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, 7 insertions, 0 deletions

diff --git a/pkg/refs/refcounter.go b/pkg/refs/refcounter.go
index 3dd6f0dd4..6ecbace9e 100644
--- a/pkg/refs/refcounter.go
+++ b/pkg/refs/refcounter.go
@@ -365,6 +365,8 @@ func (r *AtomicRefCount) ReadRefs() int64 {
 //
 // The sanity check here is limited to real references, since if they have
 // dropped beneath zero then the object should have been destroyed.
+//
+//go:nosplit
 func (r *AtomicRefCount) IncRef() {
 	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
 		panic("Incrementing non-positive ref count")
@@ -379,6 +381,8 @@ func (r *AtomicRefCount) IncRef() {
 // To do this safely without a loop, a speculative reference is first acquired
 // on the object. This allows multiple concurrent TryIncRef calls to
 // distinguish other TryIncRef calls from genuine references held.
+//
+//go:nosplit
 func (r *AtomicRefCount) TryIncRef() bool {
 	const speculativeRef = 1 << 32
 	v := atomic.AddInt64(&r.refCount, speculativeRef)
@@ -420,6 +424,7 @@ func (r *AtomicRefCount) dropWeakRef(w *WeakRef) {
 //	B: DecRef [real decrease]
 //	A: TryIncRef [transform speculative to real]
 //
+//go:nosplit
 func (r *AtomicRefCount) DecRefWithDestructor(destroy func()) {
 	switch v := atomic.AddInt64(&r.refCount, -1); {
 	case v < -1:
@@ -455,6 +460,8 @@ func (r *AtomicRefCount) DecRefWithDestructor(destroy func()) {
 }
 
 // DecRef decrements this object's reference count.
+//
+//go:nosplit
 func (r *AtomicRefCount) DecRef() {
 	r.DecRefWithDestructor(nil)
 }