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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 (
"io"
"math"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/amutex"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/marshal/primitive"
"gvisor.dev/gvisor/pkg/safemem"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/usermem"
"gvisor.dev/gvisor/pkg/waiter"
)
// This file contains Pipe file functionality that is tied to neither VFS nor
// the old fs architecture.
// Release cleans up the pipe's state.
func (p *Pipe) Release(context.Context) {
p.rClose()
p.wClose()
// Wake up readers and writers.
p.Notify(waiter.ReadableEvents | waiter.WritableEvents)
}
// Read reads from the Pipe into dst.
func (p *Pipe) Read(ctx context.Context, dst usermem.IOSequence) (int64, error) {
n, err := dst.CopyOutFrom(ctx, p)
if n > 0 {
p.Notify(waiter.WritableEvents)
}
return n, err
}
// ReadToBlocks implements safemem.Reader.ReadToBlocks for Pipe.Read.
func (p *Pipe) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
n, err := p.read(int64(dsts.NumBytes()), func(srcs safemem.BlockSeq) (uint64, error) {
return safemem.CopySeq(dsts, srcs)
}, true /* removeFromSrc */)
return uint64(n), err
}
func (p *Pipe) read(count int64, f func(srcs safemem.BlockSeq) (uint64, error), removeFromSrc bool) (int64, error) {
p.mu.Lock()
defer p.mu.Unlock()
n, err := p.peekLocked(count, f)
if n > 0 && removeFromSrc {
p.consumeLocked(n)
}
return n, err
}
// WriteTo writes to w from the Pipe.
func (p *Pipe) WriteTo(ctx context.Context, w io.Writer, count int64, dup bool) (int64, error) {
n, err := p.read(count, func(srcs safemem.BlockSeq) (uint64, error) {
return safemem.FromIOWriter{w}.WriteFromBlocks(srcs)
}, !dup /* removeFromSrc */)
if n > 0 && !dup {
p.Notify(waiter.WritableEvents)
}
return n, err
}
// Write writes to the Pipe from src.
func (p *Pipe) Write(ctx context.Context, src usermem.IOSequence) (int64, error) {
n, err := src.CopyInTo(ctx, p)
if n > 0 {
p.Notify(waiter.ReadableEvents)
}
return n, err
}
// WriteFromBlocks implements safemem.Writer.WriteFromBlocks for Pipe.Write.
func (p *Pipe) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
n, err := p.write(int64(srcs.NumBytes()), func(dsts safemem.BlockSeq) (uint64, error) {
return safemem.CopySeq(dsts, srcs)
})
return uint64(n), err
}
func (p *Pipe) write(count int64, f func(safemem.BlockSeq) (uint64, error)) (int64, error) {
p.mu.Lock()
defer p.mu.Unlock()
return p.writeLocked(count, f)
}
// ReadFrom reads from r to the Pipe.
func (p *Pipe) ReadFrom(ctx context.Context, r io.Reader, count int64) (int64, error) {
n, err := p.write(count, func(dsts safemem.BlockSeq) (uint64, error) {
return safemem.FromIOReader{r}.ReadToBlocks(dsts)
})
if n > 0 {
p.Notify(waiter.ReadableEvents)
}
return n, err
}
// Readiness returns the ready events in the underlying pipe.
func (p *Pipe) Readiness(mask waiter.EventMask) waiter.EventMask {
return p.rwReadiness() & mask
}
// Ioctl implements ioctls on the Pipe.
func (p *Pipe) Ioctl(ctx context.Context, io usermem.IO, args arch.SyscallArguments) (uintptr, error) {
// Switch on ioctl request.
switch int(args[1].Int()) {
case linux.FIONREAD:
v := p.queued()
if v > math.MaxInt32 {
v = math.MaxInt32 // Silently truncate.
}
// Copy result to userspace.
iocc := primitive.IOCopyContext{
IO: io,
Ctx: ctx,
Opts: usermem.IOOpts{
AddressSpaceActive: true,
},
}
_, err := primitive.CopyInt32Out(&iocc, args[2].Pointer(), int32(v))
return 0, err
default:
return 0, unix.ENOTTY
}
}
// waitFor blocks until the underlying pipe has at least one reader/writer is
// announced via 'wakeupChan', or until 'sleeper' is cancelled. Any call to this
// function will block for either readers or writers, depending on where
// 'wakeupChan' points.
//
// mu must be held by the caller. waitFor returns with mu held, but it will
// drop mu before blocking for any reader/writers.
func waitFor(mu *sync.Mutex, wakeupChan *chan struct{}, sleeper amutex.Sleeper) bool {
// Ideally this function would simply use a condition variable. However, the
// wait needs to be interruptible via 'sleeper', so we must sychronize via a
// channel. The synchronization below relies on the fact that closing a
// channel unblocks all receives on the channel.
// Does an appropriate wakeup channel already exist? If not, create a new
// one. This is all done under f.mu to avoid races.
if *wakeupChan == nil {
*wakeupChan = make(chan struct{})
}
// Grab a local reference to the wakeup channel since it may disappear as
// soon as we drop f.mu.
wakeup := *wakeupChan
// Drop the lock and prepare to sleep.
mu.Unlock()
cancel := sleeper.SleepStart()
// Wait for either a new reader/write to be signalled via 'wakeup', or
// for the sleep to be cancelled.
select {
case <-wakeup:
sleeper.SleepFinish(true)
case <-cancel:
sleeper.SleepFinish(false)
}
// Take the lock and check if we were woken. If we were woken and
// interrupted, the former takes priority.
mu.Lock()
select {
case <-wakeup:
return true
default:
return false
}
}
// newHandleLocked signals a new pipe reader or writer depending on where
// 'wakeupChan' points. This unblocks any corresponding reader or writer
// waiting for the other end of the channel to be opened, see Fifo.waitFor.
//
// Precondition: the mutex protecting wakeupChan must be held.
func newHandleLocked(wakeupChan *chan struct{}) {
if *wakeupChan != nil {
close(*wakeupChan)
*wakeupChan = nil
}
}
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