package fusefrontend // Helper functions for sparse files (files with holes) import ( "context" "syscall" "github.com/hanwen/go-fuse/v2/fs" "github.com/rfjakob/gocryptfs/internal/tlog" ) // Will a write to plaintext offset "targetOff" create a file hole in the // ciphertext? If yes, zero-pad the last ciphertext block. func (f *File) writePadHole(targetOff int64) syscall.Errno { // Get the current file size. fi, err := f.fd.Stat() if err != nil { tlog.Warn.Printf("checkAndPadHole: Fstat failed: %v", err) return fs.ToErrno(err) } plainSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size())) // Appending a single byte to the file (equivalent to writing to // offset=plainSize) would write to "nextBlock". nextBlock := f.contentEnc.PlainOffToBlockNo(plainSize) // targetBlock is the block the user wants to write to. targetBlock := f.contentEnc.PlainOffToBlockNo(uint64(targetOff)) // The write goes into an existing block or (if the last block was full) // starts a new one directly after the last block. Nothing to do. if targetBlock <= nextBlock { return 0 } // The write goes past the next block. nextBlock has // to be zero-padded to the block boundary and (at least) nextBlock+1 // will contain a file hole in the ciphertext. errno := f.zeroPad(plainSize) if errno != 0 { return errno } return 0 } // Zero-pad the file of size plainSize to the next block boundary. This is a no-op // if the file is already block-aligned. func (f *File) zeroPad(plainSize uint64) syscall.Errno { lastBlockLen := plainSize % f.contentEnc.PlainBS() if lastBlockLen == 0 { // Already block-aligned return 0 } missing := f.contentEnc.PlainBS() - lastBlockLen pad := make([]byte, missing) tlog.Debug.Printf("zeroPad: Writing %d bytes\n", missing) _, errno := f.doWrite(pad, int64(plainSize)) return errno } // Lseek - FUSE call. func (f *File) Lseek(ctx context.Context, off uint64, whence uint32) (uint64, syscall.Errno) { cipherOff := f.rootNode.contentEnc.PlainSizeToCipherSize(off) newCipherOff, err := syscall.Seek(f.intFd(), int64(cipherOff), int(whence)) if err != nil { return uint64(newCipherOff), fs.ToErrno(err) } newOff := f.contentEnc.CipherSizeToPlainSize(uint64(newCipherOff)) return newOff, 0 }