linux-kernel - [PATCH] kernel/groups.c: use sort library function

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Date:   Mon, 12 Jun 2017 23:02:56 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Michal Hocko <mhocko@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Alexey Dobriyan <adobriyan@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] kernel/groups.c: use sort library function

setgroups is not exactly a hot path, so we might as well use the
library function instead of open-coding the sorting. Saves ~150 bytes.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 kernel/groups.c | 35 +++++++++++------------------------
 1 file changed, 11 insertions(+), 24 deletions(-)

diff --git a/kernel/groups.c b/kernel/groups.c
index d09727692a2a..434f6665f187 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -5,6 +5,7 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/security.h>
+#include <linux/sort.h>
 #include <linux/syscalls.h>
 #include <linux/user_namespace.h>
 #include <linux/vmalloc.h>
@@ -76,32 +77,18 @@ static int groups_from_user(struct group_info *group_info,
 	return 0;
 }
 
-/* a simple Shell sort */
+static int gid_cmp(const void *_a, const void *_b)
+{
+	kgid_t a = *(kgid_t *)_a;
+	kgid_t b = *(kgid_t *)_b;
+
+	return gid_gt(a, b) - gid_lt(a, b);
+}
+
 static void groups_sort(struct group_info *group_info)
 {
-	int base, max, stride;
-	int gidsetsize = group_info->ngroups;
-
-	for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
-		; /* nothing */
-	stride /= 3;
-
-	while (stride) {
-		max = gidsetsize - stride;
-		for (base = 0; base < max; base++) {
-			int left = base;
-			int right = left + stride;
-			kgid_t tmp = group_info->gid[right];
-
-			while (left >= 0 && gid_gt(group_info->gid[left], tmp)) {
-				group_info->gid[right] = group_info->gid[left];
-				right = left;
-				left -= stride;
-			}
-			group_info->gid[right] = tmp;
-		}
-		stride /= 3;
-	}
+	sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
+	     gid_cmp, NULL);
 }
 
 /* a simple bsearch */
-- 
2.1.4