// reload reads back info about b from b.filename.
// b.filename should be set.
func (b *Buffer) reload() error {
stat, err := os.Stat(b.filename)
if err != nil {
return err
}
fsize := uint64(stat.Size())
b.capacity = fsize - metadata
f, err := os.OpenFile(b.filename, os.O_RDWR, 0600)
if err != nil {
return err
}
data, err := syscall.Mmap(
int(f.Fd()), 0, int(fsize),
syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED,
)
if err != nil {
return err
}
b.data = data
off := int(b.capacity)
b.first = binary.GetLittleEndianUint64(b.data, off)
b.last = binary.GetLittleEndianUint64(b.data, off+8)
b.nextSeq = binary.GetLittleEndianUint64(b.data, off+16)
b.biggest = binary.GetLittleEndianUint32(b.data, off+24)
b.length = binary.GetLittleEndianUint64(b.data, off+28)
return nil
}
// seq returns the record sequence encoded in the frame.
// It returns 0 if not enough of the frame has been read
// to determine the encoded sequence.
func (f frame) seq() uint64 {
if len(f) < total {
return 0
}
return binary.GetLittleEndianUint64(f, size)
}