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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 (
"sync/atomic"
"unsafe"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/vfs"
)
type descriptorTable struct {
// slice is a *[]unsafe.Pointer, where each element is actually
// *descriptor object, updated atomically.
//
// Changes to the slice itself requiring holding FDTable.mu.
slice unsafe.Pointer `state:".(map[int32]*descriptor)"`
}
// init initializes the table.
func (f *FDTable) init() {
var slice []unsafe.Pointer // Empty slice.
atomic.StorePointer(&f.slice, unsafe.Pointer(&slice))
}
// get gets a file entry.
//
// The boolean indicates whether this was in range.
//
//go:nosplit
func (f *FDTable) get(fd int32) (*fs.File, FDFlags, bool) {
file, _, flags, ok := f.getAll(fd)
return file, flags, ok
}
// getVFS2 gets a file entry.
//
// The boolean indicates whether this was in range.
//
//go:nosplit
func (f *FDTable) getVFS2(fd int32) (*vfs.FileDescription, FDFlags, bool) {
_, file, flags, ok := f.getAll(fd)
return file, flags, ok
}
// getAll gets a file entry.
//
// The boolean indicates whether this was in range.
//
//go:nosplit
func (f *FDTable) getAll(fd int32) (*fs.File, *vfs.FileDescription, FDFlags, bool) {
slice := *(*[]unsafe.Pointer)(atomic.LoadPointer(&f.slice))
if fd >= int32(len(slice)) {
return nil, nil, FDFlags{}, false
}
d := (*descriptor)(atomic.LoadPointer(&slice[fd]))
if d == nil {
return nil, nil, FDFlags{}, true
}
if d.file != nil && d.fileVFS2 != nil {
panic("VFS1 and VFS2 files set")
}
return d.file, d.fileVFS2, d.flags, true
}
// set sets an entry.
//
// This handles accounting changes, as well as acquiring and releasing the
// reference needed by the table iff the file is different.
//
// Precondition: mu must be held.
func (f *FDTable) set(fd int32, file *fs.File, flags FDFlags) {
f.setAll(fd, file, nil, flags)
}
// setVFS2 sets an entry.
//
// This handles accounting changes, as well as acquiring and releasing the
// reference needed by the table iff the file is different.
//
// Precondition: mu must be held.
func (f *FDTable) setVFS2(fd int32, file *vfs.FileDescription, flags FDFlags) {
f.setAll(fd, nil, file, flags)
}
// setAll sets an entry.
//
// This handles accounting changes, as well as acquiring and releasing the
// reference needed by the table iff the file is different.
//
// Precondition: mu must be held.
func (f *FDTable) setAll(fd int32, file *fs.File, fileVFS2 *vfs.FileDescription, flags FDFlags) {
if file != nil && fileVFS2 != nil {
panic("VFS1 and VFS2 files set")
}
slice := *(*[]unsafe.Pointer)(atomic.LoadPointer(&f.slice))
// Grow the table as required.
if last := int32(len(slice)); fd >= last {
end := fd + 1
if end < 2*last {
end = 2 * last
}
slice = append(slice, make([]unsafe.Pointer, end-last)...)
atomic.StorePointer(&f.slice, unsafe.Pointer(&slice))
}
var desc *descriptor
if file != nil || fileVFS2 != nil {
desc = &descriptor{
file: file,
fileVFS2: fileVFS2,
flags: flags,
}
}
// Update the single element.
orig := (*descriptor)(atomic.SwapPointer(&slice[fd], unsafe.Pointer(desc)))
// Acquire a table reference.
if desc != nil {
switch {
case desc.file != nil:
if orig == nil || desc.file != orig.file {
desc.file.IncRef()
}
case desc.fileVFS2 != nil:
if orig == nil || desc.fileVFS2 != orig.fileVFS2 {
desc.fileVFS2.IncRef()
}
}
}
// Drop the table reference.
if orig != nil {
switch {
case orig.file != nil:
if desc == nil || desc.file != orig.file {
f.drop(orig.file)
}
case orig.fileVFS2 != nil:
if desc == nil || desc.fileVFS2 != orig.fileVFS2 {
f.dropVFS2(orig.fileVFS2)
}
}
}
// Adjust used.
switch {
case orig == nil && desc != nil:
atomic.AddInt32(&f.used, 1)
case orig != nil && desc == nil:
atomic.AddInt32(&f.used, -1)
}
}
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