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-rw-r--r--internal/fusefrontend/file_holes.go27
1 files changed, 25 insertions, 2 deletions
diff --git a/internal/fusefrontend/file_holes.go b/internal/fusefrontend/file_holes.go
index 3725f56..c9f7aa6 100644
--- a/internal/fusefrontend/file_holes.go
+++ b/internal/fusefrontend/file_holes.go
@@ -64,6 +64,29 @@ func (f *File) SeekData(oldOffset int64) (int64, error) {
return 0, syscall.EOPNOTSUPP
}
const SEEK_DATA = 3
- fd := f.intFd()
- return syscall.Seek(fd, oldOffset, SEEK_DATA)
+
+ // Convert plaintext offset to ciphertext offset and round down to the
+ // start of the current block. File holes smaller than a full block will
+ // be ignored.
+ blockNo := f.contentEnc.PlainOffToBlockNo(uint64(oldOffset))
+ oldCipherOff := int64(f.contentEnc.BlockNoToCipherOff(blockNo))
+
+ // Determine the next data offset. If the old offset points to (or beyond)
+ // the end of the file, the Seek syscall fails with syscall.ENXIO.
+ newCipherOff, err := syscall.Seek(f.intFd(), oldCipherOff, SEEK_DATA)
+ if err != nil {
+ return 0, err
+ }
+
+ // Convert ciphertext offset back to plaintext offset. At this point,
+ // newCipherOff should always be >= contentenc.HeaderLen. Round down,
+ // but ensure that the result is never smaller than the initial offset
+ // (to avoid endless loops).
+ blockNo = f.contentEnc.CipherOffToBlockNo(uint64(newCipherOff))
+ newOffset := int64(f.contentEnc.BlockNoToPlainOff(blockNo))
+ if newOffset < oldOffset {
+ newOffset = oldOffset
+ }
+
+ return newOffset, nil
}