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, 4 insertions, 5 deletions

diff --git a/pkg/sentry/syscalls/linux/sys_getdents.go b/pkg/sentry/syscalls/linux/sys_getdents.go
index dea872672..7a2beda23 100644
--- a/pkg/sentry/syscalls/linux/sys_getdents.go
+++ b/pkg/sentry/syscalls/linux/sys_getdents.go
@@ -23,14 +23,13 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
-	"gvisor.dev/gvisor/pkg/sentry/kernel/kdefs"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // Getdents implements linux syscall getdents(2) for 64bit systems.
 func Getdents(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	fd := kdefs.FD(args[0].Int())
+	fd := args[0].Int()
 	addr := args[1].Pointer()
 	size := int(args[2].Uint())
 
@@ -46,7 +45,7 @@ func Getdents(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysc
 
 // Getdents64 implements linux syscall getdents64(2).
 func Getdents64(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	fd := kdefs.FD(args[0].Int())
+	fd := args[0].Int()
 	addr := args[1].Pointer()
 	size := int(args[2].Uint())
 
@@ -62,8 +61,8 @@ func Getdents64(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sy
 
 // getdents implements the core of getdents(2)/getdents64(2).
 // f is the syscall implementation dirent serialization function.
-func getdents(t *kernel.Task, fd kdefs.FD, addr usermem.Addr, size int, f func(*dirent, io.Writer) (int, error)) (uintptr, error) {
-	dir := t.FDMap().GetFile(fd)
+func getdents(t *kernel.Task, fd int32, addr usermem.Addr, size int, f func(*dirent, io.Writer) (int, error)) (uintptr, error) {
+	dir := t.GetFile(fd)
 	if dir == nil {
 		return 0, syserror.EBADF
 	}