afd: use IO_STATUS_BLOCK instead of OVERLAPPED to track async poll ops

This reduces per-socket memory usage, as the OVERLAPPED structure
contains some fields that are never used.

src/afd.c

@@ -55,33 +55,18 @@ error:
 
 int afd_poll(HANDLE afd_helper_handle,
              AFD_POLL_INFO* poll_info,
-             OVERLAPPED* overlapped) {
+             IO_STATUS_BLOCK* io_status_block) {
-  IO_STATUS_BLOCK* iosb;
-  HANDLE event;
-  void* apc_context;
   NTSTATUS status;
 
   /* Blocking operation is not supported. */
-  assert(overlapped != NULL);
+  assert(io_status_block != NULL);
 
-  iosb = (IO_STATUS_BLOCK*) &overlapped->Internal;
+  io_status_block->Status = STATUS_PENDING;
-  event = overlapped->hEvent;
-
-  /* Do what other windows APIs would do: if hEvent has it's lowest bit set,
-   * don't post a completion to the completion port. */
-  if ((uintptr_t) event & 1) {
-    event = (HANDLE)((uintptr_t) event & ~(uintptr_t) 1);
-    apc_context = NULL;
-  } else {
-    apc_context = overlapped;
-  }
-
-  iosb->Status = STATUS_PENDING;
   status = NtDeviceIoControlFile(afd_helper_handle,
-                                 event,
                                  NULL,
-                                 apc_context,
+                                 NULL,
-                                 iosb,
+                                 io_status_block,
+                                 io_status_block,
                                  IOCTL_AFD_POLL,
                                  poll_info,
                                  sizeof *poll_info,
@@ -95,3 +80,24 @@ int afd_poll(HANDLE afd_helper_handle,
   else
     return_set_error(-1, RtlNtStatusToDosError(status));
 }
+
+int afd_cancel_poll(HANDLE afd_helper_handle,
+                    IO_STATUS_BLOCK* io_status_block) {
+  NTSTATUS cancel_status;
+  IO_STATUS_BLOCK cancel_iosb;
+
+  /* If the poll operation has already completed or has been cancelled earlier,
+   * there's nothing left for us to do. */
+  if (io_status_block->Status != STATUS_PENDING)
+    return 0;
+
+  cancel_status =
+      NtCancelIoFileEx(afd_helper_handle, io_status_block, &cancel_iosb);
+
+  /* NtCancelIoFileEx() may return STATUS_NOT_FOUND if the operation completed
+   * just before calling NtCancelIoFileEx(). This is not an error. */
+  if (cancel_status == STATUS_SUCCESS || cancel_status == STATUS_NOT_FOUND)
+    return 0;
+  else
+    return_set_error(-1, RtlNtStatusToDosError(cancel_status));
+}

src/afd.h

@@ -34,6 +34,8 @@ WEPOLL_INTERNAL int afd_create_helper_handle(HANDLE iocp_handle,
 
 WEPOLL_INTERNAL int afd_poll(HANDLE afd_helper_handle,
                              AFD_POLL_INFO* poll_info,
-                             OVERLAPPED* overlapped);
+                             IO_STATUS_BLOCK* io_status_block);
+WEPOLL_INTERNAL int afd_cancel_poll(HANDLE afd_helper_handle,
+                                    IO_STATUS_BLOCK* io_status_block);
 
 #endif /* WEPOLL_AFD_H_ */

src/nt.h

@@ -25,6 +25,10 @@ typedef NTSTATUS* PNTSTATUS;
 #define STATUS_CANCELLED ((NTSTATUS) 0xC0000120L)
 #endif
 
+#ifndef STATUS_NOT_FOUND
+#define STATUS_NOT_FOUND ((NTSTATUS) 0xC0000225L)
+#endif
+
 typedef struct _IO_STATUS_BLOCK {
   NTSTATUS Status;
   ULONG_PTR Information;
@@ -65,6 +69,13 @@ typedef struct _OBJECT_ATTRIBUTES {
   (STANDARD_RIGHTS_REQUIRED | KEYEDEVENT_WAIT | KEYEDEVENT_WAKE)
 
 #define NT_NTDLL_IMPORT_LIST(X)           \
+  X(NTSTATUS,                             \
+    NTAPI,                                \
+    NtCancelIoFileEx,                     \
+    (HANDLE FileHandle,                   \
+     PIO_STATUS_BLOCK IoRequestToCancel,  \
+     PIO_STATUS_BLOCK IoStatusBlock))     \
+                                          \
   X(NTSTATUS,                             \
     NTAPI,                                \
     NtCreateFile,                         \

src/port.c

@@ -4,6 +4,7 @@
 #include <string.h>
 
 #include "error.h"
+#include "nt.h"
 #include "poll-group.h"
 #include "port.h"
 #include "queue.h"
@@ -162,10 +163,11 @@ static int port__feed_events(port_state_t* port_state,
   DWORD i;
 
   for (i = 0; i < iocp_event_count; i++) {
-    OVERLAPPED* overlapped = iocp_events[i].lpOverlapped;
+    IO_STATUS_BLOCK* io_status_block =
+        (IO_STATUS_BLOCK*) iocp_events[i].lpOverlapped;
     struct epoll_event* ev = &epoll_events[epoll_event_count];
 
-    epoll_event_count += sock_feed_event(port_state, overlapped, ev);
+    epoll_event_count += sock_feed_event(port_state, io_status_block, ev);
   }
 
   return epoll_event_count;

src/sock.c

@@ -26,7 +26,7 @@ typedef enum sock__poll_status {
 } sock__poll_status_t;
 
 typedef struct sock_state {
-  OVERLAPPED overlapped;
+  IO_STATUS_BLOCK io_status_block;
   AFD_POLL_INFO poll_info;
   queue_node_t queue_node;
   tree_node_t tree_node;
@@ -51,16 +51,11 @@ static inline void sock__free(sock_state_t* sock_state) {
 }
 
 static int sock__cancel_poll(sock_state_t* sock_state) {
-  HANDLE afd_helper_handle =
-      poll_group_get_afd_helper_handle(sock_state->poll_group);
   assert(sock_state->poll_status == SOCK__POLL_PENDING);
 
-  /* CancelIoEx() may fail with ERROR_NOT_FOUND if the overlapped operation has
+  if (afd_cancel_poll(poll_group_get_afd_helper_handle(sock_state->poll_group),
-   * already completed. This is not a problem and we proceed normally. */
+                      &sock_state->io_status_block) < 0)
-  if (!HasOverlappedIoCompleted(&sock_state->overlapped) &&
+    return -1;
-      !CancelIoEx(afd_helper_handle, &sock_state->overlapped) &&
-      GetLastError() != ERROR_NOT_FOUND)
-    return_map_error(-1);
 
   sock_state->poll_status = SOCK__POLL_CANCELLED;
   sock_state->pending_events = 0;
@@ -237,11 +232,9 @@ int sock_update(port_state_t* port_state, sock_state_t* sock_state) {
     sock_state->poll_info.Handles[0].Events =
         sock__epoll_events_to_afd_events(sock_state->user_events);
 
-    memset(&sock_state->overlapped, 0, sizeof sock_state->overlapped);
-
     if (afd_poll(poll_group_get_afd_helper_handle(sock_state->poll_group),
                  &sock_state->poll_info,
-                 &sock_state->overlapped) < 0) {
+                 &sock_state->io_status_block) < 0) {
       switch (GetLastError()) {
         case ERROR_IO_PENDING:
           /* Overlapped poll operation in progress; this is expected. */
@@ -269,10 +262,10 @@ int sock_update(port_state_t* port_state, sock_state_t* sock_state) {
 }
 
 int sock_feed_event(port_state_t* port_state,
-                    OVERLAPPED* overlapped,
+                    IO_STATUS_BLOCK* io_status_block,
                     struct epoll_event* ev) {
   sock_state_t* sock_state =
-      container_of(overlapped, sock_state_t, overlapped);
+      container_of(io_status_block, sock_state_t, io_status_block);
   AFD_POLL_INFO* poll_info = &sock_state->poll_info;
   uint32_t epoll_events = 0;
 
@@ -283,10 +276,10 @@ int sock_feed_event(port_state_t* port_state,
     /* Socket has been deleted earlier and can now be freed. */
     return sock__delete(port_state, sock_state, false);
 
-  } else if ((NTSTATUS) overlapped->Internal == STATUS_CANCELLED) {
+  } else if (io_status_block->Status == STATUS_CANCELLED) {
     /* The poll request was cancelled by CancelIoEx. */
 
-  } else if (!NT_SUCCESS(overlapped->Internal)) {
+  } else if (!NT_SUCCESS(io_status_block->Status)) {
     /* The overlapped request itself failed in an unexpected way. */
     epoll_events = EPOLLERR;
 

src/sock.h

@@ -2,6 +2,7 @@
 #define WEPOLL_SOCK_H_
 
 #include "internal.h"
+#include "nt.h"
 #include "wepoll.h"
 #include "win.h"
 
@@ -24,7 +25,7 @@ WEPOLL_INTERNAL int sock_set_event(port_state_t* port_state,
 WEPOLL_INTERNAL int sock_update(port_state_t* port_state,
                                 sock_state_t* sock_state);
 WEPOLL_INTERNAL int sock_feed_event(port_state_t* port_state,
-                                    OVERLAPPED* overlapped,
+                                    IO_STATUS_BLOCK* io_status_block,
                                     struct epoll_event* ev);
 
 WEPOLL_INTERNAL sock_state_t* sock_state_from_queue_node(