swapon: optional -p PRIO support (by Francois Barel <frabar666 AT gmail.com>)

function                                             old     new   delta
swap_on_off_main                                     153     216     +63
packed_usage                                       24190   24214     +24
swap_enable_disable                                  127     131      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 91/0)               Total: 91 bytes

2 files changed, 38 insertions, 6 deletions

diff --git a/util-linux/Config.in b/util-linux/Config.in
index c30091a7a..3b7630e6b 100644
--- a/util-linux/Config.in
+++ b/util-linux/Config.in
@@ -743,6 +743,13 @@ config SWAPONOFF
           space.  If you are not using any swap space, you can leave this
           option disabled.
 
+config FEATURE_SWAPON_PRI
+        bool "Support option -p in swapon"
+        default n
+        depends on SWAPONOFF
+        help
+          Enable support for setting swap device priority in swapon.
+
 config SWITCH_ROOT
         bool "switch_root"
         default n
diff --git a/util-linux/swaponoff.c b/util-linux/swaponoff.c
index beefac030..6eafa3e21 100644
--- a/util-linux/swaponoff.c
+++ b/util-linux/swaponoff.c
@@ -11,6 +11,16 @@
 #include <mntent.h>
 #include <sys/swap.h>
 
+#if ENABLE_FEATURE_SWAPON_PRI
+struct globals {
+        int flags;
+};
+#define G (*(struct globals*)&bb_common_bufsiz1)
+#define g_flags (G.flags)
+#else
+#define g_flags 0
+#endif
+
 static int swap_enable_disable(char *device)
 {
         int status;
@@ -26,7 +36,7 @@ static int swap_enable_disable(char *device)
 #endif
 
         if (applet_name[5] == 'n')
-                status = swapon(device, 0);
+                status = swapon(device, g_flags);
         else
                 status = swapoff(device);
 
@@ -63,15 +73,30 @@ int swap_on_off_main(int argc ATTRIBUTE_UNUSED, char **argv)
 {
         int ret;
 
-        if (!argv[1])
-                bb_show_usage();
-
+#if !ENABLE_FEATURE_SWAPON_PRI
         ret = getopt32(argv, "a");
-        if (ret)
+#else
+        opt_complementary = "p+";
+        ret = getopt32(argv, (applet_name[5] == 'n') ? "ap:" : "a", &g_flags);
+
+        if (ret & 2) { // -p
+                g_flags = SWAP_FLAG_PREFER |
+                        ((g_flags & SWAP_FLAG_PRIO_MASK) << SWAP_FLAG_PRIO_SHIFT);
+                ret &= 1;
+        }
+#endif
+
+        if (ret /* & 1: not needed */) // -a
                 return do_em_all();
 
+        argv += optind;
+        if (!*argv)
+                bb_show_usage();
+
         /* ret = 0; redundant */
-        while (*++argv)
+        do {
                 ret += swap_enable_disable(*argv);
+        } while (*++argv);
+
         return ret;
 }