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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 basic signalfd file implementations.
package signalfd
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
"gvisor.dev/gvisor/pkg/waiter"
)
// SignalFileDescription implements vfs.FileDescriptionImpl for signal fds.
//
// +stateify savable
type SignalFileDescription struct {
vfsfd vfs.FileDescription
vfs.FileDescriptionDefaultImpl
vfs.DentryMetadataFileDescriptionImpl
vfs.NoLockFD
// target is the original signal target task.
//
// 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 mask.
mu sync.Mutex `state:"nosave"`
// mask is the signal mask. Protected by mu.
mask linux.SignalSet
}
var _ vfs.FileDescriptionImpl = (*SignalFileDescription)(nil)
// New creates a new signal fd.
func New(vfsObj *vfs.VirtualFilesystem, target *kernel.Task, mask linux.SignalSet, flags uint32) (*vfs.FileDescription, error) {
vd := vfsObj.NewAnonVirtualDentry("[signalfd]")
defer vd.DecRef(target)
sfd := &SignalFileDescription{
target: target,
mask: mask,
}
if err := sfd.vfsfd.Init(sfd, flags, vd.Mount(), vd.Dentry(), &vfs.FileDescriptionOptions{
UseDentryMetadata: true,
DenyPRead: true,
DenyPWrite: true,
}); err != nil {
return nil, err
}
return &sfd.vfsfd, nil
}
// Mask returns the signal mask.
func (sfd *SignalFileDescription) Mask() linux.SignalSet {
sfd.mu.Lock()
defer sfd.mu.Unlock()
return sfd.mask
}
// SetMask sets the signal mask.
func (sfd *SignalFileDescription) SetMask(mask linux.SignalSet) {
sfd.mu.Lock()
defer sfd.mu.Unlock()
sfd.mask = mask
}
// Read implements vfs.FileDescriptionImpl.Read.
func (sfd *SignalFileDescription) Read(ctx context.Context, dst usermem.IOSequence, _ vfs.ReadOptions) (int64, error) {
// Attempt to dequeue relevant signals.
info, err := sfd.target.Sigtimedwait(sfd.Mask(), 0)
if err != nil {
// There must be no signal available.
return 0, syserror.ErrWouldBlock
}
// Copy out the signal info using the specified format.
infoNative := 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 := infoNative.WriteTo(dst.Writer(ctx))
if err == usermem.ErrEndOfIOSequence {
// Partial copy-out ok.
err = nil
}
return n, err
}
// Readiness implements waiter.Waitable.Readiness.
func (sfd *SignalFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
sfd.mu.Lock()
defer sfd.mu.Unlock()
if mask&waiter.ReadableEvents != 0 && sfd.target.PendingSignals()&sfd.mask != 0 {
return waiter.ReadableEvents // Pending signals.
}
return 0
}
// EventRegister implements waiter.Waitable.EventRegister.
func (sfd *SignalFileDescription) EventRegister(entry *waiter.Entry, _ waiter.EventMask) {
sfd.mu.Lock()
defer sfd.mu.Unlock()
// Register for the signal set; ignore the passed events.
sfd.target.SignalRegister(entry, waiter.EventMask(sfd.mask))
}
// EventUnregister implements waiter.Waitable.EventUnregister.
func (sfd *SignalFileDescription) EventUnregister(entry *waiter.Entry) {
// Unregister the original entry.
sfd.target.SignalUnregister(entry)
}
// Release implements vfs.FileDescriptionImpl.Release.
func (sfd *SignalFileDescription) Release(context.Context) {}
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