Implement FUSE_WRITE

This commit adds basic write(2) support for FUSE.

5 files changed, 219 insertions, 3 deletions

diff --git a/pkg/sentry/fsimpl/fuse/connection.go b/pkg/sentry/fsimpl/fuse/connection.go
index 5f20483b7..b3f981459 100644
--- a/pkg/sentry/fsimpl/fuse/connection.go
+++ b/pkg/sentry/fsimpl/fuse/connection.go
@@ -64,6 +64,10 @@ type Request struct {
 	id   linux.FUSEOpID
 	hdr  *linux.FUSEHeaderIn
 	data []byte
+
+	// payload for this request: extra bytes to write after
+	// the data slice. Used by FUSE_WRITE.
+	payload []byte
 }
 
 // Response represents an actual response from the server, including the
diff --git a/pkg/sentry/fsimpl/fuse/dev.go b/pkg/sentry/fsimpl/fuse/dev.go
index c53a38021..6022593d6 100644
--- a/pkg/sentry/fsimpl/fuse/dev.go
+++ b/pkg/sentry/fsimpl/fuse/dev.go
@@ -152,7 +152,7 @@ func (fd *DeviceFD) readLocked(ctx context.Context, dst usermem.IOSequence, opts
 	for !fd.queue.Empty() {
 		req = fd.queue.Front()
 
-		if int64(req.hdr.Len) <= dst.NumBytes() {
+		if int64(req.hdr.Len)+int64(len(req.payload)) <= dst.NumBytes() {
 			break
 		}
 
@@ -191,6 +191,17 @@ func (fd *DeviceFD) readLocked(ctx context.Context, dst usermem.IOSequence, opts
 		return 0, syserror.EIO
 	}
 
+	if req.hdr.Opcode == linux.FUSE_WRITE {
+		written, err := dst.DropFirst(n).CopyOut(ctx, req.payload)
+		if err != nil {
+			return 0, err
+		}
+		if written != len(req.payload) {
+			return 0, syserror.EIO
+		}
+		n += int(written)
+	}
+
 	// Fully done with this req, remove it from the queue.
 	fd.queue.Remove(req)
 	if req.hdr.Opcode == linux.FUSE_RELEASE {
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index cfae9ed0d..8cf13dcb6 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -18,6 +18,7 @@ package fuse
 import (
 	"math"
 	"strconv"
+	"sync"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -228,13 +229,18 @@ type inode struct {
 	kernfs.InodeNotSymlink
 	kernfs.OrderedChildren
 
-	NodeID uint64
 	dentry kernfs.Dentry
-	locks  vfs.FileLocks
 
 	// the owning filesystem. fs is immutable.
 	fs *filesystem
 
+	// metaDataMu protects the metadata of this inode.
+	metadataMu sync.Mutex
+
+	NodeID uint64
+
+	locks vfs.FileLocks
+
 	// size of the file.
 	size uint64
 
diff --git a/pkg/sentry/fsimpl/fuse/read_write.go b/pkg/sentry/fsimpl/fuse/read_write.go
index 4ef8531dc..22a018e5e 100644
--- a/pkg/sentry/fsimpl/fuse/read_write.go
+++ b/pkg/sentry/fsimpl/fuse/read_write.go
@@ -150,3 +150,93 @@ func (fs *filesystem) ReadCallback(ctx context.Context, fd *regularFileFD, off u
 		fs.conn.mu.Unlock()
 	}
 }
+
+// Write sends FUSE_WRITE requests and return the bytes
+// written according to the response.
+//
+// Preconditions: len(data) == size.
+func (fs *filesystem) Write(ctx context.Context, fd *regularFileFD, off uint64, size uint32, data []byte) (uint32, error) {
+	t := kernel.TaskFromContext(ctx)
+	if t == nil {
+		log.Warningf("fusefs.Read: couldn't get kernel task from context")
+		return 0, syserror.EINVAL
+	}
+
+	// One request cannnot exceed either maxWrite or maxPages.
+	maxWrite := uint32(fs.conn.maxPages) << usermem.PageShift
+	if maxWrite > fs.conn.maxWrite {
+		maxWrite = fs.conn.maxWrite
+	}
+
+	// Reuse the same struct for unmarshalling to avoid unnecessary memory allocation.
+	in := linux.FUSEWriteIn{
+		Fh: fd.Fh,
+		// TODO(gvisor.dev/issue/3245): file lock
+		LockOwner: 0,
+		// TODO(gvisor.dev/issue/3245): |= linux.FUSE_READ_LOCKOWNER
+		// TODO(gvisor.dev/issue/3237): |= linux.FUSE_WRITE_CACHE (not added yet)
+		WriteFlags: 0,
+		Flags:      fd.statusFlags(),
+	}
+
+	var written uint32
+
+	// This loop is intended for fragmented write where the bytes to write is
+	// larger than either the maxWrite or maxPages or when bigWrites is false.
+	// Unless a small value for max_write is explicitly used, this loop
+	// is expected to execute only once for the majority of the writes.
+	for written < size {
+		toWrite := size - written
+
+		// Limit the write size to one page.
+		// Note that the bigWrites flag is obsolete,
+		// latest libfuse always sets it on.
+		if !fs.conn.bigWrites && toWrite > usermem.PageSize {
+			toWrite = usermem.PageSize
+		}
+
+		// Limit the write size to maxWrite.
+		if toWrite > maxWrite {
+			toWrite = maxWrite
+		}
+
+		in.Offset = off + uint64(written)
+		in.Size = toWrite
+
+		req, err := fs.conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(t.ThreadID()), fd.inode().NodeID, linux.FUSE_WRITE, &in)
+		if err != nil {
+			return 0, err
+		}
+
+		req.payload = data[written : written+toWrite]
+
+		// TODO(gvisor.dev/issue/3247): support async write.
+
+		res, err := fs.conn.Call(t, req)
+		if err != nil {
+			return 0, err
+		}
+		if err := res.Error(); err != nil {
+			return 0, err
+		}
+
+		out := linux.FUSEWriteOut{}
+		if err := res.UnmarshalPayload(&out); err != nil {
+			return 0, err
+		}
+
+		// Write more than requested? EIO.
+		if out.Size > toWrite {
+			return 0, syserror.EIO
+		}
+
+		written += out.Size
+
+		// Break if short write. Not necessarily an error.
+		if out.Size != toWrite {
+			break
+		}
+	}
+
+	return written, nil
+}
diff --git a/pkg/sentry/fsimpl/fuse/regular_file.go b/pkg/sentry/fsimpl/fuse/regular_file.go
index 37ce4e268..193e77392 100644
--- a/pkg/sentry/fsimpl/fuse/regular_file.go
+++ b/pkg/sentry/fsimpl/fuse/regular_file.go
@@ -123,3 +123,108 @@ func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts
 	fd.offMu.Unlock()
 	return n, err
 }
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	n, _, err := fd.pwrite(ctx, src, offset, opts)
+	return n, err
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *regularFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	fd.offMu.Lock()
+	n, off, err := fd.pwrite(ctx, src, fd.off, opts)
+	fd.off = off
+	fd.offMu.Unlock()
+	return n, err
+}
+
+// pwrite returns the number of bytes written, final offset and error. The
+// final offset should be ignored by PWrite.
+func (fd *regularFileFD) pwrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (written, finalOff int64, err error) {
+	if offset < 0 {
+		return 0, offset, syserror.EINVAL
+	}
+
+	// Check that flags are supported.
+	//
+	// TODO(gvisor.dev/issue/2601): Support select preadv2 flags.
+	if opts.Flags&^linux.RWF_HIPRI != 0 {
+		return 0, offset, syserror.EOPNOTSUPP
+	}
+
+	inode := fd.inode()
+	inode.metadataMu.Lock()
+	defer inode.metadataMu.Unlock()
+
+	// If the file is opened with O_APPEND, update offset to file size.
+	// Note: since our Open() implements the interface of kernfs,
+	// and kernfs currently does not support O_APPEND, this will never
+	// be true before we switch out from kernfs.
+	if fd.vfsfd.StatusFlags()&linux.O_APPEND != 0 {
+		// Locking inode.metadataMu is sufficient for reading size
+		offset = int64(inode.size)
+	}
+
+	srclen := src.NumBytes()
+
+	if srclen > math.MaxUint32 {
+		// FUSE only supports uint32 for size.
+		// Overflow.
+		return 0, offset, syserror.EINVAL
+	}
+	if end := offset + srclen; end < offset {
+		// Overflow.
+		return 0, offset, syserror.EINVAL
+	}
+
+	srclen, err = vfs.CheckLimit(ctx, offset, srclen)
+	if err != nil {
+		return 0, offset, err
+	}
+
+	if srclen == 0 {
+		// Return before causing any side effects.
+		return 0, offset, nil
+	}
+
+	src = src.TakeFirst64(srclen)
+
+	// TODO(gvisor.dev/issue/3237): Add cache support:
+	// buffer cache. Ideally we write from src to our buffer cache first.
+	// The slice passed to fs.Write() should be a slice from buffer cache.
+	data := make([]byte, srclen)
+	// Reason for making a copy here: connection.Call() blocks on kerneltask,
+	// which in turn acquires mm.activeMu lock. Functions like CopyInTo() will
+	// attemp to acquire the mm.activeMu lock as well -> deadlock.
+	// We must finish reading from the userspace memory before
+	// t.Block() deactivates it.
+	cp, err := src.CopyIn(ctx, data)
+	if err != nil {
+		return 0, offset, err
+	}
+	if int64(cp) != srclen {
+		return 0, offset, syserror.EIO
+	}
+
+	n, err := fd.inode().fs.Write(ctx, fd, uint64(offset), uint32(srclen), data)
+	if err != nil {
+		return 0, offset, err
+	}
+
+	if n == 0 {
+		// We have checked srclen != 0 previously.
+		// If err == nil, then it's a short write and we return EIO.
+		return 0, offset, syserror.EIO
+	}
+
+	written = int64(n)
+	finalOff = offset + written
+
+	if finalOff > int64(inode.size) {
+		atomic.StoreUint64(&inode.size, uint64(finalOff))
+		atomic.AddUint64(&inode.fs.conn.attributeVersion, 1)
+	}
+
+	return
+}