Implement vfs.FilesystemType and kernfs.Filesystem for mqfs.

Updates #136

pkg/sentry/fsimpl/mqfs/BUILD

@@ -17,6 +17,7 @@ go_template_instance(
 go_library(
     name = "mqfs",
     srcs = [
+        "mqfs.go",
         "inodes.go",
         "root_inode_refs.go",
     ],

pkg/sentry/fsimpl/mqfs/mqfs.go

@@ -0,0 +1,107 @@
+// Copyright 2021 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 mqfs provides a filesystem implementation to back POSIX message
+// queues.
+package mqfs
+
+import (
+	"fmt"
+	"strconv"
+
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/errors/linuxerr"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+const (
+	fsName                   = "mqueue"
+	defaultMaxCachedDentries = uint64(1000)
+)
+
+// FilesystemType implements vfs.FilesystemType.
+//
+// +stateify savable
+type FilesystemType struct{}
+
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return fsName
+}
+
+// Release implements vfs.FilesystemType.Release.
+func (FilesystemType) Release(ctx context.Context) {}
+
+// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
+func (ft FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	devMinor, err := vfsObj.GetAnonBlockDevMinor()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	maxCachedDentries, err := maxCachedDentries(ctx, vfs.GenericParseMountOptions(opts.Data))
+	if err != nil {
+		return nil, nil, err
+	}
+
+	fs := &filesystem{
+		devMinor: devMinor,
+		Filesystem: kernfs.Filesystem{
+			MaxCachedDentries: maxCachedDentries,
+		},
+	}
+	fs.VFSFilesystem().Init(vfsObj, &ft, fs)
+
+	var dentry kernfs.Dentry
+	dentry.InitRoot(&fs.Filesystem, fs.newRootInode(ctx, creds))
+
+	return fs.VFSFilesystem(), dentry.VFSDentry(), nil
+}
+
+// maxCachedDentries checks mopts for dentry_cache_limit. If a value is
+// specified, parse it into uint64 and return it. Otherwise, return the default
+// value. An error is returned if a value is found but can't be parsed.
+func maxCachedDentries(ctx context.Context, mopts map[string]string) (_ uint64, err error) {
+	max := defaultMaxCachedDentries
+	if str, ok := mopts["dentry_cache_limit"]; ok {
+		delete(mopts, "dentry_cache_limit")
+		max, err = strconv.ParseUint(str, 10, 64)
+		if err != nil {
+			ctx.Warningf("mqfs.FilesystemType.GetFilesystem: invalid dentry cache limit: dentry_cache_limit=%s", str)
+			return 0, linuxerr.EINVAL
+		}
+	}
+	return max, nil
+}
+
+// filesystem implements kernfs.Filesystem.
+//
+// +stateify savable
+type filesystem struct {
+	kernfs.Filesystem
+	devMinor uint32
+}
+
+// Release implements vfs.FilesystemImpl.Release.
+func (fs *filesystem) Release(ctx context.Context) {
+	fs.Filesystem.VFSFilesystem().VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
+	fs.Filesystem.Release(ctx)
+}
+
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return fmt.Sprintf("dentry_cache_limit=%d", fs.MaxCachedDentries)
+}