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discover: fix sysfs end-of-partition calculation #7

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discover: fix sysfs end-of-partition calculation #7

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6 changes: 5 additions & 1 deletion discover.go
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Original file line number Diff line number Diff line change
Expand Up @@ -172,7 +172,11 @@ func findDisks(disk, syspath string) (map[string][]partitionData, error) {
if err != nil {
return nil, err
}
end := size - start + 1
// sysfs reports `size` as the partition's length in sectors
// (not its last LBA), so the inclusive last sector is
// start + size - 1. The disk-image branch above uses the
// same formula.
end := start + size - 1
// read from uevent to get name
ueventPath := filepath.Join(sysClassBlockPath, candidate.Name(), name, "uevent")
ueventData, err := os.ReadFile(ueventPath)
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8 changes: 7 additions & 1 deletion discover_test.go
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Expand Up @@ -133,11 +133,17 @@ func TestFindDisks(t *testing.T) {
if pd.label != "foo" {
t.Errorf("pd.label = %q, want foo", pd.label)
}
// start and size in bytes (blockSize=512)
// start, size, and end in bytes (blockSize=512). End is the
// inclusive last byte of the partition, i.e.
// (start_sector + size_sectors - 1) * blockSize.
if pd.start != 2*512 || pd.size != 4*512 {
t.Errorf("(start,size) = (%d,%d), want (%d,%d)",
pd.start, pd.size, 2*512, 4*512)
}
expectedEnd := int64((2+4-1) * 512)
if pd.end != expectedEnd {
t.Errorf("pd.end = %d, want %d", pd.end, expectedEnd)
}
})
t.Run("single", func(t *testing.T) {
// restrict to explicit disk
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