mirror of
https://github.com/netbirdio/gvisor.git
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107 lines
3.5 KiB
Go
107 lines
3.5 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package memdev
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import (
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"gvisor.dev/gvisor/pkg/context"
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"gvisor.dev/gvisor/pkg/sentry/fsimpl/tmpfs"
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"gvisor.dev/gvisor/pkg/sentry/kernel"
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"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
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"gvisor.dev/gvisor/pkg/sentry/memmap"
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"gvisor.dev/gvisor/pkg/sentry/vfs"
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"gvisor.dev/gvisor/pkg/usermem"
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)
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const zeroDevMinor = 5
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// zeroDevice implements vfs.Device for /dev/zero.
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//
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// +stateify savable
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type zeroDevice struct{}
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// Open implements vfs.Device.Open.
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func (zeroDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
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fd := &zeroFD{}
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if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
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UseDentryMetadata: true,
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}); err != nil {
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return nil, err
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}
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return &fd.vfsfd, nil
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}
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// zeroFD implements vfs.FileDescriptionImpl for /dev/zero.
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//
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// +stateify savable
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type zeroFD struct {
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vfsfd vfs.FileDescription
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vfs.FileDescriptionDefaultImpl
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vfs.DentryMetadataFileDescriptionImpl
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vfs.NoLockFD
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}
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// Release implements vfs.FileDescriptionImpl.Release.
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func (fd *zeroFD) Release(context.Context) {
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// noop
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}
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// PRead implements vfs.FileDescriptionImpl.PRead.
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func (fd *zeroFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
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return dst.ZeroOut(ctx, dst.NumBytes())
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}
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// Read implements vfs.FileDescriptionImpl.Read.
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func (fd *zeroFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
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return dst.ZeroOut(ctx, dst.NumBytes())
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}
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// PWrite implements vfs.FileDescriptionImpl.PWrite.
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func (fd *zeroFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
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return src.NumBytes(), nil
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}
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// Write implements vfs.FileDescriptionImpl.Write.
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func (fd *zeroFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
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return src.NumBytes(), nil
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}
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// Seek implements vfs.FileDescriptionImpl.Seek.
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func (fd *zeroFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
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return 0, nil
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}
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// ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
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func (fd *zeroFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
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if opts.Private || !opts.MaxPerms.Write {
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// This mapping will never permit writing to the "underlying file" (in
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// Linux terms, it isn't VM_SHARED), so implement it as an anonymous
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// mapping, but back it with fd; this is what Linux does, and is
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// actually application-visible because the resulting VMA will show up
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// in /proc/[pid]/maps with fd.vfsfd.VirtualDentry()'s path rather than
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// "/dev/zero (deleted)".
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opts.Offset = 0
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opts.MappingIdentity = &fd.vfsfd
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opts.SentryOwnedContent = true
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opts.MappingIdentity.IncRef()
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return nil
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}
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tmpfsFD, err := tmpfs.NewZeroFile(ctx, auth.CredentialsFromContext(ctx), kernel.KernelFromContext(ctx).ShmMount(), opts.Length)
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if err != nil {
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return err
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}
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defer tmpfsFD.DecRef(ctx)
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return tmpfsFD.ConfigureMMap(ctx, opts)
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}
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