chrt: add fallback to be usable on kernels without sched_{get,set}attr

We have fallback for compilation with/without proper glibc and kernel
headers, but it's not enough, because people can switch between
kernels with and without the syscalls. (For example RT kernels for
RHEL/CentOS).

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1353340
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index e934275d7d4d9179a9caa2d6363937ed88d77a67..edae0d9f4898922f318522871668142f1de798f2 100644 (file)
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -58,11 +58,19 @@
 # define SCHED_FLAG_RESET_ON_FORK 0x01
 #endif
 
-
 #if defined (__linux__) && !defined(HAVE_SCHED_SETATTR)
 # include <sys/syscall.h>
 #endif
 
+/* usable kernel-headers, but old glibc-headers */
+#if defined (__linux__) && !defined(SYS_sched_setattr) && defined(__NR_sched_setattr)
+# define SYS_sched_setattr __NR_sched_setattr
+#endif
+
+#if defined (__linux__) && !defined(SYS_sched_getattr) && defined(__NR_sched_getattr)
+# define SYS_sched_getattr __NR_sched_getattr
+#endif
+
 #if defined (__linux__) && !defined(HAVE_SCHED_SETATTR) && defined(SYS_sched_setattr)
 # define HAVE_SCHED_SETATTR
 
@@ -207,12 +215,20 @@ static void show_sched_pid_info(struct chrt_ctl *ctl, pid_t pid)
        if (!pid)
                pid = getpid();
 
+       errno = 0;
+
+       /*
+        * New way
+        */
 #ifdef HAVE_SCHED_SETATTR
        {
                struct sched_attr sa;
 
-               if (sched_getattr(pid, &sa, sizeof(sa), 0) != 0)
+               if (sched_getattr(pid, &sa, sizeof(sa), 0) != 0) {
+                       if (errno == ENOSYS)
+                               goto fallback;
                        err(EXIT_FAILURE, _("failed to get pid %d's policy"), pid);
+               }
 
                policy = sa.sched_policy;
                prio = sa.sched_priority;
@@ -221,8 +237,13 @@ static void show_sched_pid_info(struct chrt_ctl *ctl, pid_t pid)
                runtime = sa.sched_runtime;
                period = sa.sched_period;
        }
-#else /* !HAVE_SCHED_SETATTR */
-       {
+#endif
+
+       /*
+        * Old way
+        */
+fallback:
+       if (errno == ENOSYS) {
                struct sched_param sp;
 
                policy = sched_getscheduler(pid);
@@ -238,7 +259,6 @@ static void show_sched_pid_info(struct chrt_ctl *ctl, pid_t pid)
                        reset_on_fork = 1;
 # endif
        }
-#endif /* !HAVE_SCHED_SETATTR */
 
        if (ctl->altered)
                printf(_("pid %d's new scheduling policy: %s"), pid, get_policy_name(policy));
@@ -315,8 +335,7 @@ static void show_min_max(void)
        }
 }
 
-#ifndef HAVE_SCHED_SETATTR
-static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
+static int set_sched_one_by_setscheduler(struct chrt_ctl *ctl, pid_t pid)
 {
        struct sched_param sp = { .sched_priority = ctl->priority };
        int policy = ctl->policy;
@@ -328,6 +347,13 @@ static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
        return sched_setscheduler(pid, policy, &sp);
 }
 
+
+#ifndef HAVE_SCHED_SETATTR
+static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
+{
+       return set_sched_one_by_setscheduler(ctl, pid);
+}
+
 #else /* !HAVE_SCHED_SETATTR */
 static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
 {
@@ -340,11 +366,20 @@ static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
                .sched_period   = ctl->period,
                .sched_deadline = ctl->deadline
        };
+       int rc;
+
 # ifdef SCHED_RESET_ON_FORK
        if (ctl->reset_on_fork)
                sa.sched_flags |= SCHED_RESET_ON_FORK;
 # endif
-       return sched_setattr(pid, &sa, 0);
+       errno = 0;
+       rc = sched_setattr(pid, &sa, 0);
+
+       if (rc != 0 && errno == ENOSYS && ctl->policy != SCHED_DEADLINE)
+               /* fallback -- build with new kernel/libc, but executed on old kernels */
+               rc = set_sched_one_by_setscheduler(ctl, pid);
+
+       return rc;
 }
 #endif /* HAVE_SCHED_SETATTR */