// Open a varchar structure in the given blockfile with the given offset // as the control block. This function will confirm that the control // block is indeed a properly formated control block. func OpenVarchar(bf *fmap.BlockFile, a uint64) (v *Varchar, err error) { v = &Varchar{bf: bf, a: a, blkSize: bf.BlockSize()} var ptOff uint64 var szOff uint64 err = v.bf.Do(v.a, 1, func(bytes []byte) error { ctrl := asCtrl(bytes) if ctrl.flags&consts.VARCHAR_CTRL == 0 { return errors.Errorf("Expected a Varchar control block") } ptOff = ctrl.posTree szOff = ctrl.sizeTree return nil }) if err != nil { return nil, err } v.posTree, err = OpenAt(bf, ptOff) if err != nil { return nil, err } v.sizeTree, err = OpenAt(bf, szOff) if err != nil { return nil, err } return v, nil }
// Create a new varchar structure. This takes a blockfile and an offset // of an allocated block. The block becomes the control block for the // varchar file (storing the free list for the allocator). It is // important for the parent structure to track the location of this // control block. func NewVarchar(bf *fmap.BlockFile, a uint64) (v *Varchar, err error) { ptOff, err := bf.Allocate() if err != nil { return nil, err } posTree, err := NewAt(bf, ptOff, 8, 0) if err != nil { return nil, err } szOff, err := bf.Allocate() if err != nil { return nil, err } sizeTree, err := NewAt(bf, szOff, 4, 8) if err != nil { return nil, err } v = &Varchar{ bf: bf, posTree: posTree, sizeTree: sizeTree, a: a, blkSize: bf.BlockSize(), } err = v.bf.Do(v.a, 1, func(bytes []byte) error { ctrl := asCtrl(bytes) ctrl.Init(ptOff, szOff) return nil }) if err != nil { return nil, err } return v, nil }