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// 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 devpts provides a filesystem implementation that behaves like
// devpts.
package devpts
import (
"fmt"
"math"
"sort"
"strconv"
"sync"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
)
// Name is the filesystem name.
const Name = "devpts"
// FilesystemType implements vfs.FilesystemType.
type FilesystemType struct{}
// Name implements vfs.FilesystemType.Name.
func (FilesystemType) Name() string {
return Name
}
var _ vfs.FilesystemType = (*FilesystemType)(nil)
// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
// No data allowed.
if opts.Data != "" {
return nil, nil, syserror.EINVAL
}
fs, root := fstype.newFilesystem(vfsObj, creds)
return fs.VFSFilesystem(), root.VFSDentry(), nil
}
// newFilesystem creates a new devpts filesystem with root directory and ptmx
// master inode. It returns the filesystem and root Dentry.
func (fstype FilesystemType) newFilesystem(vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials) (*kernfs.Filesystem, *kernfs.Dentry) {
fs := &kernfs.Filesystem{}
fs.Init(vfsObj, fstype)
// Construct the root directory. This is always inode id 1.
root := &rootInode{
slaves: make(map[uint32]*slaveInode),
}
root.InodeAttrs.Init(creds, 1, linux.ModeDirectory|0555)
root.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
root.dentry.Init(root)
// Construct the pts master inode and dentry. Linux always uses inode
// id 2 for ptmx. See fs/devpts/inode.c:mknod_ptmx.
master := &masterInode{
root: root,
}
master.InodeAttrs.Init(creds, 2, linux.ModeCharacterDevice|0666)
master.dentry.Init(master)
// Add the master as a child of the root.
links := root.OrderedChildren.Populate(&root.dentry, map[string]*kernfs.Dentry{
"ptmx": &master.dentry,
})
root.IncLinks(links)
return fs, &root.dentry
}
// rootInode is the root directory inode for the devpts mounts.
type rootInode struct {
kernfs.AlwaysValid
kernfs.InodeAttrs
kernfs.InodeDirectoryNoNewChildren
kernfs.InodeNotSymlink
kernfs.OrderedChildren
// Keep a reference to this inode's dentry.
dentry kernfs.Dentry
// master is the master pty inode. Immutable.
master *masterInode
// root is the root directory inode for this filesystem. Immutable.
root *rootInode
// mu protects the fields below.
mu sync.Mutex
// slaves maps pty ids to slave inodes.
slaves map[uint32]*slaveInode
// nextIdx is the next pty index to use. Must be accessed atomically.
//
// TODO(b/29356795): reuse indices when ptys are closed.
nextIdx uint32
}
var _ kernfs.Inode = (*rootInode)(nil)
// allocateTerminal creates a new Terminal and installs a pts node for it.
func (i *rootInode) allocateTerminal(creds *auth.Credentials) (*Terminal, error) {
i.mu.Lock()
defer i.mu.Unlock()
if i.nextIdx == math.MaxUint32 {
return nil, syserror.ENOMEM
}
idx := i.nextIdx
i.nextIdx++
// Sanity check that slave with idx does not exist.
if _, ok := i.slaves[idx]; ok {
panic(fmt.Sprintf("pty index collision; index %d already exists", idx))
}
// Create the new terminal and slave.
t := newTerminal(idx)
slave := &slaveInode{
root: i,
t: t,
}
// Linux always uses pty index + 3 as the inode id. See
// fs/devpts/inode.c:devpts_pty_new().
slave.InodeAttrs.Init(creds, uint64(idx+3), linux.ModeCharacterDevice|0600)
slave.dentry.Init(slave)
i.slaves[idx] = slave
return t, nil
}
// masterClose is called when the master end of t is closed.
func (i *rootInode) masterClose(t *Terminal) {
i.mu.Lock()
defer i.mu.Unlock()
// Sanity check that slave with idx exists.
if _, ok := i.slaves[t.n]; !ok {
panic(fmt.Sprintf("pty with index %d does not exist", t.n))
}
delete(i.slaves, t.n)
}
// Open implements kernfs.Inode.Open.
func (i *rootInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
fd := &kernfs.GenericDirectoryFD{}
fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
return fd.VFSFileDescription(), nil
}
// Lookup implements kernfs.Inode.Lookup.
func (i *rootInode) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
idx, err := strconv.ParseUint(name, 10, 32)
if err != nil {
return nil, syserror.ENOENT
}
i.mu.Lock()
defer i.mu.Unlock()
if si, ok := i.slaves[uint32(idx)]; ok {
si.dentry.IncRef()
return si.dentry.VFSDentry(), nil
}
return nil, syserror.ENOENT
}
// IterDirents implements kernfs.Inode.IterDirents.
func (i *rootInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, offset, relOffset int64) (int64, error) {
i.mu.Lock()
defer i.mu.Unlock()
ids := make([]int, 0, len(i.slaves))
for id := range i.slaves {
ids = append(ids, int(id))
}
sort.Ints(ids)
for _, id := range ids[relOffset:] {
dirent := vfs.Dirent{
Name: strconv.FormatUint(uint64(id), 10),
Type: linux.DT_CHR,
Ino: i.slaves[uint32(id)].InodeAttrs.Ino(),
NextOff: offset + 1,
}
if err := cb.Handle(dirent); err != nil {
return offset, err
}
offset++
}
return offset, nil
}
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