1)
footer := uint64(0)
if pt.Type == "gpt" {
// calculate the space we need for
parts := len(pt.Partitions)
// reserver a minimum of 128 partition entires
if parts < 128 {
parts = 128
}
nBytes := uint64(parts * 128)
header += pt.BytesToSectors(nBytes)
footer = header
}
start := pt.AlignUp(header)
size = pt.SectorsToBytes(pt.AlignUp(pt.BytesToSectors(size) - 1))
var rootIdx = -1
@ -364,16 +383,12 @@ func (pt *PartitionTable) updatePartitionStartPointOffsets(size uint64) uint64 {
root := &pt.Partitions[rootIdx]
root.Start = start
// Calculate the room at the end of the partition table that
// we might need to leave empty
padding := pt.ExtraPadding
if pt.Type == "gpt" {
padding += 33 // 33 sectors for the secondary GPT header
}
// add the extra pedding specified in the partition table
footer += pt.ExtraPadding
// If the sum of all partitions is bigger then the specified size,
// we use that instead. Grow the partition table size if needed.
end := pt.AlignUp(root.Start + padding + root.Size - 1)
end := pt.AlignUp(root.Start + footer + root.Size - 1)
if endBytes := pt.SectorsToBytes(end); endBytes > size {
size = endBytes
}
@ -386,8 +401,8 @@ func (pt *PartitionTable) updatePartitionStartPointOffsets(size uint64) uint64 {
root.Size = pt.BytesToSectors(pt.Size) - root.Start
// Finally we shrink the last partition, i.e. the root partition,
// to leave space for the secondary GPT header.
root.Size -= padding
// to leave space for the footer, e.g. the secondary GPT header.
root.Size -= footer
return start
}