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Diffstat (limited to 'internal/fusefrontend/file_holes.go')
-rw-r--r--internal/fusefrontend/file_holes.go68
1 files changed, 68 insertions, 0 deletions
diff --git a/internal/fusefrontend/file_holes.go b/internal/fusefrontend/file_holes.go
new file mode 100644
index 0000000..85792f9
--- /dev/null
+++ b/internal/fusefrontend/file_holes.go
@@ -0,0 +1,68 @@
+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
+}