Implement mqfs.rootInode.

rootInode represents the root inode for mqueue filesystem (/dev/mqueue).

Updates #136

pkg/abi/linux/fs.go

@@ -23,6 +23,7 @@ const (
 	DEVPTS_SUPER_MAGIC    = 0x00001cd1
 	EXT_SUPER_MAGIC       = 0xef53
 	FUSE_SUPER_MAGIC      = 0x65735546
+	MQUEUE_MAGIC          = 0x19800202
 	OVERLAYFS_SUPER_MAGIC = 0x794c7630
 	PIPEFS_MAGIC          = 0x50495045
 	PROC_SUPER_MAGIC      = 0x9fa0

pkg/sentry/fsimpl/mqfs/BUILD

@@ -0,0 +1,33 @@
+load("//tools:defs.bzl", "go_library")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
+
+package(licenses = ["notice"])
+
+go_template_instance(
+    name = "root_inode_refs",
+    out = "root_inode_refs.go",
+    package = "mqfs",
+    prefix = "rootInode",
+    template = "//pkg/refsvfs2:refs_template",
+    types = {
+        "T": "rootInode",
+    },
+)
+
+go_library(
+    name = "mqfs",
+    srcs = [
+        "inodes.go",
+        "root_inode_refs.go",
+    ],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/context",
+        "//pkg/errors/linuxerr",
+        "//pkg/refsvfs2",
+        "//pkg/sentry/fsimpl/kernfs",
+        "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/vfs",
+    ],
+)

pkg/sentry/fsimpl/mqfs/inodes.go

@@ -0,0 +1,91 @@
+// 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
+
+import (
+	"bytes"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"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"
+)
+
+// rootInode represents inode for filesystem's root directory (/dev/mqueue).
+//
+// +stateify savable
+type rootInode struct {
+	rootInodeRefs
+	kernfs.InodeAlwaysValid
+	kernfs.InodeAttrs
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotSymlink
+	kernfs.InodeTemporary
+	kernfs.OrderedChildren
+	implStatFS
+
+	locks vfs.FileLocks
+}
+
+var _ kernfs.Inode = (*rootInode)(nil)
+
+// newRootInode returns a new, initialized rootInode.
+func (fs *filesystem) newRootInode(ctx context.Context, creds *auth.Credentials) kernfs.Inode {
+	inode := &rootInode{}
+	inode.InodeAttrs.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), linux.ModeDirectory|linux.FileMode(0555))
+	inode.OrderedChildren.Init(kernfs.OrderedChildrenOptions{Writable: true})
+	inode.InitRefs()
+	return inode
+}
+
+// Open implements kernfs.Inode.Open.
+func (i *rootInode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), d, &i.OrderedChildren, &i.locks, &opts, kernfs.GenericDirectoryFDOptions{
+		SeekEnd: kernfs.SeekEndZero,
+	})
+	if err != nil {
+		return nil, err
+	}
+	return fd.VFSFileDescription(), nil
+}
+
+// DecRef implements kernfs.Inode.DecRef.
+func (i *rootInode) DecRef(ctx context.Context) {
+	i.rootInodeRefs.DecRef(func() { i.Destroy(ctx) })
+}
+
+// Rename implements Inode.Rename and overrides OrderedChildren.Rename. mqueue
+// filesystem allows files to be unlinked, but not renamed.
+func (i *rootInode) Rename(ctx context.Context, oldname, newname string, child, dstDir kernfs.Inode) error {
+	return linuxerr.EPERM
+}
+
+// SetStat implements kernfs.Inode.SetStat not allowing inode attributes to be changed.
+func (*rootInode) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return linuxerr.EPERM
+}
+
+// implStatFS provides an implementation of kernfs.Inode.StatFS for message
+// queues to be embedded in inodes.
+//
+// +stateify savable
+type implStatFS struct{}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.MQUEUE_MAGIC), nil
+}