Remove map from fd_map, change to fd_table.

This renames FDMap to FDTable and drops the kernel.FD type, which had an entire
package to itself and didn't serve much use (it was freely cast between types,
and served as more of an annoyance than providing any protection.)

Based on BenchmarkFDLookupAndDecRef-12, we can expect 5-10 ns per lookup
operation, and 10-15 ns per concurrent lookup operation of savings.

This also fixes two tangential usage issues with the FDMap. Namely, non-atomic
use of NewFDFrom and associated calls to Remove (that are both racy and fail to
drop the reference on the underlying file.)

PiperOrigin-RevId: 256285890

1 files changed, 52 insertions, 13 deletions

diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index 2e3a39d3b..e91f82bb3 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -236,15 +236,15 @@ type Task struct {
 	// tc is protected by mu, and is owned by the task goroutine.
 	tc TaskContext
 
-	// fsc is the task's filesystem context.
+	// fsContext is the task's filesystem context.
 	//
-	// fsc is protected by mu, and is owned by the task goroutine.
-	fsc *FSContext
+	// fsContext is protected by mu, and is owned by the task goroutine.
+	fsContext *FSContext
 
-	// fds is the task's file descriptor table.
+	// fdTable is the task's file descriptor table.
 	//
-	// fds is protected by mu, and is owned by the task goroutine.
-	fds *FDMap
+	// fdTable is protected by mu, and is owned by the task goroutine.
+	fdTable *FDTable
 
 	// If vforkParent is not nil, it is the task that created this task with
 	// vfork() or clone(CLONE_VFORK), and should have its vforkStop ended when
@@ -602,7 +602,7 @@ func (t *Task) Value(key interface{}) interface{} {
 	case context.CtxThreadGroupID:
 		return int32(t.ThreadGroup().ID())
 	case fs.CtxRoot:
-		return t.fsc.RootDirectory()
+		return t.fsContext.RootDirectory()
 	case fs.CtxDirentCacheLimiter:
 		return t.k.DirentCacheLimiter
 	case inet.CtxStack:
@@ -668,7 +668,7 @@ func (t *Task) SyscallRestartBlock() SyscallRestartBlock {
 func (t *Task) IsChrooted() bool {
 	realRoot := t.tg.mounts.Root()
 	defer realRoot.DecRef()
-	root := t.fsc.RootDirectory()
+	root := t.fsContext.RootDirectory()
 	if root != nil {
 		defer root.DecRef()
 	}
@@ -689,16 +689,55 @@ func (t *Task) TaskContext() *TaskContext {
 // Precondition: The caller must be running on the task goroutine, or t.mu must
 // be locked.
 func (t *Task) FSContext() *FSContext {
-	return t.fsc
+	return t.fsContext
 }
 
-// FDMap returns t's FDMap. FDMap does not take an additional reference on the
-// returned FDMap.
+// FDTable returns t's FDTable. FDMTable does not take an additional reference
+// on the returned FDMap.
 //
 // Precondition: The caller must be running on the task goroutine, or t.mu must
 // be locked.
-func (t *Task) FDMap() *FDMap {
-	return t.fds
+func (t *Task) FDTable() *FDTable {
+	return t.fdTable
+}
+
+// GetFile is a convenience wrapper t.FDTable().GetFile.
+//
+// Precondition: same as FDTable.
+func (t *Task) GetFile(fd int32) *fs.File {
+	f, _ := t.fdTable.Get(fd)
+	return f
+}
+
+// NewFDs is a convenience wrapper for t.FDTable().NewFDs.
+//
+// This automatically passes the task as the context.
+//
+// Precondition: same as FDTable.
+func (t *Task) NewFDs(fd int32, files []*fs.File, flags FDFlags) ([]int32, error) {
+	return t.fdTable.NewFDs(t, fd, files, flags)
+}
+
+// NewFDFrom is a convenience wrapper for t.FDTable().NewFDs with a single file.
+//
+// This automatically passes the task as the context.
+//
+// Precondition: same as FDTable.
+func (t *Task) NewFDFrom(fd int32, file *fs.File, flags FDFlags) (int32, error) {
+	fds, err := t.fdTable.NewFDs(t, fd, []*fs.File{file}, flags)
+	if err != nil {
+		return 0, err
+	}
+	return fds[0], nil
+}
+
+// NewFDAt is a convenience wrapper for t.FDTable().NewFDAt.
+//
+// This automatically passes the task as the context.
+//
+// Precondition: same as FDTable.
+func (t *Task) NewFDAt(fd int32, file *fs.File, flags FDFlags) error {
+	return t.fdTable.NewFDAt(t, fd, file, flags)
 }
 
 // WithMuLocked executes f with t.mu locked.