4 files changed, 204 insertions, 6 deletions
diff --git a/pkg/sentry/fsimpl/fuse/BUILD b/pkg/sentry/fsimpl/fuse/BUILD
index 53a4f3012..d1671e576 100644
--- a/pkg/sentry/fsimpl/fuse/BUILD
+++ b/pkg/sentry/fsimpl/fuse/BUILD
@@ -31,6 +31,7 @@ go_library(
     srcs = [
         "connection.go",
         "dev.go",
+        "file.go",
         "fusefs.go",
         "init.go",
         "inode_refs.go",
diff --git a/pkg/sentry/fsimpl/fuse/connection.go b/pkg/sentry/fsimpl/fuse/connection.go
index 6df2728ab..7d3c30116 100644
--- a/pkg/sentry/fsimpl/fuse/connection.go
+++ b/pkg/sentry/fsimpl/fuse/connection.go
@@ -78,8 +78,13 @@ type Response struct {
 type connection struct {
 	fd *DeviceFD
 
+	// mu protect access to struct memebers.
+	mu sync.Mutex
+
+	// attributeVersion is the version of connection's attributes.
+	attributeVersion uint64
+
 	// The following FUSE_INIT flags are currently unsupported by this implementation:
-	// - FUSE_ATOMIC_O_TRUNC: requires open(..., O_TRUNC)
 	// - FUSE_EXPORT_SUPPORT
 	// - FUSE_HANDLE_KILLPRIV
 	// - FUSE_POSIX_LOCKS: requires POSIX locks
@@ -113,6 +118,11 @@ type connection struct {
 	// TODO(gvisor.dev/issue/3185): abort all queued requests.
 	aborted bool
 
+	// atomicOTrunc is true when FUSE does not send a separate SETATTR request
+	// before open with O_TRUNC flag.
+	// Negotiated and only set in INIT.
+	atomicOTrunc bool
+
 	// connInitError if FUSE_INIT encountered error (major version mismatch).
 	// Only set in INIT.
 	connInitError bool
@@ -189,6 +199,10 @@ type connection struct {
 	// dontMask if filestestem does not apply umask to creation modes.
 	// Negotiated in INIT.
 	dontMask bool
+
+	// noOpen if FUSE server doesn't support open operation.
+	// This flag only influence performance, not correctness of the program.
+	noOpen bool
 }
 
 // newFUSEConnection creates a FUSE connection to fd.
diff --git a/pkg/sentry/fsimpl/fuse/file.go b/pkg/sentry/fsimpl/fuse/file.go
new file mode 100644
index 000000000..ab60ab714
--- /dev/null
+++ b/pkg/sentry/fsimpl/fuse/file.go
@@ -0,0 +1,96 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fuse
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// fileDescription implements vfs.FileDescriptionImpl for fuse.
+type fileDescription struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+	vfs.NoLockFD
+
+	// the file handle used in userspace.
+	Fh uint64
+
+	// Nonseekable is indicate cannot perform seek on a file.
+	Nonseekable bool
+
+	// DirectIO suggest fuse to use direct io operation.
+	DirectIO bool
+
+	// OpenFlag is the flag returned by open.
+	OpenFlag uint32
+}
+
+func (fd *fileDescription) dentry() *kernfs.Dentry {
+	return fd.vfsfd.Dentry().Impl().(*kernfs.Dentry)
+}
+
+func (fd *fileDescription) inode() *inode {
+	return fd.dentry().Inode().(*inode)
+}
+
+func (fd *fileDescription) filesystem() *vfs.Filesystem {
+	return fd.vfsfd.VirtualDentry().Mount().Filesystem()
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *fileDescription) Release(ctx context.Context) {}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return 0, nil
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *fileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	return 0, nil
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *fileDescription) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return 0, nil
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *fileDescription) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	return 0, nil
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *fileDescription) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	return 0, nil
+}
+
+// Stat implements FileDescriptionImpl.Stat.
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	fs := fd.filesystem()
+	inode := fd.inode()
+	return inode.Stat(ctx, fs, opts)
+}
+
+// SetStat implements FileDescriptionImpl.SetStat.
+func (fd *fileDescription) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
+	return nil
+}
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index cee5acb3f..b5f05b80b 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -17,6 +17,7 @@ package fuse
 
 import (
 	"strconv"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -212,6 +213,18 @@ type inode struct {
 
 	// the owning filesystem. fs is immutable.
 	fs *filesystem
+
+	// size of the file.
+	size uint64
+
+	// attributeVersion is the version of inode's attributes.
+	attributeVersion uint64
+
+	// attributeTime is the remaining vaild time of attributes.
+	attributeTime uint64
+
+	// version of the inode.
+	version uint64
 }
 
 func (fs *filesystem) newRootInode(creds *auth.Credentials, mode linux.FileMode) *kernfs.Dentry {
@@ -237,13 +250,87 @@ func (fs *filesystem) newInode(nodeID uint64, attr linux.FUSEAttr) *kernfs.Dentr
 
 // Open implements kernfs.Inode.Open.
 func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), vfsd, &i.OrderedChildren, &i.locks, &opts, kernfs.GenericDirectoryFDOptions{
-		SeekEnd: kernfs.SeekEndStaticEntries,
-	})
-	if err != nil {
+	isDir := i.InodeAttrs.Mode().IsDir()
+	// return error if specified to open directory but inode is not a directory.
+	if !isDir && opts.Mode.IsDir() {
+		return nil, syserror.ENOTDIR
+	}
+	if opts.Flags&linux.O_LARGEFILE == 0 && atomic.LoadUint64(&i.size) > linux.MAX_NON_LFS {
+		return nil, syserror.EOVERFLOW
+	}
+
+	// FOPEN_KEEP_CACHE is the defualt flag for noOpen.
+	fd := fileDescription{OpenFlag: linux.FOPEN_KEEP_CACHE}
+	// Only send open request when FUSE server support open or is opening a directory.
+	if !i.fs.conn.noOpen || isDir {
+		kernelTask := kernel.TaskFromContext(ctx)
+		if kernelTask == nil {
+			log.Warningf("fusefs.Inode.Open: couldn't get kernel task from context")
+			return nil, syserror.EINVAL
+		}
+
+		var opcode linux.FUSEOpcode
+		if isDir {
+			opcode = linux.FUSE_OPENDIR
+		} else {
+			opcode = linux.FUSE_OPEN
+		}
+		in := linux.FUSEOpenIn{Flags: opts.Flags & ^uint32(linux.O_CREAT|linux.O_EXCL|linux.O_NOCTTY)}
+		if !i.fs.conn.atomicOTrunc {
+			in.Flags &= ^uint32(linux.O_TRUNC)
+		}
+		req, err := i.fs.conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(kernelTask.ThreadID()), i.NodeID, opcode, &in)
+		if err != nil {
+			return nil, err
+		}
+
+		res, err := i.fs.conn.Call(kernelTask, req)
+		if err != nil {
+			return nil, err
+		}
+		if err := res.Error(); err == syserror.ENOSYS && !isDir {
+			i.fs.conn.noOpen = true
+		} else if err != nil {
+			return nil, err
+		} else {
+			out := linux.FUSEOpenOut{}
+			if err := res.UnmarshalPayload(&out); err != nil {
+				return nil, err
+			}
+			fd.OpenFlag = out.OpenFlag
+			fd.Fh = out.Fh
+		}
+	}
+
+	if isDir {
+		fd.OpenFlag &= ^uint32(linux.FOPEN_DIRECT_IO)
+	}
+
+	// TODO(gvisor.dev/issue/3234): invalidate mmap after implemented it for FUSE Inode
+	fd.DirectIO = fd.OpenFlag&linux.FOPEN_DIRECT_IO != 0
+	fdOptions := &vfs.FileDescriptionOptions{}
+	if fd.OpenFlag&linux.FOPEN_NONSEEKABLE != 0 {
+		fdOptions.DenyPRead = true
+		fdOptions.DenyPWrite = true
+		fd.Nonseekable = true
+	}
+
+	// If we don't send SETATTR before open (which is indicated by atomicOTrunc)
+	// and O_TRUNC is set, update the inode's version number and clean existing data
+	// by setting the file size to 0.
+	if i.fs.conn.atomicOTrunc && opts.Flags&linux.O_TRUNC != 0 {
+		i.fs.conn.mu.Lock()
+		i.fs.conn.attributeVersion++
+		i.attributeVersion = i.fs.conn.attributeVersion
+		atomic.StoreUint64(&i.size, 0)
+		i.fs.conn.mu.Unlock()
+		i.attributeTime = 0
+	}
+
+	if err := fd.vfsfd.Init(&fd, opts.Flags, rp.Mount(), vfsd, fdOptions); err != nil {
 		return nil, err
 	}
-	return fd.VFSFileDescription(), nil
+	return &fd.vfsfd, nil
 }
 
 // Lookup implements kernfs.Inode.Lookup.