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// Copyright 2019 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 pipe
import (
"sync"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/sentry/usermem"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/waiter"
)
// This file contains types enabling the pipe package to be used with the vfs
// package.
// VFSPipe represents the actual pipe, analagous to an inode. VFSPipes should
// not be copied.
type VFSPipe struct {
// mu protects the fields below.
mu sync.Mutex `state:"nosave"`
// pipe is the underlying pipe.
pipe Pipe
// Channels for synchronizing the creation of new readers and writers
// of this fifo. See waitFor and newHandleLocked.
//
// These are not saved/restored because all waiters are unblocked on
// save, and either automatically restart (via ERESTARTSYS) or return
// EINTR on resume. On restarts via ERESTARTSYS, the appropriate
// channel will be recreated.
rWakeup chan struct{} `state:"nosave"`
wWakeup chan struct{} `state:"nosave"`
}
// NewVFSPipe returns an initialized VFSPipe.
func NewVFSPipe(sizeBytes, atomicIOBytes int64) *VFSPipe {
var vp VFSPipe
initPipe(&vp.pipe, true /* isNamed */, sizeBytes, atomicIOBytes)
return &vp
}
// NewVFSPipeFD opens a named pipe. Named pipes have special blocking semantics
// during open:
//
// "Normally, opening the FIFO blocks until the other end is opened also. A
// process can open a FIFO in nonblocking mode. In this case, opening for
// read-only will succeed even if no-one has opened on the write side yet,
// opening for write-only will fail with ENXIO (no such device or address)
// unless the other end has already been opened. Under Linux, opening a FIFO
// for read and write will succeed both in blocking and nonblocking mode. POSIX
// leaves this behavior undefined. This can be used to open a FIFO for writing
// while there are no readers available." - fifo(7)
func (vp *VFSPipe) NewVFSPipeFD(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, vfsfd *vfs.FileDescription, flags uint32) (*VFSPipeFD, error) {
vp.mu.Lock()
defer vp.mu.Unlock()
readable := vfs.MayReadFileWithOpenFlags(flags)
writable := vfs.MayWriteFileWithOpenFlags(flags)
if !readable && !writable {
return nil, syserror.EINVAL
}
vfd, err := vp.open(rp, vfsd, vfsfd, flags)
if err != nil {
return nil, err
}
switch {
case readable && writable:
// Pipes opened for read-write always succeed without blocking.
newHandleLocked(&vp.rWakeup)
newHandleLocked(&vp.wWakeup)
case readable:
newHandleLocked(&vp.rWakeup)
// If this pipe is being opened as nonblocking and there's no
// writer, we have to wait for a writer to open the other end.
if flags&linux.O_NONBLOCK == 0 && !vp.pipe.HasWriters() && !waitFor(&vp.mu, &vp.wWakeup, ctx) {
return nil, syserror.EINTR
}
case writable:
newHandleLocked(&vp.wWakeup)
if !vp.pipe.HasReaders() {
// Nonblocking, write-only opens fail with ENXIO when
// the read side isn't open yet.
if flags&linux.O_NONBLOCK != 0 {
return nil, syserror.ENXIO
}
// Wait for a reader to open the other end.
if !waitFor(&vp.mu, &vp.rWakeup, ctx) {
return nil, syserror.EINTR
}
}
default:
panic("invalid pipe flags: must be readable, writable, or both")
}
return vfd, nil
}
// Preconditions: vp.mu must be held.
func (vp *VFSPipe) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, vfsfd *vfs.FileDescription, flags uint32) (*VFSPipeFD, error) {
var fd VFSPipeFD
fd.flags = flags
fd.readable = vfs.MayReadFileWithOpenFlags(flags)
fd.writable = vfs.MayWriteFileWithOpenFlags(flags)
fd.vfsfd = vfsfd
fd.pipe = &vp.pipe
if fd.writable {
// The corresponding Mount.EndWrite() is in VFSPipe.Release().
if err := rp.Mount().CheckBeginWrite(); err != nil {
return nil, err
}
}
switch {
case fd.readable && fd.writable:
vp.pipe.rOpen()
vp.pipe.wOpen()
case fd.readable:
vp.pipe.rOpen()
case fd.writable:
vp.pipe.wOpen()
default:
panic("invalid pipe flags: must be readable, writable, or both")
}
return &fd, nil
}
// VFSPipeFD implements a subset of vfs.FileDescriptionImpl for pipes. It is
// expected that filesystesm will use this in a struct implementing
// vfs.FileDescriptionImpl.
type VFSPipeFD struct {
pipe *Pipe
flags uint32
readable bool
writable bool
vfsfd *vfs.FileDescription
}
// Release implements vfs.FileDescriptionImpl.Release.
func (fd *VFSPipeFD) Release() {
var event waiter.EventMask
if fd.readable {
fd.pipe.rClose()
event |= waiter.EventIn
}
if fd.writable {
fd.pipe.wClose()
event |= waiter.EventOut
}
if event == 0 {
panic("invalid pipe flags: must be readable, writable, or both")
}
if fd.writable {
fd.vfsfd.VirtualDentry().Mount().EndWrite()
}
fd.pipe.Notify(event)
}
// OnClose implements vfs.FileDescriptionImpl.OnClose.
func (fd *VFSPipeFD) OnClose() error {
return nil
}
// PRead implements vfs.FileDescriptionImpl.PRead.
func (fd *VFSPipeFD) PRead(_ context.Context, _ usermem.IOSequence, _ int64, _ vfs.ReadOptions) (int64, error) {
return 0, syserror.ESPIPE
}
// Read implements vfs.FileDescriptionImpl.Read.
func (fd *VFSPipeFD) Read(ctx context.Context, dst usermem.IOSequence, _ vfs.ReadOptions) (int64, error) {
if !fd.readable {
return 0, syserror.EINVAL
}
return fd.pipe.Read(ctx, dst)
}
// PWrite implements vfs.FileDescriptionImpl.PWrite.
func (fd *VFSPipeFD) PWrite(_ context.Context, _ usermem.IOSequence, _ int64, _ vfs.WriteOptions) (int64, error) {
return 0, syserror.ESPIPE
}
// Write implements vfs.FileDescriptionImpl.Write.
func (fd *VFSPipeFD) Write(ctx context.Context, src usermem.IOSequence, _ vfs.WriteOptions) (int64, error) {
if !fd.writable {
return 0, syserror.EINVAL
}
return fd.pipe.Write(ctx, src)
}
// Ioctl implements vfs.FileDescriptionImpl.Ioctl.
func (fd *VFSPipeFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
return fd.pipe.Ioctl(ctx, uio, args)
}
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