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// Copyright 2018 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 kernel
import (
"fmt"
"sync"
"gvisor.dev/gvisor/pkg/refs"
"gvisor.dev/gvisor/pkg/sentry/fs"
)
// FSContext contains filesystem context.
//
// This includes umask and working directory.
//
// +stateify savable
type FSContext struct {
refs.AtomicRefCount
// mu protects below.
mu sync.Mutex `state:"nosave"`
// root is the filesystem root. Will be nil iff the FSContext has been
// destroyed.
root *fs.Dirent
// cwd is the current working directory. Will be nil iff the FSContext
// has been destroyed.
cwd *fs.Dirent
// umask is the current file mode creation mask. When a thread using this
// context invokes a syscall that creates a file, bits set in umask are
// removed from the permissions that the file is created with.
umask uint
}
// newFSContext returns a new filesystem context.
func newFSContext(root, cwd *fs.Dirent, umask uint) *FSContext {
root.IncRef()
cwd.IncRef()
return &FSContext{
root: root,
cwd: cwd,
umask: umask,
}
}
// destroy is the destructor for an FSContext.
//
// This will call DecRef on both root and cwd Dirents. If either call to
// DecRef returns an error, then it will be propagated. If both calls to
// DecRef return an error, then the one from root.DecRef will be propagated.
//
// Note that there may still be calls to WorkingDirectory() or RootDirectory()
// (that return nil). This is because valid references may still be held via
// proc files or other mechanisms.
func (f *FSContext) destroy() {
// Hold f.mu so that we don't race with RootDirectory() and
// WorkingDirectory().
f.mu.Lock()
defer f.mu.Unlock()
f.root.DecRef()
f.root = nil
f.cwd.DecRef()
f.cwd = nil
}
// DecRef implements RefCounter.DecRef with destructor f.destroy.
func (f *FSContext) DecRef() {
f.DecRefWithDestructor(f.destroy)
}
// Fork forks this FSContext.
//
// This is not a valid call after destroy.
func (f *FSContext) Fork() *FSContext {
f.mu.Lock()
defer f.mu.Unlock()
f.cwd.IncRef()
f.root.IncRef()
return &FSContext{
cwd: f.cwd,
root: f.root,
umask: f.umask,
}
}
// WorkingDirectory returns the current working directory.
//
// This will return nil if called after destroy(), otherwise it will return a
// Dirent with a reference taken.
func (f *FSContext) WorkingDirectory() *fs.Dirent {
f.mu.Lock()
defer f.mu.Unlock()
if f.cwd != nil {
f.cwd.IncRef()
}
return f.cwd
}
// SetWorkingDirectory sets the current working directory.
// This will take an extra reference on the Dirent.
//
// This is not a valid call after destroy.
func (f *FSContext) SetWorkingDirectory(d *fs.Dirent) {
if d == nil {
panic("FSContext.SetWorkingDirectory called with nil dirent")
}
f.mu.Lock()
defer f.mu.Unlock()
if f.cwd == nil {
panic(fmt.Sprintf("FSContext.SetWorkingDirectory(%v)) called after destroy", d))
}
old := f.cwd
f.cwd = d
d.IncRef()
old.DecRef()
}
// RootDirectory returns the current filesystem root.
//
// This will return nil if called after destroy(), otherwise it will return a
// Dirent with a reference taken.
func (f *FSContext) RootDirectory() *fs.Dirent {
f.mu.Lock()
defer f.mu.Unlock()
if f.root != nil {
f.root.IncRef()
}
return f.root
}
// SetRootDirectory sets the root directory.
// This will take an extra reference on the Dirent.
//
// This is not a valid call after free.
func (f *FSContext) SetRootDirectory(d *fs.Dirent) {
if d == nil {
panic("FSContext.SetRootDirectory called with nil dirent")
}
f.mu.Lock()
defer f.mu.Unlock()
if f.root == nil {
panic(fmt.Sprintf("FSContext.SetRootDirectory(%v)) called after destroy", d))
}
old := f.root
f.root = d
d.IncRef()
old.DecRef()
}
// Umask returns the current umask.
func (f *FSContext) Umask() uint {
f.mu.Lock()
defer f.mu.Unlock()
return f.umask
}
// SwapUmask atomically sets the current umask and returns the old umask.
func (f *FSContext) SwapUmask(mask uint) uint {
f.mu.Lock()
defer f.mu.Unlock()
old := f.umask
f.umask = mask
return old
}
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