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// Copyright 2021 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 control
import (
"fmt"
"io"
"os"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/urpc"
"gvisor.dev/gvisor/pkg/usermem"
)
// CatOpts contains options for the Cat RPC call.
type CatOpts struct {
// Files are the filesystem paths for the files to cat.
Files []string `json:"files"`
// FilePayload contains the destination for output.
urpc.FilePayload
}
// Fs includes fs-related functions.
type Fs struct {
Kernel *kernel.Kernel
}
// Cat is a RPC stub which prints out and returns the content of the files.
func (f *Fs) Cat(o *CatOpts, _ *struct{}) error {
// Create an output stream.
if len(o.FilePayload.Files) != 1 {
return ErrInvalidFiles
}
output := o.FilePayload.Files[0]
for _, file := range o.Files {
if err := cat(f.Kernel, file, output); err != nil {
return fmt.Errorf("cannot read from file %s: %v", file, err)
}
}
return nil
}
// fileReader encapsulates a fs.File and provides an io.Reader interface.
type fileReader struct {
ctx context.Context
file *fs.File
}
// Read implements io.Reader.Read.
func (f *fileReader) Read(p []byte) (int, error) {
n, err := f.file.Readv(f.ctx, usermem.BytesIOSequence(p))
return int(n), err
}
func cat(k *kernel.Kernel, path string, output *os.File) error {
ctx := k.SupervisorContext()
mns := k.GlobalInit().Leader().MountNamespace()
root := mns.Root()
defer root.DecRef(ctx)
remainingTraversals := uint(fs.DefaultTraversalLimit)
d, err := mns.FindInode(ctx, root, nil, path, &remainingTraversals)
if err != nil {
return fmt.Errorf("cannot find file %s: %v", path, err)
}
defer d.DecRef(ctx)
file, err := d.Inode.GetFile(ctx, d, fs.FileFlags{Read: true})
if err != nil {
return fmt.Errorf("cannot get file for path %s: %v", path, err)
}
defer file.DecRef(ctx)
_, err = io.Copy(output, &fileReader{ctx: ctx, file: file})
return err
}
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