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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 0, fs.ToErrno(err)
}
newOff := f.contentEnc.CipherSizeToPlainSize(uint64(newCipherOff))
return newOff, 0
}
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