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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 signalfd provides an implementation of signal file descriptors.
package signalfd
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/binary"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/fs/anon"
"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
"gvisor.dev/gvisor/pkg/waiter"
)
// SignalOperations represent a file with signalfd semantics.
//
// +stateify savable
type SignalOperations struct {
fsutil.FileNoopRelease `state:"nosave"`
fsutil.FilePipeSeek `state:"nosave"`
fsutil.FileNotDirReaddir `state:"nosave"`
fsutil.FileNoIoctl `state:"nosave"`
fsutil.FileNoFsync `state:"nosave"`
fsutil.FileNoMMap `state:"nosave"`
fsutil.FileNoSplice `state:"nosave"`
fsutil.FileNoWrite `state:"nosave"`
fsutil.FileNoopFlush `state:"nosave"`
fsutil.FileUseInodeUnstableAttr `state:"nosave"`
// target is the original task target.
//
// The semantics here are a bit broken. Linux will always use current
// for all reads, regardless of where the signalfd originated. We can't
// do exactly that because we need to plumb the context through
// EventRegister in order to support proper blocking behavior. This
// will undoubtedly become very complicated quickly.
target *kernel.Task
// mu protects below.
mu sync.Mutex `state:"nosave"`
// mask is the signal mask. Protected by mu.
mask linux.SignalSet
}
// New creates a new signalfd object with the supplied mask.
func New(ctx context.Context, mask linux.SignalSet) (*fs.File, error) {
t := kernel.TaskFromContext(ctx)
if t == nil {
// No task context? Not valid.
return nil, syserror.EINVAL
}
// name matches fs/signalfd.c:signalfd4.
dirent := fs.NewDirent(ctx, anon.NewInode(ctx), "anon_inode:[signalfd]")
return fs.NewFile(ctx, dirent, fs.FileFlags{Read: true, Write: true}, &SignalOperations{
target: t,
mask: mask,
}), nil
}
// Release implements fs.FileOperations.Release.
func (s *SignalOperations) Release() {}
// Mask returns the signal mask.
func (s *SignalOperations) Mask() linux.SignalSet {
s.mu.Lock()
mask := s.mask
s.mu.Unlock()
return mask
}
// SetMask sets the signal mask.
func (s *SignalOperations) SetMask(mask linux.SignalSet) {
s.mu.Lock()
s.mask = mask
s.mu.Unlock()
}
// Read implements fs.FileOperations.Read.
func (s *SignalOperations) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, _ int64) (int64, error) {
// Attempt to dequeue relevant signals.
info, err := s.target.Sigtimedwait(s.Mask(), 0)
if err != nil {
// There must be no signal available.
return 0, syserror.ErrWouldBlock
}
// Copy out the signal info using the specified format.
var buf [128]byte
binary.Marshal(buf[:0], usermem.ByteOrder, &linux.SignalfdSiginfo{
Signo: uint32(info.Signo),
Errno: info.Errno,
Code: info.Code,
PID: uint32(info.Pid()),
UID: uint32(info.Uid()),
Status: info.Status(),
Overrun: uint32(info.Overrun()),
Addr: info.Addr(),
})
n, err := dst.CopyOut(ctx, buf[:])
return int64(n), err
}
// Readiness implements waiter.Waitable.Readiness.
func (s *SignalOperations) Readiness(mask waiter.EventMask) waiter.EventMask {
if mask&waiter.EventIn != 0 && s.target.PendingSignals()&s.Mask() != 0 {
return waiter.EventIn // Pending signals.
}
return 0
}
// EventRegister implements waiter.Waitable.EventRegister.
func (s *SignalOperations) EventRegister(entry *waiter.Entry, _ waiter.EventMask) {
// Register for the signal set; ignore the passed events.
s.target.SignalRegister(entry, waiter.EventMask(s.Mask()))
}
// EventUnregister implements waiter.Waitable.EventUnregister.
func (s *SignalOperations) EventUnregister(entry *waiter.Entry) {
// Unregister the original entry.
s.target.SignalUnregister(entry)
}
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