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, 9 insertions, 18 deletions

diff --git a/runsc/boot/fds.go b/runsc/boot/fds.go
index 59e1b46ec..e5de1f3d7 100644
--- a/runsc/boot/fds.go
+++ b/runsc/boot/fds.go
@@ -21,32 +21,23 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/host"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
-	"gvisor.dev/gvisor/pkg/sentry/kernel/kdefs"
-	"gvisor.dev/gvisor/pkg/sentry/limits"
 )
 
-// createFDMap creates an FD map that contains stdin, stdout, and stderr. If
-// console is true, then ioctl calls will be passed through to the host FD.
+// createFDTable creates an FD table that contains stdin, stdout, and stderr.
+// If console is true, then ioctl calls will be passed through to the host FD.
 // Upon success, createFDMap dups then closes stdioFDs.
-func createFDMap(ctx context.Context, l *limits.LimitSet, console bool, stdioFDs []int) (*kernel.FDMap, error) {
+func createFDTable(ctx context.Context, console bool, stdioFDs []int) (*kernel.FDTable, error) {
 	if len(stdioFDs) != 3 {
 		return nil, fmt.Errorf("stdioFDs should contain exactly 3 FDs (stdin, stdout, and stderr), but %d FDs received", len(stdioFDs))
 	}
 
 	k := kernel.KernelFromContext(ctx)
-	fdm := k.NewFDMap()
-	defer fdm.DecRef()
+	fdTable := k.NewFDTable()
+	defer fdTable.DecRef()
 	mounter := fs.FileOwnerFromContext(ctx)
 
-	// Maps sandbox FD to host FD.
-	fdMap := map[int]int{
-		0: stdioFDs[0],
-		1: stdioFDs[1],
-		2: stdioFDs[2],
-	}
-
 	var ttyFile *fs.File
-	for appFD, hostFD := range fdMap {
+	for appFD, hostFD := range stdioFDs {
 		var appFile *fs.File
 
 		if console && appFD < 3 {
@@ -80,11 +71,11 @@ func createFDMap(ctx context.Context, l *limits.LimitSet, console bool, stdioFDs
 		}
 
 		// Add the file to the FD map.
-		if err := fdm.NewFDAt(kdefs.FD(appFD), appFile, kernel.FDFlags{}, l); err != nil {
+		if err := fdTable.NewFDAt(ctx, int32(appFD), appFile, kernel.FDFlags{}); err != nil {
 			return nil, err
 		}
 	}
 
-	fdm.IncRef()
-	return fdm, nil
+	fdTable.IncRef()
+	return fdTable, nil
 }