[PATCH v2 1/1] Taskset: check first whether affinity is settable

[Carsten Emde <C.Emde@xxxxxxxxx>]

If the PF_NO_SETAFFINITY process flag is set, the user may not
know why the affinity is not settable. Write a respective message
and do not attempt to set the affinity of this process.

Signed-off-by: Carsten Emde <C.Emde@xxxxxxxxx>

---
 schedutils/taskset.c |   53 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

Index: util-linux/schedutils/taskset.c
===================================================================
--- util-linux.orig/schedutils/taskset.c
+++ util-linux/schedutils/taskset.c
@@ -35,6 +35,11 @@
 #include "c.h"
 #include "closestream.h"
 
+#ifndef PF_NO_SETAFFINITY
+#define PF_NO_SETAFFINITY 0x04000000
+#endif
+#define PF_NO_SETAFFINITY_ITEM 9
+
 struct taskset {
 	pid_t		pid;		/* task PID */
 	cpu_set_t	*set;		/* task CPU mask */
@@ -114,6 +119,8 @@ static void __attribute__((__noreturn__)
 
 static void do_taskset(struct taskset *ts, size_t setsize, cpu_set_t *set)
 {
+	char statfilename[32];
+
 	/* read the current mask */
 	if (ts->pid) {
 		if (sched_getaffinity(ts->pid, ts->setsize, ts->set) < 0)
@@ -124,6 +131,52 @@ static void do_taskset(struct taskset *t
 	if (ts->get_only)
 		return;
 
+	/* check whether settable */
+	if (snprintf(statfilename, sizeof(statfilename), "/proc/%d/stat", ts->pid) > 0) {
+		int statfd;
+		char *nosetwarning =
+		    "warning: affinity cannot be set due to PF_NO_SETAFFINITY flag set\n";
+
+		if ((statfd = open(statfilename, O_RDONLY)) > 0) {
+			char stat[1024];
+			int got;
+
+			if ((got = read(statfd, stat, sizeof(stat))) > 0) {
+				char *endptr, *token = stat;
+				int flags, item = PF_NO_SETAFFINITY_ITEM-1;
+
+				token[got] = '\0';
+				while (token != NULL && --item > 0) {
+					token = strchr(token, ' ');
+					if (token != NULL)
+						token++;
+					if (*token != '\0' && *token == '(') {
+						token = strchr(token, ')');
+						if (token != NULL && *token != '\0')
+							token++;
+						if (*token != '\0')
+							token++;
+					}
+				}
+				if (item == 0 && token != NULL && *token != '\0') {
+					char *nextspace = strchr(token, ' ');
+
+					if (nextspace != NULL)
+						*nextspace = '\0';
+					flags = strtol(token, &endptr, 10);
+					if (endptr == token + strlen(token)) {
+						if (flags & PF_NO_SETAFFINITY) {
+							fputs(nosetwarning, stderr);
+							errno = EINVAL;
+							err_affinity(ts->pid, 1);
+						}
+					}
+				}
+			}
+			close(statfd);
+		}
+	}
+
 	/* set new mask */
 	if (sched_setaffinity(ts->pid, setsize, set) < 0)
 		err_affinity(ts->pid, 1);