[Toybox] [PATCH] nice.c: don't bother with getpriority().

[Avery Pennarun]

The nice() syscall returns either 0 for success (very old Linux kernels) or
the new niceness (which might be -1).  To check whether it was successful,
the nice(2) manpage says you should zero out errno, then if nice() returns
-1, check that errno is nonzero, and if it is, that's your error.

We could call getpriority(), but the way it was being done is incorrect.
getpriority() includes the *absolute* priority of the process, while nice()
adjusts the priority incrementally.  To use getpriority() correctly, we'd
have to get the priority before and after, and cap it at the
kernel-dependent range, and make sure the *delta* is the one we requested
with nice(2).  This is unnecessary since the return value of nice() is
perfectly sufficient.
---
 toys/nice.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/toys/nice.c b/toys/nice.c
index 0be7488..401e309 100644
--- a/toys/nice.c
+++ b/toys/nice.c
@@ -34,8 +34,8 @@ void nice_main(void)
 {
 	if (!toys.optflags) TT.priority = 10;
 
-	nice(TT.priority);
-	if (getpriority(PRIO_PROCESS, getpid()) != TT.priority)
+	errno = 0;
+	if (nice(TT.priority) == -1 && errno != 0)
 		perror_exit("Can't set priority");
 
 	xexec(toys.optargs);
-- 
1.7.9.dirty