basic/process-util: modernize setpriority_closest()

Before this commit, the "Cannot raise nice level" branch
is rather confusing, as we're actually lowering the nice.
Also, it's better to log about the final nice value
for both cases, no matter whether we need to set to limit
or not.

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index ede5f8513508a2b58fc061032752223665a7122f..e5dbd6f72d9c0320014b074b11fa67dc6dd46409 100644 (file)
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -1901,17 +1901,15 @@ static int rlimit_to_nice(rlim_t limit) {
 }
 
 int setpriority_closest(int priority) {
-        int current, limit, saved_errno;
         struct rlimit highest;
+        int r, current, limit;
 
         /* Try to set requested nice level */
-        if (setpriority(PRIO_PROCESS, 0, priority) >= 0)
+        r = RET_NERRNO(setpriority(PRIO_PROCESS, 0, priority));
+        if (r >= 0)
                 return 1;
-
-        /* Permission failed */
-        saved_errno = -errno;
-        if (!ERRNO_IS_PRIVILEGE(saved_errno))
-                return saved_errno;
+        if (!ERRNO_IS_NEG_PRIVILEGE(r))
+                return r;
 
         errno = 0;
         current = getpriority(PRIO_PROCESS, 0);
@@ -1925,24 +1923,21 @@ int setpriority_closest(int priority) {
         * then the whole setpriority() system call is blocked to us, hence let's propagate the error
         * right-away */
         if (priority > current)
-                return saved_errno;
+                return r;
 
         if (getrlimit(RLIMIT_NICE, &highest) < 0)
                 return -errno;
 
         limit = rlimit_to_nice(highest.rlim_cur);
 
-        /* We are already less nice than limit allows us */
-        if (current < limit) {
-                log_debug("Cannot raise nice level, permissions and the resource limit do not allow it.");
-                return 0;
-        }
-
-        /* Push to the allowed limit */
-        if (setpriority(PRIO_PROCESS, 0, limit) < 0)
-                return -errno;
+        /* Push to the allowed limit if we're higher than that. Note that we could also be less nice than
+         * limit allows us, but still higher than what's requested. In that case our current value is
+         * the best choice. */
+        if (current > limit)
+                if (setpriority(PRIO_PROCESS, 0, limit) < 0)
+                        return -errno;
 
-        log_debug("Cannot set requested nice level (%i), used next best (%i).", priority, limit);
+        log_debug("Cannot set requested nice level (%i), using next best (%i).", priority, MIN(current, limit));
         return 0;
 }