core/exec-invoke: use sched_setattr instead of sched_setscheduler

The kernel's sched_setattr interface allows for more control over a processes
scheduling attributes as the previously used sched_setscheduler interface.

Using sched_setattr is also the prerequisite for support of utilization
clamping (UCLAMP [1], see #26705) and allows to set sched_runtime. The latter,
sched_runtime, will probably become a relevant scheduling parameter of the
EEVDF scheduler [2, 3], and therefore will not only apply to processes
scheduled via SCHED_DEADLINE, but also for processes scheduled via
SCHED_OTHER/SCHED_BATCH (i.e., most processes).

1: https://docs.kernel.org/next/scheduler/sched-util-clamp.html
2: https://lwn.net/Articles/969062/
3: https://lwn.net/ml/linux-kernel/20240405110010.934104715@infradead.org/

src/basic/missing_sched.h

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <linux/types.h>
 #include <sched.h>
 
 #include "macro.h"
@@ -35,3 +36,20 @@ assert_cc(PF_KTHREAD == 0x00200000);
 #else
 assert_cc(TASK_COMM_LEN == 16);
 #endif
+
+#if !HAVE_STRUCT_SCHED_ATTR
+struct sched_attr {
+        __u32 size;             /* Size of this structure */
+        __u32 sched_policy;     /* Policy (SCHED_*) */
+        __u64 sched_flags;      /* Flags */
+        __s32  sched_nice;      /* Nice value (SCHED_OTHER,
+                                         SCHED_BATCH) */
+        __u32 sched_priority;   /* Static priority (SCHED_FIFO,
+                                       SCHED_RR) */
+        /* Remaining fields are for SCHED_DEADLINE
+           and potentially soon for SCHED_OTHER/SCHED_BATCH */
+        __u64 sched_runtime;
+        __u64 sched_deadline;
+        __u64 sched_period;
+};
+#endif

src/basic/missing_syscall.h

@@ -22,6 +22,7 @@
 
 #include "macro.h"
 #include "missing_keyctl.h"
+#include "missing_sched.h"
 #include "missing_stat.h"
 #include "missing_syscall_def.h"
 
@@ -667,6 +668,22 @@ static inline ssize_t missing_getdents64(int fd, void *buffer, size_t length) {
 
 /* ======================================================================= */
 
+#if !HAVE_SCHED_SETATTR
+
+static inline ssize_t missing_sched_setattr(pid_t pid, struct sched_attr *attr, unsigned int flags) {
+#  if defined __NR_sched_setattr
+        return syscall(__NR_sched_setattr, pid, attr, flags);
+#  else
+        errno = ENOSYS;
+        return -1;
+#  endif
+}
+
+#  define sched_setattr missing_sched_setattr
+#endif
+
+/* ======================================================================= */
+
 /* glibc does not provide clone() on ia64, only clone2(). Not only that, but it also doesn't provide a
  * prototype, only the symbol in the shared library (it provides a prototype for clone(), but not the
  * symbol in the shared library). */