1 files changed, 138 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/mqfs/mqfs.go b/pkg/sentry/fsimpl/mqfs/mqfs.go
new file mode 100644
index 000000000..c2b53c9d0
--- /dev/null
+++ b/pkg/sentry/fsimpl/mqfs/mqfs.go
@@ -0,0 +1,138 @@
+// 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/kernel/ipc"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/mq"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+const (
+	// Name is the user-visible filesystem name.
+	Name                     = "mqueue"
+	defaultMaxCachedDentries = uint64(1000)
+)
+
+// FilesystemType implements vfs.FilesystemType.
+//
+// +stateify savable
+type FilesystemType struct{}
+
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
+// 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) {
+	// mqfs is initialized only once per ipc namespace. Each ipc namespace has
+	// a POSIX message registry with a root dentry, filesystem, and a
+	// disconnected mount. We want the fs to be consistent for all processes in
+	// the same ipc namespace, so instead of creating a new fs and root dentry,
+	// we retreive them using IPCNamespace.PosixQueues and use them.
+
+	i := ipcNamespaceFromContext(ctx)
+	if i == nil {
+		return nil, nil, fmt.Errorf("mqfs.FilesystemType.GetFilesystem: ipc namespace doesn't exist")
+	}
+	defer i.DecRef(ctx)
+
+	registry := i.PosixQueues()
+	if registry == nil {
+		return nil, nil, fmt.Errorf("mqfs.FilesystemType.GetFilesystem: ipc namespace doesn't have a POSIX registry")
+	}
+	impl := registry.Impl().(*RegistryImpl)
+
+	maxCachedDentries, err := maxCachedDentries(ctx, vfs.GenericParseMountOptions(opts.Data))
+	if err != nil {
+		return nil, nil, err
+	}
+	impl.fs.MaxCachedDentries = maxCachedDentries
+
+	impl.fs.VFSFilesystem().IncRef()
+	return impl.fs.VFSFilesystem(), impl.root.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
+
+	// root is the filesystem's root dentry. Since we take a reference on it in
+	// GetFilesystem, we should release it when the fs is released.
+	root *kernfs.Dentry
+}
+
+// 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)
+}
+
+// ipcNamespace defines functions we need from kernel.IPCNamespace. We redefine
+// ipcNamespace along with ipcNamespaceFromContext to avoid circular dependency
+// with package sentry/kernel.
+type ipcNamespace interface {
+	// PosixQueues returns a POSIX message queue registry.
+	PosixQueues() *mq.Registry
+
+	// DecRef decrements ipcNamespace's number of references.
+	DecRef(ctx context.Context)
+}
+
+// ipcNamespaceFromContext returns the IPC namespace in which ctx is executing.
+// Copied from package sentry/kernel.
+func ipcNamespaceFromContext(ctx context.Context) ipcNamespace {
+	if v := ctx.Value(ipc.CtxIPCNamespace); v != nil {
+		return v.(ipcNamespace)
+	}
+	return nil
+}