br2: enable taskset, create sched_getaffinity, yet undocumented

kernel_module/user/README.adoc

@@ -12,6 +12,7 @@ These programs can also be compiled and used on host.
 .. link:hello.c[]
 .. link:myinsmod.c[]
 .. link:myrmmod.c[]
+.. link:sched_getaffinity.c[]
 .. link:usermem.c[]
 ... link:pagemap_dump.c[]
 .. inits

kernel_module/user/sched_getaffinity.c

@@ -0,0 +1,44 @@
+/*
+upstream; https://stackoverflow.com/questions/10490756/how-to-use-sched-getaffinity-and-sched-setaffinity-in-linux-from-c/50117787#50117787
+*/
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+void print_affinity() {
+    cpu_set_t mask;
+    long nproc, i;
+
+    if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
+        perror("sched_getaffinity");
+        assert(false);
+    } else {
+        nproc = sysconf(_SC_NPROCESSORS_ONLN);
+        printf("sched_getaffinity = ");
+        for (i = 0; i < nproc; i++) {
+            printf("%d ", CPU_ISSET(i, &mask));
+        }
+        printf("\n");
+    }
+}
+
+int main(void) {
+    cpu_set_t mask;
+
+    print_affinity();
+    printf("sched_getcpu = %d\n", sched_getcpu());
+    CPU_ZERO(&mask);
+    CPU_SET(0, &mask);
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
+        perror("sched_setaffinity");
+        assert(false);
+    }
+    print_affinity();
+    printf("sched_getcpu = %d\n", sched_getcpu());
+    return EXIT_SUCCESS;
+}