Cygwin: Fix return value of sched_getaffinity

Have sched_getaffinity() interface like glibc's, and provide an
undocumented internal interface __sched_getaffinity_sys() like the Linux
kernel's sched_getaffinity() for benefit of taskset(1).

winsup/cygwin/common.din

@@ -98,6 +98,7 @@ __res_querydomain SIGFE
 __res_search SIGFE
 __res_send SIGFE
 __res_state SIGFE
+__sched_getaffinity_sys SIGFE
 __signbitd NOSIGFE
 __signbitf NOSIGFE
 __signgam NOSIGFE

winsup/cygwin/include/cygwin/version.h

@@ -510,7 +510,7 @@ details. */
   337: MOUNT_BINARY -> MOUNT_TEXT
   338: Export secure_getenv.
   339: Export sched_getaffinity, sched_setaffinity, pthread_getaffinity_np,
-       pthread_setaffinity_np.
+       pthread_setaffinity_np, __sched_getaffinity_sys.
 
   Note that we forgot to bump the api for ualarm, strtoll, strtoull,
   sigaltstack, sethostname. */

winsup/cygwin/include/sys/cpuset.h

@@ -9,6 +9,10 @@ details. */
 #ifndef _SYS_CPUSET_H_
 #define _SYS_CPUSET_H_
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef __SIZE_TYPE__ __cpu_mask;
 #define __CPU_SETSIZE 1024  // maximum number of logical processors tracked
 #define __NCPUBITS (8 * sizeof (__cpu_mask))  // max size of processor group
@@ -22,4 +26,10 @@ typedef struct
   __cpu_mask __bits[__CPU_GROUPMAX];
 } cpu_set_t;
 
+int __sched_getaffinity_sys (pid_t, size_t, cpu_set_t *);
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _SYS_CPUSET_H_ */

winsup/cygwin/sched.cc

@@ -555,8 +555,9 @@ done:
 }
 
 int
-sched_getaffinity (pid_t pid, size_t sizeof_set, cpu_set_t *set)
+__sched_getaffinity_sys (pid_t pid, size_t sizeof_set, cpu_set_t *set)
 {
+  /* Emulate Linux raw sched_getaffinity syscall for benefit of taskset(1) */
   HANDLE process = 0;
   int status = 0;
 
@@ -603,14 +604,21 @@ done:
   if (status)
     {
       set_errno (status);
-      status = -1;
+      return -1;
     }
-  else
+
+  /* On successful return, we would ordinarily return 0, but instead we
+     emulate the behavior of the raw sched_getaffinity syscall on Linux. */
+  return min (sizeof_set, sizeof (cpu_set_t));
+}
+
+int
+sched_getaffinity (pid_t pid, size_t sizeof_set, cpu_set_t *set)
 {
-      /* Emulate documented Linux kernel behavior on successful return */
+  /* Emulate the Linux glibc interface of sched_getaffinity() by calling
-      status = wincap.cpu_count ();
+     the raw syscall emulation and mapping positive results to 0. */
-    }
+  int status = __sched_getaffinity_sys (pid, sizeof_set, set);
-  return status;
+  return status > 0 ? 0 : status;
 }
 
 int
@@ -727,9 +735,10 @@ done:
   if (status)
     {
       set_errno (status);
-      status = -1;
+      return -1;
     }
-  return status;
+
+  return 0;
 }
 
 } /* extern C */