github.com/metacubex/gvisor@v0.0.0-20240320004321-933faba989ec/pkg/sentry/vfs/context.go (about)

     1  // Copyright 2019 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 vfs
    16  
    17  import (
    18  	goContext "context"
    19  
    20  	"github.com/metacubex/gvisor/pkg/context"
    21  )
    22  
    23  // contextID is this package's type for context.Context.Value keys.
    24  type contextID int
    25  
    26  const (
    27  	// CtxMountNamespace is a Context.Value key for a MountNamespace.
    28  	CtxMountNamespace contextID = iota
    29  
    30  	// CtxRoot is a Context.Value key for a VFS root.
    31  	CtxRoot
    32  
    33  	// CtxRestoreFilesystemFDMap is a Context.Value key for a map[string]int
    34  	// mapping filesystem unique IDs (cf. gofer.InternalFilesystemOptions.UniqueID)
    35  	// to host FDs.
    36  	CtxRestoreFilesystemFDMap
    37  )
    38  
    39  // MountNamespaceFromContext returns the MountNamespace used by ctx. If ctx is
    40  // not associated with a MountNamespace, MountNamespaceFromContext returns nil.
    41  //
    42  // A reference is taken on the returned MountNamespace.
    43  func MountNamespaceFromContext(ctx goContext.Context) *MountNamespace {
    44  	if v := ctx.Value(CtxMountNamespace); v != nil {
    45  		return v.(*MountNamespace)
    46  	}
    47  	return nil
    48  }
    49  
    50  // RestoreFilesystemFDMapFromContext returns the RestoreFilesystemFDMap used
    51  // by ctx. If ctx is not associated with a RestoreFilesystemFDMap, returns nil.
    52  func RestoreFilesystemFDMapFromContext(ctx goContext.Context) map[RestoreID]int {
    53  	fdmap, ok := ctx.Value(CtxRestoreFilesystemFDMap).(map[RestoreID]int)
    54  	if !ok {
    55  		return nil
    56  	}
    57  	return fdmap
    58  }
    59  
    60  type mountNamespaceContext struct {
    61  	context.Context
    62  	mntns *MountNamespace
    63  }
    64  
    65  // Value implements Context.Value.
    66  func (mc mountNamespaceContext) Value(key any) any {
    67  	switch key {
    68  	case CtxMountNamespace:
    69  		mc.mntns.IncRef()
    70  		return mc.mntns
    71  	default:
    72  		return mc.Context.Value(key)
    73  	}
    74  }
    75  
    76  // WithMountNamespace returns a copy of ctx with the given MountNamespace.
    77  func WithMountNamespace(ctx context.Context, mntns *MountNamespace) context.Context {
    78  	return &mountNamespaceContext{
    79  		Context: ctx,
    80  		mntns:   mntns,
    81  	}
    82  }
    83  
    84  // RootFromContext returns the VFS root used by ctx. It takes a reference on
    85  // the returned VirtualDentry. If ctx does not have a specific VFS root,
    86  // RootFromContext returns a zero-value VirtualDentry.
    87  func RootFromContext(ctx goContext.Context) VirtualDentry {
    88  	if v := ctx.Value(CtxRoot); v != nil {
    89  		return v.(VirtualDentry)
    90  	}
    91  	return VirtualDentry{}
    92  }
    93  
    94  type rootContext struct {
    95  	context.Context
    96  	root VirtualDentry
    97  }
    98  
    99  // WithRoot returns a copy of ctx with the given root.
   100  func WithRoot(ctx context.Context, root VirtualDentry) context.Context {
   101  	return &rootContext{
   102  		Context: ctx,
   103  		root:    root,
   104  	}
   105  }
   106  
   107  // Value implements Context.Value.
   108  func (rc rootContext) Value(key any) any {
   109  	switch key {
   110  	case CtxRoot:
   111  		rc.root.IncRef()
   112  		return rc.root
   113  	default:
   114  		return rc.Context.Value(key)
   115  	}
   116  }