sched_get/setaffinity(): try to be more compatible with Linux

in handling the cpuset sizes different from sizeof(cpuset_t).

For both cases, cpuset size shorter than sizeof(cpuset_t) results
in EINVAL on Linux.

For sched_getaffinity(), be more permissive and accept cpuset size
larger than our cpuset_t, by clipping the syscall argument and zeroing
the rest of the output buffer.  For sched_setaffinity(), we should allow
shorter cpusets than current ABI size, again zeroing the rest of the bits.

With this change, python os.sched_get/setaffinity functions work.

Reported by:	se
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/libc/gen/sched_getaffinity.c b/lib/libc/gen/sched_getaffinity.c
index 2ae8c5b763a3..7d345eb82a3b 100644
--- a/lib/libc/gen/sched_getaffinity.c
+++ b/lib/libc/gen/sched_getaffinity.c
@@ -26,11 +26,31 @@
  * SUCH DAMAGE.
  */
 
+#include <errno.h>
 #include <sched.h>
+#include <string.h>
 
 int
 sched_getaffinity(pid_t pid, size_t cpusetsz, cpuset_t *cpuset)
 {
+	/*
+	 * Be more Linux-compatible:
+	 * - return EINVAL in passed size is less than size of cpuset_t
+	 *   in advance, instead of ERANGE from the syscall
+	 * - if passed size is larger than the size of cpuset_t, be
+	 *   permissive by claming it back to sizeof(cpuset_t) and
+	 *   zeroing the rest.
+	 */
+	if (cpusetsz < sizeof(cpuset_t)) {
+		errno = EINVAL;
+		return (-1);
+	}
+	if (cpusetsz > sizeof(cpuset_t)) {
+		memset((char *)cpuset + sizeof(cpuset_t), 0,
+		    cpusetsz - sizeof(cpuset_t));
+		cpusetsz = sizeof(cpuset_t);
+	}
+
 	return (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID,
 	    pid == 0 ? -1 : pid, cpusetsz, cpuset));
 }