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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/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/fspath"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"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
}
// fdReader provides an io.Reader interface for a vfs.FileDescription.
type fdReader struct {
ctx context.Context
fd *vfs.FileDescription
}
// Read implements io.Reader.Read.
func (f *fdReader) Read(p []byte) (int, error) {
n, err := f.fd.Read(f.ctx, usermem.BytesIOSequence(p), vfs.ReadOptions{})
return int(n), err
}
func cat(k *kernel.Kernel, path string, output *os.File) error {
ctx := k.SupervisorContext()
creds := auth.NewRootCredentials(k.RootUserNamespace())
mns := k.GlobalInit().Leader().MountNamespace()
root := mns.Root(ctx)
defer root.DecRef(ctx)
fd, err := k.VFS().OpenAt(ctx, creds, &vfs.PathOperation{
Root: root,
Start: root,
Path: fspath.Parse(path),
}, &vfs.OpenOptions{
Flags: linux.O_RDONLY,
})
if err != nil {
return fmt.Errorf("failed to open file %s: %v", path, err)
}
defer fd.DecRef(ctx)
_, err = io.Copy(output, &fdReader{ctx: ctx, fd: fd})
return err
}
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