github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/dirent_state.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package fs
    16  
    17  import (
    18  	"fmt"
    19  	"sync/atomic"
    20  
    21  	"github.com/SagerNet/gvisor/pkg/context"
    22  	"github.com/SagerNet/gvisor/pkg/refs"
    23  )
    24  
    25  // beforeSave is invoked by stateify.
    26  func (d *Dirent) beforeSave() {
    27  	// Refuse to save if the file is on a non-virtual file system and has
    28  	// already been deleted (but still has open fds, which is why the Dirent
    29  	// is still accessible). We know the the restore re-opening of the file
    30  	// will always fail. This condition will last until all the open fds and
    31  	// this Dirent are closed and released.
    32  	//
    33  	// Such "dangling" open files on virtual file systems (e.g., tmpfs) is
    34  	// OK to save as their restore does not require re-opening the files.
    35  	//
    36  	// Note that this is rejection rather than failure---it would be
    37  	// perfectly OK to save---we are simply disallowing it here to prevent
    38  	// generating non-restorable state dumps. As the program continues its
    39  	// execution, it may become allowed to save again.
    40  	if !d.Inode.IsVirtual() && atomic.LoadInt32(&d.deleted) != 0 {
    41  		n, _ := d.FullName(nil /* root */)
    42  		panic(ErrSaveRejection{fmt.Errorf("deleted file %q still has open fds", n)})
    43  	}
    44  }
    45  
    46  // saveChildren is invoked by stateify.
    47  func (d *Dirent) saveChildren() map[string]*Dirent {
    48  	c := make(map[string]*Dirent)
    49  	for name, w := range d.children {
    50  		if rc := w.Get(); rc != nil {
    51  			// Drop the reference count obtain in w.Get()
    52  			rc.DecRef(context.Background())
    53  
    54  			cd := rc.(*Dirent)
    55  			if cd.IsNegative() {
    56  				// Don't bother saving negative Dirents.
    57  				continue
    58  			}
    59  			c[name] = cd
    60  		}
    61  	}
    62  	return c
    63  }
    64  
    65  // loadChildren is invoked by stateify.
    66  func (d *Dirent) loadChildren(children map[string]*Dirent) {
    67  	d.children = make(map[string]*refs.WeakRef)
    68  	for name, c := range children {
    69  		d.children[name] = refs.NewWeakRef(c, nil)
    70  	}
    71  }
    72  
    73  // afterLoad is invoked by stateify.
    74  func (d *Dirent) afterLoad() {
    75  	if d.userVisible {
    76  		allDirents.add(d)
    77  	}
    78  }