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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 memdev
import (
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/memmap"
"gvisor.dev/gvisor/pkg/sentry/mm"
"gvisor.dev/gvisor/pkg/sentry/pgalloc"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/usermem"
)
const zeroDevMinor = 5
// zeroDevice implements vfs.Device for /dev/zero.
type zeroDevice struct{}
// Open implements vfs.Device.Open.
func (zeroDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
fd := &zeroFD{}
if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
UseDentryMetadata: true,
}); err != nil {
return nil, err
}
return &fd.vfsfd, nil
}
// zeroFD implements vfs.FileDescriptionImpl for /dev/zero.
type zeroFD struct {
vfsfd vfs.FileDescription
vfs.FileDescriptionDefaultImpl
vfs.DentryMetadataFileDescriptionImpl
}
// Release implements vfs.FileDescriptionImpl.Release.
func (fd *zeroFD) Release() {
// noop
}
// PRead implements vfs.FileDescriptionImpl.PRead.
func (fd *zeroFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
return dst.ZeroOut(ctx, dst.NumBytes())
}
// Read implements vfs.FileDescriptionImpl.Read.
func (fd *zeroFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
return dst.ZeroOut(ctx, dst.NumBytes())
}
// PWrite implements vfs.FileDescriptionImpl.PWrite.
func (fd *zeroFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
return src.NumBytes(), nil
}
// Write implements vfs.FileDescriptionImpl.Write.
func (fd *zeroFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
return src.NumBytes(), nil
}
// Seek implements vfs.FileDescriptionImpl.Seek.
func (fd *zeroFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
return 0, nil
}
// ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
func (fd *zeroFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
m, err := mm.NewSharedAnonMappable(opts.Length, pgalloc.MemoryFileProviderFromContext(ctx))
if err != nil {
return err
}
opts.MappingIdentity = m
opts.Mappable = m
return nil
}
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