1 files changed, 217 insertions, 0 deletions
diff --git a/internal/fusefrontend/file2_allocate_truncate.go b/internal/fusefrontend/file2_allocate_truncate.go
new file mode 100644
index 0000000..f799a3e
--- /dev/null
+++ b/internal/fusefrontend/file2_allocate_truncate.go
@@ -0,0 +1,217 @@
+package fusefrontend
+
+// FUSE operations Truncate and Allocate on file handles
+// i.e. ftruncate and fallocate
+
+import (
+	"log"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// Allocate - FUSE call for fallocate(2)
+//
+// mode=FALLOC_FL_KEEP_SIZE is implemented directly.
+//
+// mode=FALLOC_DEFAULT is implemented as a two-step process:
+//
+//   (1) Allocate the space using FALLOC_FL_KEEP_SIZE
+//   (2) Set the file size using ftruncate (via truncateGrowFile)
+//
+// This allows us to reuse the file grow mechanics from Truncate as they are
+// complicated and hard to get right.
+//
+// Other modes (hole punching, zeroing) are not supported.
+func (f *File2) Allocate(off uint64, sz uint64, mode uint32) fuse.Status {
+	if mode != FALLOC_DEFAULT && mode != FALLOC_FL_KEEP_SIZE {
+		f := func() {
+			tlog.Info.Printf("fallocate: only mode 0 (default) and 1 (keep size) are supported")
+		}
+		allocateWarnOnce.Do(f)
+		return fuse.Status(syscall.EOPNOTSUPP)
+	}
+
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+	if f.released {
+		return fuse.EBADF
+	}
+	f.fileTableEntry.ContentLock.Lock()
+	defer f.fileTableEntry.ContentLock.Unlock()
+
+	blocks := f.contentEnc.ExplodePlainRange(off, sz)
+	firstBlock := blocks[0]
+	lastBlock := blocks[len(blocks)-1]
+
+	// Step (1): Allocate the space the user wants using FALLOC_FL_KEEP_SIZE.
+	// This will fill file holes and/or allocate additional space past the end of
+	// the file.
+	cipherOff := firstBlock.BlockCipherOff()
+	cipherSz := lastBlock.BlockCipherOff() - cipherOff +
+		f.contentEnc.BlockOverhead() + lastBlock.Skip + lastBlock.Length
+	err := syscallcompat.Fallocate(f.intFd(), FALLOC_FL_KEEP_SIZE, int64(cipherOff), int64(cipherSz))
+	tlog.Debug.Printf("Allocate off=%d sz=%d mode=%x cipherOff=%d cipherSz=%d\n",
+		off, sz, mode, cipherOff, cipherSz)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	if mode == FALLOC_FL_KEEP_SIZE {
+		// The user did not want to change the apparent size. We are done.
+		return fuse.OK
+	}
+	// Step (2): Grow the apparent file size
+	// We need the old file size to determine if we are growing the file at all.
+	newPlainSz := off + sz
+	oldPlainSz, err := f.statPlainSize()
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	if newPlainSz <= oldPlainSz {
+		// The new size is smaller (or equal). Fallocate with mode = 0 never
+		// truncates a file, so we are done.
+		return fuse.OK
+	}
+	// The file grows. The space has already been allocated in (1), so what is
+	// left to do is to pad the first and last block and call truncate.
+	// truncateGrowFile does just that.
+	return f.truncateGrowFile(oldPlainSz, newPlainSz)
+}
+
+// Truncate - FUSE call
+func (f *File2) Truncate(newSize uint64) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+	if f.released {
+		// The file descriptor has been closed concurrently.
+		tlog.Warn.Printf("ino%d fh%d: Truncate on released file", f.qIno.Ino, f.intFd())
+		return fuse.EBADF
+	}
+	f.fileTableEntry.ContentLock.Lock()
+	defer f.fileTableEntry.ContentLock.Unlock()
+	var err error
+	// Common case first: Truncate to zero
+	if newSize == 0 {
+		err = syscall.Ftruncate(int(f.fd.Fd()), 0)
+		if err != nil {
+			tlog.Warn.Printf("ino%d fh%d: Ftruncate(fd, 0) returned error: %v", f.qIno.Ino, f.intFd(), err)
+			return fuse.ToStatus(err)
+		}
+		// Truncate to zero kills the file header
+		f.fileTableEntry.ID = nil
+		return fuse.OK
+	}
+	// We need the old file size to determine if we are growing or shrinking
+	// the file
+	oldSize, err := f.statPlainSize()
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+
+	oldB := float32(oldSize) / float32(f.contentEnc.PlainBS())
+	newB := float32(newSize) / float32(f.contentEnc.PlainBS())
+	tlog.Debug.Printf("ino%d: FUSE Truncate from %.2f to %.2f blocks (%d to %d bytes)", f.qIno.Ino, oldB, newB, oldSize, newSize)
+
+	// File size stays the same - nothing to do
+	if newSize == oldSize {
+		return fuse.OK
+	}
+	// File grows
+	if newSize > oldSize {
+		return f.truncateGrowFile(oldSize, newSize)
+	}
+
+	// File shrinks
+	blockNo := f.contentEnc.PlainOffToBlockNo(newSize)
+	cipherOff := f.contentEnc.BlockNoToCipherOff(blockNo)
+	plainOff := f.contentEnc.BlockNoToPlainOff(blockNo)
+	lastBlockLen := newSize - plainOff
+	var data []byte
+	if lastBlockLen > 0 {
+		var status fuse.Status
+		data, status = f.doRead(nil, plainOff, lastBlockLen)
+		if status != fuse.OK {
+			tlog.Warn.Printf("Truncate: shrink doRead returned error: %v", err)
+			return status
+		}
+	}
+	// Truncate down to the last complete block
+	err = syscall.Ftruncate(int(f.fd.Fd()), int64(cipherOff))
+	if err != nil {
+		tlog.Warn.Printf("Truncate: shrink Ftruncate returned error: %v", err)
+		return fuse.ToStatus(err)
+	}
+	// Append partial block
+	if lastBlockLen > 0 {
+		_, status := f.doWrite(data, int64(plainOff))
+		return status
+	}
+	return fuse.OK
+}
+
+// statPlainSize stats the file and returns the plaintext size
+func (f *File2) statPlainSize() (uint64, error) {
+	fi, err := f.fd.Stat()
+	if err != nil {
+		tlog.Warn.Printf("ino%d fh%d: statPlainSize: %v", f.qIno.Ino, f.intFd(), err)
+		return 0, err
+	}
+	cipherSz := uint64(fi.Size())
+	plainSz := uint64(f.contentEnc.CipherSizeToPlainSize(cipherSz))
+	return plainSz, nil
+}
+
+// truncateGrowFile extends a file using seeking or ftruncate performing RMW on
+// the first and last block as necessary. New blocks in the middle become
+// file holes unless they have been fallocate()'d beforehand.
+func (f *File2) truncateGrowFile(oldPlainSz uint64, newPlainSz uint64) fuse.Status {
+	if newPlainSz <= oldPlainSz {
+		log.Panicf("BUG: newSize=%d <= oldSize=%d", newPlainSz, oldPlainSz)
+	}
+	newEOFOffset := newPlainSz - 1
+	if oldPlainSz > 0 {
+		n1 := f.contentEnc.PlainOffToBlockNo(oldPlainSz - 1)
+		n2 := f.contentEnc.PlainOffToBlockNo(newEOFOffset)
+		// The file is grown within one block, no need to pad anything.
+		// Write a single zero to the last byte and let doWrite figure out the RMW.
+		if n1 == n2 {
+			buf := make([]byte, 1)
+			_, status := f.doWrite(buf, int64(newEOFOffset))
+			return status
+		}
+	}
+	// The truncate creates at least one new block.
+	//
+	// Make sure the old last block is padded to the block boundary. This call
+	// is a no-op if it is already block-aligned.
+	status := f.zeroPad(oldPlainSz)
+	if !status.Ok() {
+		return status
+	}
+	// The new size is block-aligned. In this case we can do everything ourselves
+	// and avoid the call to doWrite.
+	if newPlainSz%f.contentEnc.PlainBS() == 0 {
+		// The file was empty, so it did not have a header. Create one.
+		if oldPlainSz == 0 {
+			id, err := f.createHeader()
+			if err != nil {
+				return fuse.ToStatus(err)
+			}
+			f.fileTableEntry.ID = id
+		}
+		cSz := int64(f.contentEnc.PlainSizeToCipherSize(newPlainSz))
+		err := syscall.Ftruncate(f.intFd(), cSz)
+		if err != nil {
+			tlog.Warn.Printf("Truncate: grow Ftruncate returned error: %v", err)
+		}
+		return fuse.ToStatus(err)
+	}
+	// The new size is NOT aligned, so we need to write a partial block.
+	// Write a single zero to the last byte and let doWrite figure it out.
+	buf := make([]byte, 1)
+	_, status = f.doWrite(buf, int64(newEOFOffset))
+	return status
+}